libakgl/TODO.md

TODO

Internal consistency

Findings from a sweep of src/ and include/. These are consistency and convention problems, not new functional defects — where one has a functional consequence it is called out. Ordered roughly by blast radius. Items that overlap the existing Defects list are cross-referenced rather than repeated.

1. Public naming conventions

Items 1 through 6 are resolved in 0.5.0, which is an ABI break and carries the soname to libakgl.so.0.5. What changed, and what a consumer has to rename:

Was	Is
_ASSETS_H_, _CONTROLLER_H_, _DRAW_H_, _ERROR_H_, _JSON_HELPERS_H_, _PHYSICS_H_, _REGISTRY_H_, _RENDERER_H_, _TEXT_H_, _TILEMAP_H_, _UTIL_H_, _STRING_H_	_AKGL_<FILE>_H_
akgl_Actor_cmhf_* (8 functions)	akgl_actor_cmhf_*
akgl_game_updateFPS	akgl_game_update_fps
akgl_render_init2d, akgl_render_bind2d	akgl_render_2d_init, akgl_render_2d_bind
akgl_sprite_sheet_coords_for_frame	akgl_spritesheet_coords_for_frame
point, RectanglePoints	akgl_Point, akgl_RectanglePoints
window, bgm, game, gamemap, renderer, physics, camera	the same, akgl_-prefixed
_akgl_renderer, _akgl_physics, _akgl_camera, _akgl_gamemap	akgl_default_renderer, akgl_default_physics, akgl_default_camera, akgl_default_gamemap
HEAP_ACTOR, HEAP_SPRITE, HEAP_SPRITESHEET, HEAP_CHARACTER, HEAP_STRING	akgl_heap_actors, akgl_heap_sprites, akgl_heap_spritesheets, akgl_heap_characters, akgl_heap_strings
GAME_ControlMaps	akgl_controlmaps
AKGL_SPRITE_MAX_CHARACTER_NAME_LENGTH	AKGL_CHARACTER_MAX_NAME_LENGTH
AKGL_TIME_ONESEC_MS	AKGL_TIME_ONEMS_NS

include/akgl/staticstring.h also stopped guarding with _STRING_H_ — a name several libc implementations use for their own <string.h> — and its #include "string.h" is now #include <string.h>.

akgl_render_bind2d was not on the original list. It is the same defect as akgl_render_init2d, 2d trailing where the six functions it installs carry it in the middle, and renaming one without the other would have been worse than renaming neither.

The renames were done by renaming each declaration and letting the compiler find every use, rather than by pattern substitution. That distinction matters for renderer, physics and camera, which are also parameter and struct-member names: a sed would have rewritten map->physics and every akgl_RenderBackend *renderer parameter, and nothing would have complained.

Item 6 had a live bug behind the name, now fixed. akgl_game_state_lock counted its retry loop against a constant named "one second in milliseconds" that held 1000000, so it retried 10,000 times at 100 ms and blocked for roughly sixteen minutes before reporting failure. The budget is now AKGL_GAME_STATE_LOCK_BUDGET_MS (1000), with the cadence named separately as AKGL_GAME_STATE_LOCK_RETRY_MS. tests/game.c carries test_game_state_lock_budget, which holds the mutex from a second thread and asserts the call gives up between half a second and five. The old code fails it by timing the suite out; a build that gave up without waiting at all fails the lower bound. Nothing exercised the contended path before — the existing lock test only ever took an uncontended mutex, which never reaches the retry loop.

Item 4 was not cosmetic, and the proof was sitting in the test suite. renderer was exported from the shared library, and tests/character.c defined an SDL_Renderer *renderer of its own. Both had external linkage and the same spelling, so the executable's definition preempted the library's: akgl_sprite_load_json read a SDL_Renderer * through an akgl_RenderBackend *, every texture load in that suite failed with Parameter 'renderer' is invalid, and the suite still reported success — see "Test suites that could not fail" below. It now binds a real backend with akgl_render_2d_bind, the way tests/sprite.c and tests/text.c do. A consuming game with a variable called renderer would have hit the same thing with no test to notice.

2. Header/implementation surface drift

7. Nineteen non-static functions are defined in src/ but declared in no header. They have external linkage and public-looking names, so they are part of the ABI whether intended or not, and no consumer can call them:

   akgl_game_load_objectnamemap, akgl_game_load_versioncmp, akgl_game_save_actors, akgl_game_save_actorname_iterator, akgl_game_save_charactername_iterator, akgl_game_save_spritename_iterator, akgl_game_save_spritesheetname_iterator (src/game.c); akgl_get_json_properties_double, akgl_get_json_properties_float, akgl_get_json_properties_number, akgl_tilemap_load_layer_image, akgl_tilemap_load_layer_object_actor, akgl_tilemap_load_physics (src/tilemap.c); akgl_path_relative_from, akgl_path_relative_root (src/util.c); gamepad_handle_added, gamepad_handle_button_down, gamepad_handle_button_up, gamepad_handle_removed (src/controller.c).

   Each should be either declared in its header or made static. Note that tilemap.h already has a "part of the internal API, exposed here for unit testing" block — the tilemap entries belong there.

8. akgl_game_init_screen is declared but never defined (include/akgl/game.h:100). Same failure mode as Defects → Known and still open #10, which covers the four akgl_controller_handle_* declarations; fold this one into that item.

9. Static helpers use three different naming styles. actor_visible (src/actor.c:185) is bare; akgl_character_load_json_inner and akgl_character_load_json_state_int_from_strings (src/character.c:101,132) and akgl_sprite_load_json_spritesheet (src/sprite.c:51) carry the full public prefix; gamepad_handle_* (src/controller.c:121+) uses a third subsystem word that appears nowhere else. Adopt one rule — the clearest is that static helpers drop the akgl_ prefix, since it exists to avoid external collisions.

10. Parameter names disagree between declaration and definition. Doxygen documents the header spelling, so the generated docs describe names the implementation does not use:

    Header	Implementation
    character.h:41 basechar	character.c:21 obj
    character.h:69 props	character.c:75 registry
    heap.h:121 ptr	heap.c:143 basechar — fixed in 0.5.0
    registry.h:97 value	registry.c:163 src
    json_helpers.h:134 e	json_helpers.c:149 err
    tilemap.h:134,143 dest	tilemap.c:646,767 map

    The tilemap.h pair is the most misleading: the parameter is the map being read and drawn, but it is named dest and documented as "Output destination populated by the function".

11. Object-pool size macros are defined twice, and the override hook is dead. heap.h:15-29 wraps AKGL_MAX_HEAP_ACTOR, _SPRITE, _SPRITESHEET, _CHARACTER, and _STRING in #ifndef guards so a consumer can override them, but actor.h:65, sprite.h:19-20, and character.h:14 define the same four unconditionally and are included from heap.h:9-11. Whichever header lands first wins and the #ifndef never fires, so the override mechanism cannot work. Define each pool size once — heap.h is the natural home.

12. Headers rely on their includers for types. iterator.h used uint32_t without <stdint.h>; json_helpers.h used json_t without <jansson.h>; util.h used SDL_FRect and bool without any SDL include. Each compiled only because of .c-file include ordering.

    Resolved, and enforced rather than merely fixed. AKGL_PUBLIC_HEADERS in CMakeLists.txt is now the single list behind both install() and a generated translation unit per header — each including exactly that header and nothing before it — linked into the headers suite. A header that ships is a header that is checked, and adding one to that list is all a new header needs.

    Writing the check found a case this item had missed: registry.h uses SDL_PropertiesID in eight declarations and included no SDL header at all. That is the argument for generating the check off the install list instead of hand-listing the headers thought to be at risk.

13. Include spelling is split between quoted and angled forms for the same directory. Resolved. Every in-project include in a public header uses #include <akgl/sibling.h>. tests/*.c still use #include "testutil.h", correctly: that one is a test-local header rather than an installed one.

14. Empty parameter lists. akgl_heap_init(), akgl_heap_init_actor(), akgl_registry_init*(), akgl_game_init(), akgl_game_init_screen(), and akgl_game_updateFPS() declare () rather than (void), while akgl_controller_list_keyboards(void), akgl_controller_open_gamepads(void), akgl_game_lowfps(void), and akgl_game_state_lock(void) use (void). Before C23 the two are not equivalent — () suppresses argument checking. akgl_heap_init_actor is even declared () in heap.h:57 and defined (void) in heap.c:48.

15. AKERR_NOIGNORE is applied inconsistently at definition sites. Headers use it uniformly (except akgl_sprite_sheet_coords_for_frame, sprite.h:86, which omits it). Definitions are split even within one file: registry.c:55,120,163,172 repeat it, registry.c:27,44,63,71,79,96,104,112 do not. Since the attribute is already on the declaration, drop it from all definitions.

3. Error-handling pattern

16. *_RETURN macros are used inside ATTEMPT blocks, which skips CLEANUP. The established pattern is FAIL_*_BREAK / CATCH inside ATTEMPT and *_RETURN outside it. Violations:

    • src/tilemap.c:52 — SUCCEED_RETURN on the success path of akgl_get_json_tilemap_property returns directly from inside ATTEMPT, bypassing the CLEANUP at line 54 that releases tmpstr and typestr. Every successful property lookup leaks two heap strings, and the string pool is only 256 entries.
    • src/tilemap.c:620 — FAIL_RETURN inside ATTEMPT.
    • src/controller.c:286-289,306 — FAIL_ZERO_RETURN / FAIL_NONZERO_RETURN inside ATTEMPT; src/controller.c:383 — SUCCEED_RETURN inside ATTEMPT, which also leaves akgl_controller_default with no return statement on the path that falls out of FINISH.
    • src/game.c:457,462 — FAIL_NONZERO_RETURN inside ATTEMPT, skipping the fclose in CLEANUP at line 482.

17. NULL-check discipline varies by function. In src/json_helpers.c only akgl_get_json_string_value (line 71) and akgl_get_json_array_index_string (line 128) validate key/dest; the other eight accessors validate only the container and then dereference dest unconditionally. In src/physics.c the arcade backends check actor but akgl_physics_null_gravity, _null_collide, and _null_move (lines 15-34) check only self. In src/renderer.c:65,74, akgl_render_2d_frame_start and _frame_end dereference self->sdl_renderer with no check on self, while akgl_render_2d_draw_texture (line 82) checks self first.

18. Error-context variable naming is split between errctx and e, sometimes within one file. src/util.c uses e in the path helpers (lines 32-116) and errctx in the geometry helpers (lines 118-259); src/heap.c uses errctx everywhere except akgl_heap_init_actor (line 50). src/actor.c, character.c, json_helpers.c, registry.c, sprite.c, and tilemap.c favor errctx; game.c, physics.c, renderer.c, and controller.c favor e. Pick one.

4. Types and macros

19. float/double are used raw where types.h defines aliases. types.h exports float32_t and float64_t, and the actor and character structs use float32_t throughout — but akgl_get_json_number_value takes float * (json_helpers.h:55), akgl_get_json_double_value takes double * (line 66), akgl_PhysicsBackend's six drag/gravity fields are double (physics.h:22-27), and akgl_Tilemap's perspective fields are float (tilemap.h:105-108). Either use the aliases consistently or delete them.

20. AKGL_COLLIDE_RECTANGLES (include/akgl/util.h:27) has unbalanced parentheses — three opens, two closes — so any use is a syntax error. It has no callers and duplicates akgl_collide_rectangles. Delete it.

21. Bitmask macros are unparenthesized. AKGL_BITMASK_HAS(x, y) expands to (x & y) == y with no outer parens, so !AKGL_BITMASK_HAS(a, b) parses as !(a & b) == b. No in-tree caller negates it today (AKGL_BITMASK_HASNOT exists for that), so this is latent rather than live. AKGL_BITMASK_CLEAR(x) (game.h:86) also carries a trailing semicolon inside the macro body, so normal use produces an empty statement. Parenthesize all five and drop the semicolon.

22. The state and iterator bit macros mix forms. AKGL_ITERATOR_OP_UPDATE (iterator.h:15) is written 1 while its 31 siblings are 1 << n, and none of the 1 << n values in iterator.h or actor.h:15-49 are parenthesized. The hand-maintained trailing bit-pattern comments in actor.h:34-49 are also wrong for the high word — they restart at 0000 0000 0000 0001 for bit 16 rather than showing the full 32-bit value.

23. akgl_Frame (game.h:27-31) is defined and never used anywhere in src/, include/, tests/, or util/.

5. AKGL_ACTOR_STATE_STRING_NAMES disagrees with actor.h

24. The array bound differs between declaration and definition. include/akgl/actor.h:57 declares [AKGL_ACTOR_MAX_STATES+1] (33); src/actor_state_string_names.c:6 defines [32]. Any consumer that trusts the declared bound and reads index 32 reads past the object.

25. Two entries name the wrong bit. actor.h assigns bit 11 to AKGL_ACTOR_STATE_MOVING_IN and bit 12 to AKGL_ACTOR_STATE_MOVING_OUT, but actor_state_string_names.c:18-19 puts "AKGL_ACTOR_STATE_UNDEFINED_11" and "AKGL_ACTOR_STATE_UNDEFINED_12" at those indices — names for macros that do not exist. Since akgl_registry_init_actor_state_strings (src/registry.c:79-94) builds AKGL_REGISTRY_ACTOR_STATE_STRINGS from this array and akgl_character_load_json_state_int_from_strings (src/character.c:101) resolves character-JSON state names through it, a character JSON can never bind a sprite to MOVING_IN or MOVING_OUT.

26. The generation comment is stale. actor.h:53-55 says the file "is built by a utility script and not kept in git, see the Makefile for lib_src/actor_state_string_names.c". There is no Makefile (the project is CMake), no lib_src/, no such script under scripts/ or util/, and the file is tracked in git at src/actor_state_string_names.c. Either restore the generator — which would fix items 24 and 25 by construction — or delete the comment and maintain the file by hand.

6. Doxygen drift

27. Three struct doc comments in tilemap.h are rotated by one. akgl_TilemapObject (line 31) is documented as "Stores tileset metadata, texture, and frame offsets" (that is akgl_Tileset); akgl_TilemapLayer (line 46) as "Represents an object embedded in a tilemap layer" (that is akgl_TilemapObject); akgl_Tileset (line 61) as "Stores tile, image, or object data for one map layer" (that is akgl_TilemapLayer).

28. point is documented as "Represents a two-dimensional point" (util.h:12) but has x, y, and z.

29. Doc comments live on the definition for public functions. The convention is header-side documentation, but akgl_path_relative_root (util.c:23), akgl_path_relative_from (util.c:97), the four gamepad_handle_* (controller.c:114+), the akgl_game_save_* iterators and akgl_game_load_* helpers (game.c:173+), and the tilemap helpers (tilemap.c:90+) are documented only in the .c. This is the same set as item 7 — resolving that resolves this.

7. Formatting

30. A minority of files use a 2-column offset instead of the canonical 4-column one. The mix of tabs and spaces across most of src/ is not disorder: it is exactly what Emacs cc-mode emits for the stroustrup style with indent-tabs-mode t and tab-width 8 — depth 1 is four spaces, depth 2 is one tab, depth 3 is a tab plus four spaces, and so on. Twelve of the seventeen .c files follow that ladder cleanly.

    The genuine outliers indent at 2 columns: src/json_helpers.c (82 lines, except akgl_get_json_with_default at line 149 which is 4), src/util.c (37 lines, from akgl_rectangle_points at line 118 onward), src/assets.c (9), src/staticstring.c (7), src/actor.c (8, in akgl_actor_add_child at line 272), plus include/akgl/util.h (7) and include/akgl/staticstring.h (2).

    Resolved. AGENTS.md now specifies the canonical style and the exact cc-mode settings; .dir-locals.el applies them in Emacs; and scripts/reindent.sh applies them in batch. The whole tree (32 files across src/, include/, tests/, and util/) has been reindented and is a fixed point of scripts/reindent.sh --check. Verified whitespace-only: apart from three trailing blank lines removed at EOF in src/heap.c, src/registry.c, and tests/tilemap.c, git diff -w over the reindent is empty, and the test results are unchanged (13/14, character still the intentional failure). scripts/hooks/pre-commit keeps it that way — enable with git config core.hooksPath scripts/hooks.

31. Leftover debug code ships in the library. src/controller.c:91-97 logs four lines whenever event->type == 768 && event->key.which == 11 && event->key.key == 13 — hardcoded decimal values for a specific keyboard ID on a specific developer's machine, inside the per-event inner loop.

32. Large commented-out blocks. src/sprite.c:115-120,157,185-198,210; src/character.c:192-199,215; src/assets.c:18-27,50; src/tilemap.c:583,596-598,640. All are the same abandoned SDL_GetBasePath() path-prefixing approach, superseded by akgl_path_relative. Delete them.

33. Unused locals. screenwidth/screenheight (game.c:53-54), curTime (game.c:499), curTime and j (renderer.c:114,116 — j is also shadowed by the inner loop at line 128), target (character.c:59), result (util.c:37,73), opflags (heap.c:146, declared and cleared but never read).

34. akgl_game_update's default flags OR the same bit twice. src/game.c:496 reads (AKGL_ITERATOR_OP_LAYERMASK | AKGL_ITERATOR_OP_LAYERMASK). Given the loop that follows walks layers and calls updatefunc, the intent was almost certainly AKGL_ITERATOR_OP_UPDATE | AKGL_ITERATOR_OP_LAYERMASK.

35. akgl_draw_background is the only public function outside the error protocol. include/akgl/draw.h:14 returns void and reports nothing; every other public entry point returns akerr_ErrorContext *. It also calls SDL_SetRenderDrawColor and SDL_RenderFillRect without checking renderer or renderer->sdl_renderer.

36. akgl_registry_init_actor is the only registry initializer that destroys an existing registry before recreating it (src/registry.c:47-49). The other seven leak the old SDL_PropertiesID on a second call. Either all of them should do it or none should.

37. Redundant casts obscure the code. (json_t *)json where json is already json_t *, (akgl_Tilemap *)dest, (akgl_Actor *)actorobj, (char *)&obj->name on an array that already decays — roughly 180 pointer casts across src/, a large majority of them no-ops, densest in src/tilemap.c:150-624 and src/character.c:144-172. They suppress exactly the conversion warnings that would catch a real mismatch.

38. struct-qualified parameters in two definitions. akgl_physics_null_move (src/physics.c:29) and akgl_physics_arcade_move (src/physics.c:80) are defined with struct akgl_PhysicsBackend *self while the header and the other eight physics functions use the typedef.

39. text.c:19 validates the wrong argument. FAIL_ZERO_RETURN(errctx, name, AKERR_NULLPOINTER, "Null filepath") checks name a second time; filepath is never checked and is passed straight to TTF_OpenFont. Copy-paste of line 18.

    Resolved alongside the text measurement work; tests/text.c asserts a NULL filepath reports AKERR_NULLPOINTER.

40. akgl_path_relative and akgl_path_relative_from disagree on the output parameter. akgl_path_relative and akgl_path_relative_root take akgl_String *dst; akgl_path_relative_from takes akgl_String **dst (src/util.c:105). The ** form matches the rest of the library (akgl_get_json_string_value, akgl_get_property, akgl_heap_next_string), which allocate when *dest is NULL. Related: Defects → Known and still open #4, which covers the fact that akgl_path_relative_from never writes *dst at all.

41. dst vs dest for output parameters. akgl_string_copy and the akgl_path_relative* family use dst; everything else uses dest.

Test suites that could not fail

Found while renaming the exported globals, and the reason item 4 above is filed as a real defect rather than a style complaint. Both are fixed.

Every suite reported success on any status whose low byte is zero. libakerror's default unhandled-error handler ends in exit(errctx->status). exit keeps only the low byte of what it is given, and libakgl's status band starts at AKERR_FIRST_CONSUMER_STATUS, which is 256. AKGL_ERR_SDL is therefore exactly 256, exit(256) is a wait status of 0, and CTest recorded a pass. The most common failure status in a library built on SDL was the one status that could not fail a test.

tests/character.c was green while running one of its four tests. It aborted in test_character_sprite_mgmt with Failed loading asset .../spritesheet.png : Parameter 'renderer' is invalid — the symbol collision described in item 4 — and exited 0 because that status was AKGL_ERR_SDL. Two independent defects had to line up, and they did, for long enough that TODO.md recorded the suite as passing and wondered which change had fixed it. Nothing had; it had stopped running.

Fixed in tests/testutil.h: TEST_TRAP_UNHANDLED_ERRORS() installs a handler that collapses any status a byte cannot carry onto 1, and every suite's main() calls it immediately after akgl_error_init(). tests/error.c calls it after its first test instead, because that suite has no akgl_error_init() in main() and libakerror's lazy akerr_init() would overwrite the handler.

Once installed, no other suite changed colour, so this was not masking anything beyond character — but it could have been at any time, and nothing would have said so.

Worth knowing: the fix belongs here rather than in libakerror only because exit(status) is a reasonable thing for a library to do when statuses fit in a byte. libakerror's own band does. Consumers' bands start at 256 by construction, so any consumer's test suites have this problem. That is worth raising upstream.

Coverage status

Generated with:

cmake -S . -B build-coverage -DAKGL_COVERAGE=ON -DCMAKE_BUILD_TYPE=Debug
cmake --build build-coverage --parallel
ctest --test-dir build-coverage --output-on-failure

Reports land in build-coverage/coverage/ (index.html, coverage.xml).

Line coverage 79.6%, function coverage 87.2% (2189/2749 lines, 164/188 functions), up from 77.2% / 83.1% and from a 39.6% / 44.3% baseline. All 21 suites pass. (An earlier revision of this file recorded character as an intentionally failing suite; it passes now, and nothing in tests/character.c or src/character.c has changed since — the fix came from elsewhere in the tree and this note was never updated.)

Note the trap described in "Known and still open" item 13 while regenerating these numbers: a coverage tree rebuilt after a source edit fails coverage_reset with GCOV returncode was 5. find build-coverage -name '*.gcda' -delete clears it.

File	Lines	Functions
src/actor.c	205/258 (80%)	16/18
src/assets.c	0/21 (0%)	0/1
src/audio.c	229/248 (92%)	22/23
src/character.c	104/118 (88%)	6/7
src/controller.c	300/329 (91%)	16/16
src/draw.c	253/267 (95%)	11/12
src/error.c	9/9 (100%)	1/1
src/game.c	128/235 (54%)	12/17
src/heap.c	111/111 (100%)	12/12
src/json_helpers.c	111/111 (100%)	11/11
src/physics.c	140/140 (100%)	10/10
src/registry.c	76/102 (74%)	11/12
src/renderer.c	42/75 (56%)	7/8
src/sprite.c	93/101 (92%)	5/5
src/staticstring.c	16/17 (94%)	2/2
src/text.c	48/48 (100%)	4/4
src/tilemap.c	201/426 (47%)	10/20
src/util.c	121/131 (92%)	7/8
src/version.c	2/2 (100%)	1/1

Branch coverage reads 21.2% and should not be used as a target. The akerror control-flow macros (ATTEMPT/CATCH/PROCESS/FINISH, FAIL_*_RETURN) expand into large branch trees per call site, most of them unreachable in normal operation — src/game.c reports over 1700 branches across 230 lines. Track line and function coverage; treat branch coverage as a relative signal within a file.

Mutation testing

scripts/mutation_test.py was run over the three new files as a smoke check (--max-mutants 8 to 10 each, so these are samples rather than exhaustive scores):

File	Score	Surviving mutants
src/draw.c	90%	Deleting the FAIL_ZERO_BREAK on SDL_CreateTextureFromSurface in akgl_draw_flood_fill
src/audio.c	75%	Deleting SUCCEED_RETURN from the static check_voice; deleting spec.freq before opening a device
src/text.c	50%	Three in akgl_text_rendertextat, which had no test yet, plus one SUCCEED_RETURN deletion

The first pass over src/audio.c scored 50% and named two real gaps, both of which are now tested: nothing asserted that an unconfigured voice is audible (the whole reason the table defaults to a square wave at full level rather than a zeroed struct), and no envelope test used a non-zero attack and decay together, so the decay measuring from the wrong origin survived. src/draw.c scored 70% first and named one: the circle was only checked at its four axis points, which a mis-signed octant reflection survives, so it now checks that every plotted pixel has a mirror in the other three quadrants.

Re-run as a smoke check after the akbasic API work, again at 10 sampled mutants each:

File	Score	Surviving mutants
src/controller.c	40%	Three SDL_Log deletions; keybuffer_head's initialiser; count > 0 in keybuffer_attach_text; the mod a text-only entry is given
src/audio.c	60%	The break on the last switch case; errctx->handled in the device callback; ensure_voices() in the mixer; the mixer's voice loop bound

Only one of those was a real gap and it is now asserted: nothing checked that a text-only ring entry reports no modifiers. Of the rest, three are equivalent mutants rather than misses — a ring buffer whose head starts at 1 behaves identically, count > 0 cannot be false where it is checked, and deleting the break on a switch's last case changes nothing — and the mixer's v <= bound reads one voice past a zeroed table, which is undefined rather than observable. SDL_Log deletions are unobservable by construction.

What is left is honestly untestable from here. Deleting a SUCCEED_RETURN leaves a non-void function falling off its end, which is undefined rather than observably wrong, and the surviving SDL branches are allocation failures the suite has no way to provoke. The three src/text.c survivors in akgl_text_rendertextat are gone: it is tested now, against a software renderer, and deleting any of its three backend checks fails the suite. That was not free — the first draft of the test used a made-up SDL_Renderer pointer, which SDL refuses on its own, so the deleted-check mutant survived it. A live renderer was what made the check observable.

Suites

Every suite is registered through the AKGL_TEST_SUITES list in CMakeLists.txt, which drives target creation, CTest registration, the WORKING_DIRECTORY/TIMEOUT properties, the link line, and the FIXTURES_REQUIRED akgl_coverage list together. Adding tests/<name>.c and the name to that list is all a new suite needs; it can no longer be accidentally left out of the coverage fixture.

Shared assertion helpers are in tests/testutil.h: TEST_ASSERT, TEST_ASSERT_FEQ, TEST_EXPECT_STATUS, TEST_EXPECT_OK, TEST_EXPECT_ANY_ERROR, and TEST_ASSERT_FLAG. All except the last expand to a break on failure, so they belong directly inside an ATTEMPT block, not inside a loop nested in one.

Done:

• tests/physics.c — both backends, the factory, and the full simulation loop including thrust clamping, drag, layer masking, parent/child positioning, and logic-interrupt handling. 100%.
• tests/heap.c — pool exhaustion for all five pools, refcount clamping, recursive child release, registry cleanup on release. 100%.
• tests/json_helpers.c — every typed accessor, both string accessors' allocate-vs-reuse paths, array bounds, and akgl_get_json_with_default. 100%.
• tests/controller.c — control map push and capacity, the default binding set, keyboard and gamepad dispatch including cross-device rejection, the dpad handlers, and device add/remove against the dummy drivers. 90%.
• tests/game.c — version gating, the save/load roundtrip, foreign-save rejection, truncated-table detection, the state lock, and FPS accounting. 54%.
• tests/actor.c — extended with the eight control-map handlers, automatic facing, movement logic, the animation frame state machine, akgl_actor_update, and character/sprite binding lookups. 80%.
• tests/audio.c — every waveform, the ADSR envelope stage by stage, gate expiry and release, the frequency sweep frame by frame, voice summing and clamping, the master level, and device open/shutdown under the dummy driver. 92%.
• tests/draw.c — every primitive against a 64x64 software renderer with the pixels read back, including flood-fill containment, save/paste roundtrip, and that drawing restores the renderer's draw color. 95%.
• tests/text.c — font loading into the registry, both measurement entry points against a monospaced fixture font, and drawing through a bound backend over a software renderer, including every way the backend can be unusable. 100%.
• tests/renderer.c — the 2D vtable binding, frame start and end, both draw_texture paths, the refusals a bound-but-unrendered backend gives, and the draw_mesh stub. 56%; akgl_render_init2d and akgl_render_2d_draw_world are what is left, and both want the harness.
• tests/headers.c — that akgl/controller.h compiles as the first include in a translation unit. The assertion is the compile; main() only has to return zero.

Remaining work

Needs the offscreen renderer harness

akgl_render_init2d and akgl_render_2d_draw_world in src/renderer.c (33 lines), akgl_draw_background in src/draw.c (13), src/assets.c (21), akgl_actor_render/actor_visible in src/actor.c (53), and the drawing half of src/tilemap.c all need a live renderer global, a window, or the world globals.

akgl_text_rendertextat was on this list and is not any more: tests/text.c builds a software renderer and binds a backend to it with akgl_render_bind2d in nine lines, which is enough for anything that only needs a renderer rather than the whole world. tests/renderer.c and tests/draw.c do the same. The harness is still wanted, but for what is left it is a convenience rather than the blocker it was.

Build tests/harness.c / tests/harness.h with akgl_test_init_headless() and akgl_test_shutdown_headless(): set the dummy video and audio drivers, SDL_Init(), akgl_heap_init(), akgl_registry_init(), create a software SDL_CreateWindowAndRenderer, and point the global renderer at it. Seven existing tests hand-roll this today (tests/sprite.c:194, tests/character.c:200, tests/tilemap.c:421, tests/charviewer.c:42, plus tests/draw.c, tests/renderer.c and tests/text.c); collapse them onto the shared harness in the same change.

Then:

• tests/renderer.c extensions — akgl_render_init2d populating the camera from the property registry, and draw_world layer ordering. tests/renderer.c exists and covers everything that does not need a world or the registry: the vtable binding, frame start/end against a NULL sdl_renderer, both draw_texture paths including angle != 0 with a NULL center, and the draw_mesh stub. Note defflags at src/renderer.c:113 is uninitialized until the if body runs.
• tests/assets.c — BGM loading into AKGL_REGISTRY_MUSIC under the dummy audio driver.
• tests/draw.c extensions — akgl_draw_background at zero, negative and oversized dimensions. tests/draw.c exists and covers every other primitive against a software renderer; akgl_draw_background is the one function in the file that still reads the global renderer rather than taking a backend.
• tests/tilemap.c extensions — akgl_tilemap_draw, _draw_tileset, and akgl_tilemap_load_layer_image.

Does not need a renderer

• src/tilemap.c — akgl_tilemap_scale_actor is pure math over three branches (src/tilemap.c:824-830); akgl_get_json_properties_number, _float, and _double need only a JSON snippet; akgl_tilemap_load_physics needs a fixture with the physics property block present, absent, and malformed. Together roughly 100 of the 225 uncovered lines.
• src/game.c — akgl_game_init, akgl_game_update, akgl_game_lowfps, and akgl_game_updateFPS's frame loop need a window; revisit after the harness lands.
• src/registry.c — akgl_registry_load_properties needs a fixture with a properties object, plus the missing-file, missing-key, and wrong-value-type cases. Assert the loop at src/registry.c:148-158 does not leak the string heap.

Defects

Fixed while building the suites

Each was found by a test written to assert correct behavior.

1. akgl_physics_simulate dereferenced self before its NULL check. src/physics.c:132 read self->gravity_time at declaration time, three lines above FAIL_ZERO_RETURN(e, self, ...). A NULL backend segfaulted.
2. akgl_game_save never flushed or closed its stream. CLEANUP and PROCESS were transposed, which put the fclose inside the PROCESS switch, where it only ran if an error context existed and reported success. An ordinary save produced an empty file.
3. akgl_game_save_actors wrote name-table terminators from a single char. aksl_fwrite((void *)&nullval, 1, AKGL_ACTOR_MAX_NAME_LENGTH, fp) emitted 127 bytes of adjacent stack memory into the save file and produced a sentinel the loader could not recognize.
4. akgl_game_load_objectnamemap swallowed read failures. CATCH used directly inside while (1) breaks the loop, not the function, so a truncated or corrupt name table loaded as a successful game.
5. akgl_Actor_cmhf_up_on and _down_on dereferenced basechar unguarded, unlike their left and right counterparts.
6. akgl_actor_logic_movement checked actor twice instead of checking actor->basechar before dereferencing it.
7. The gamepad handlers checked appstate three times each, so a NULL event or a missing player actor was never caught and player->state was dereferenced regardless.

Known and still open

1. akgl_render_and_compare compares a texture against itself. src/util.c:228 and src/util.c:245 both draw t1; t2 is never rendered, so the function always passes and the image assertions in tests/sprite.c assert nothing.

2. akgl_tilemap_release double-frees tileset textures. src/tilemap.c:849 destroys dest->tilesets[i].texture inside the layers loop; it should be dest->layers[i].texture. It also never NULLs the pointers, so a second release is a use-after-free.

3. akgl_registry_init never initializes the properties registry. akgl_registry_init_properties() is not called from akgl_registry_init() (src/registry.c:27), so AKGL_REGISTRY_PROPERTIES stays 0 unless the caller initializes it separately. akgl_set_property is then a silent no-op and akgl_get_property always returns the caller's default, which means akgl_physics_init_arcade and akgl_render_init2d silently ignore configuration. akgl_game_init does call it; a caller that does not use akgl_game_init does not get it.

4. akgl_path_relative_from is a stub that leaks. src/util.c:105 claims a heap string, never writes *dst, and never releases it. 256 calls exhaust the string pool.

5. akgl_compare_sdl_surfaces memcmps without checking geometry. src/util.c:208 compares s1->pitch * s1->h bytes of s2 without verifying the surfaces share dimensions, pitch, or format.

6. akgl_string_initialize overflows by four bytes when init is NULL. src/staticstring.c:17 does memset(&obj->data, 0x00, sizeof(akgl_String)), but data starts four bytes into the struct (after refcount), so the memset runs four bytes past the end.

7. Savegame name lengths disagree between writer and reader. akgl_game_save_actors writes spritesheet names at AKGL_SPRITE_SHEET_MAX_FILENAME_LENGTH (512) and character names at AKGL_SPRITE_MAX_CHARACTER_NAME_LENGTH (128), but akgl_game_load reads every table at AKGL_ACTOR_MAX_NAME_LENGTH (128). A save with any registered spritesheet cannot be read back. The current roundtrip test passes only because empty registries write nothing but zeroed sentinels.

8. Heap acquire functions are asymmetric. akgl_heap_next_string increments refcount; next_actor, next_sprite, next_spritesheet, and next_character do not. tests/heap.c pins the current behavior and says so; decide whether to make them symmetric or document the split.

9. tests/util.c defines test_akgl_collide_point_rectangle_logic but main() never calls it.

10. controller.h declares functions that do not exist. It declares akgl_controller_handle_button_down, _button_up, _added, and _removed, but src/controller.c defines them as gamepad_handle_*. Anything compiled against the header alone fails to link.

11. akgl_controller_pushmap and akgl_controller_default accept negative map ids. Both check controlmapid >= AKGL_MAX_CONTROL_MAPS but not controlmapid < 0, so a negative id indexes before GAME_ControlMaps.

12. A failed controller-DB fetch silently destroys the tracked fallback. include/akgl/SDL_GameControllerDB.h is committed deliberately so the library still builds if upstream disappears. But mkcontrollermappings.sh has no set -e and never checks curl's exit status: on a failed fetch it writes mappings.txt empty, then overwrites the good tracked header with AKGL_SDL_GAMECONTROLLER_DB_LEN 0 and an empty initializer — and exits 0. Verified by pointing the script at an unresolvable host.

    Two compounding problems:

    • add_custom_command at CMakeLists.txt:89-93 declares OUTPUT include/akgl/SDL_GameControllerDB.h as a relative path, which CMake resolves against the binary directory, while the script writes to the source directory. The declared output never appears, so the command is permanently out of date and re-runs on every build — making every build depend on network access and leaving the file dirty in the working tree each time.
    • const char *SDL_GAMECONTROLLER_DB[] = {\n}; is an empty initializer, which is a constraint violation in ISO C and compiles only as a GCC extension.

    Fix: have the script fetch to a temporary file, check curl's status and a plausible minimum line count, and leave the existing header untouched on failure (exiting non-zero). Separately, make regeneration explicit — a dedicated controllerdb target, or an OUTPUT that matches where the script actually writes — so an ordinary build neither needs the network nor dirties the tree.

13. A stale build tree in the source directory breaks the coverage run. CMakeLists.txt:208 and CMakeLists.txt:223 pass --root "${CMAKE_CURRENT_SOURCE_DIR}" to gcovr, and gcovr searches for .gcda/.gcno files under the root. The --object-directory argument on the line below each does not narrow that search: per gcovr --help it only identifies "the path between gcda files and the directory where the compiler was originally run". So every instrumented build tree left inside the source directory is folded into the report alongside the one actually being measured.

    With a build-coverage/ from an earlier session still present, a freshly configured -DAKGL_COVERAGE=ON tree fails in coverage_reset, before any test runs:

    AssertionError: Got function akgl_game_lowfps on multiple lines: 45, 46.
    

    45 and 46 are that function's line numbers before and after an unrelated #include was added to src/game.c: gcovr found 18 stale .gcno files describing the old layout, merged them with the current ones, and could not reconcile the two. Moving build-coverage/ aside makes the same tree pass 18/18. Verified with gcovr 7.0.

    The build*/ entry in .gitignore hides these trees from git status, which makes the state easier to get into and no easier to notice.

    A second, smaller version of the same thing: rebuilding an existing coverage tree after editing a test leaves .gcda files describing the old object layout, and coverage_reset -- whose whole job is to delete them -- fails with GCOV returncode was 5 before it gets the chance. find build-coverage -name '*.gcda' -delete clears it. Observed with gcovr 7.0.

    Fix: pass the build tree to gcovr as an explicit search path instead of letting it default to --root, so only the tree under measurement is considered. Touches the two add_test blocks at CMakeLists.txt:204-211 and CMakeLists.txt:220-229; nothing outside the AKGL_COVERAGE branch.

14. 22 public symbols shipped without a version or soname bump. 42b60f7 added akgl_draw_point, _line, _rect, _filled_rect, _circle, _flood_fill, _copy_region and _paste_region; akgl_audio_init, _shutdown, _tone, _stop, _waveform, _envelope, _volume, _voice_active and _mix; akgl_controller_poll_key and _flush_keys; and akgl_text_measure and _measure_wrapped. project(akgl VERSION 0.1.0) and the libakgl.so.0.1 soname were both left alone.

    That contradicts this repository's own stated rule, which akbasic's CLAUDE.md quotes back: "for both 0.x libraries the soname carries MAJOR.MINOR deliberately: 0.1 and 0.2 are different ABIs." Adding exported symbols under an unchanged soname has two consequences, and the first is the one that bites:

    • A binary compiled against the new headers links happily against a libakgl.so.0.1 built from the old tree, because the soname says they are the same ABI. It fails at symbol resolution rather than at configure time.
    • AKGL_VERSION_AT_LEAST(0, 1, 0) is true for both trees, so a consumer cannot feature-test for the new API at all. akbasic pins the requirement by submodule commit instead, and says so in its README, which is not a thing a released library should make anybody do.

    Fix: bump project() to 0.2.0, which carries the soname to libakgl.so.0.2 through the existing logic at CMakeLists.txt:138. akstdlibConfigVersion.cmake's SameMinorVersion equivalent then refuses the mismatch at configure time as well.

    Resolved by 1066ac7, which did exactly that while this was being written — the two crossed, rather than one following the other. Kept rather than deleted because the reason is still the useful part: akbasic could not feature-test for the new API and had to pin libakgl by submodule commit in its README until this landed, which is the concrete cost of an additive release under an unchanged soname. Worth remembering the next time a handful of symbols looks too small to bump for.

Found while rewriting the Doxygen comments

Each of these came out of reading an implementation against the contract its header claimed. They are recorded inline as @note or @warning on the function concerned, so a reader of the generated documentation finds them without coming here first. Ordered by blast radius.

15. akgl_path_relative leaks one error-context slot per call on its fallback path. src/util.c:120 returns akgl_path_relative_root(...) from inside the HANDLE(e, ENOENT) block. FINISH is what carries RELEASE_ERROR, so returning before it never gives the context back. libakerror hands these out of a fixed AKERR_ARRAY_ERROR[128], and this is not a rare path — it is the ordinary one, taken every time an asset names a neighbour relative to its own file rather than to the working directory. Every tileset image, layer image and spritesheet in a map costs a slot, permanently. Once the array is exhausted every subsequent failure anywhere in the process has nowhere to report from.

    Fix: assign the result to a local, break, and return after FINISH; or hoist the fallback out of the handler entirely and let the HANDLE block only record that a retry is wanted. Touches src/util.c:117-121 only.

16. akgl_sprite_load_json does not bound the frames array. src/sprite.c:165 sets obj->frames from json_array_size() and src/sprite.c:167 then writes that many entries into frameids[AKGL_SPRITE_MAX_FRAMES], which is 16. A sprite definition with 17 or more frames writes past the array into the rest of akgl_Sprite, and past the struct into the neighbouring pool slot. It is also written through a uint32_t * cast of a uint8_t *, so each element write touches four bytes; that happens to work on a little-endian machine because the following iterations overwrite the spill and the last write lands in the struct's alignment padding, but it is not portable and it is what makes the overflow reach four bytes past frames rather than one.

    Fix: refuse a frames array longer than AKGL_SPRITE_MAX_FRAMES with AKERR_OUTOFBOUNDS, and read into an int local before narrowing to uint8_t. Touches src/sprite.c:164-169.

17. Two more unbounded array loads in the tilemap loader. src/tilemap.c:387-389 walks a Tiled object layer straight into curlayer->objects[j] with no check against AKGL_TILEMAP_MAX_OBJECTS_PER_LAYER (128), and src/tilemap.c:278-280 fills dest->tilesets[i] with no check against AKGL_TILEMAP_MAX_TILESETS (16). Both are the same shape as item 16 and both are reachable from an ordinary map file: 128 objects is not a large object layer. Note that akgl_tilemap_load_layers does bound its loop and raises AKERR_OUTOFBOUNDS, so the pattern to copy is already in the same file.

    Fix: add the bound check at the top of each loop body, matching akgl_tilemap_load_layers. Touches src/tilemap.c:387 and src/tilemap.c:278.

18. akgl_get_json_with_default defaults on a status the array accessors never raise. src/json_helpers.c:164-165 handles AKERR_KEY and AKERR_INDEX, but akgl_get_json_array_index_object, _integer and _string all report a short array as AKERR_OUTOFBOUNDS. So the "this element is optional" form silently does not work for an array — the error propagates instead of being replaced by the default. Only the object accessors, which do raise AKERR_KEY, are actually served by this function today. Nothing in tree passes an array accessor's error here, which is why it has not been noticed.

    Fix: add a third HANDLE_GROUP(err, AKERR_OUTOFBOUNDS). Note that the existing two rely on HANDLE_GROUP not emitting a break, so the KEY case falls through into the INDEX body — a third arm has to go above the one holding the memcpy, not below it. Touches src/json_helpers.c:164-167.

19. The background music never loops. src/assets.c:20 initialises bgmprops to 0, src/assets.c:44 sets MIX_PROP_PLAY_LOOPS_NUMBER on it, and src/assets.c:46 plays the track with it. 0 is SDL's "no property set" sentinel, not a set this function owns, so the write is rejected — unchecked — and the play call is given no options. The music plays once and stops. akgl_load_start_bgm reports success either way.

    Fix: SDL_CreateProperties() into bgmprops, check it, and destroy it in CLEANUP. Touches src/assets.c:20-47.

20. akgl_character_sprite_add leaks a sprite reference when a state is remapped. src/character.c:51 writes the new sprite over any existing entry for that state without releasing the one it displaces, whose refcount was incremented when it was added. The displaced sprite's pool slot is never reclaimed. The write itself is also unchecked, so a failure to record the mapping is reported as success.

    Fix: read the existing entry first and akgl_heap_release_sprite it, and check SDL_SetPointerProperty's return. Touches src/character.c:43-55.

21. akgl_heap_release_character abandons the whole state-to-sprite map. src/heap.c:150 zeroed the character without walking state_sprites, so every sprite reference the character took in akgl_character_sprite_add was lost and the SDL_PropertiesID holding the map was never destroyed. Loading and releasing characters in a loop — level to level — exhausted the sprite pool and leaked an SDL property set each time.

    Fixed in 0.5.0. At a refcount of zero it enumerates state_sprites with akgl_character_state_sprites_iterate and AKGL_ITERATOR_OP_RELEASE, then SDL_DestroyProperties, then zeroes the slot. The iterator existed for exactly this walk and simply was never called from here.

    The test was already written. tests/character.c has asserted this contract all along — "character did not reduce reference count of its child sprites when released" — and had never once run, for the two reasons under "Test suites that could not fail". It runs now, and it fails against the old code.

    Still open and separate: item 20, akgl_character_sprite_add leaking the displaced sprite when a state is remapped. Releasing at character teardown does not cover a binding replaced while the character is alive.

22. akgl_path_relative_root uses FAIL_RETURN inside its ATTEMPT block. src/util.c:75 returns past CLEANUP on the over-long-path branch, so the two scratch strings claimed at src/util.c:67-68 are never released. This is the exact hazard AGENTS.md documents under the error-handling protocol, and the same class as the heap-string leak already fixed in akgl_get_json_tilemap_property. Smaller blast radius than item 15 because the branch is rare, but it is a mechanical fix.

    Fix: FAIL_BREAK. Touches src/util.c:75.

23. Three smaller leaks on failure paths. All the same shape: a resource acquired before an ATTEMPT/CLEANUP pair, or released only on the success path.

    • src/renderer.c:26-32 — akgl_render_init2d releases the two pooled strings holding the screen dimensions only after both aksl_atoi calls succeed, so a non-numeric game.screenwidth leaks two string slots.
    • src/controller.c:80 — akgl_controller_open_gamepads calls SDL_free(gamepads) only after the loop completes, so a gamepad that fails to open leaks the enumeration array.
    • src/text.c:57-64 — akgl_text_rendertextat destroys the surface and texture only on the success path, so a failed texture upload or a failed draw leaks both. On a HUD line redrawn every frame that is a leak per frame.

24. akgl_get_property reads past the end of the property value. src/registry.c:182 copies a fixed AKGL_MAX_STRING_LENGTH bytes out of whatever SDL_GetStringProperty returned, rather than that string's length. The destination is a full-sized pool string so nothing is corrupted, but the source is an ordinary NUL-terminated string owned by SDL and the read runs up to PATH_MAX bytes past its end. Benign in practice and immediately fatal under ASAN, which is the reason to fix it rather than leave it.

    Fix: aksl_strlcpy or an explicit length. Touches src/registry.c:181-186.

25. akgl_character_load_json_state_int_from_strings checks the same argument twice. src/character.c:123 guards states and src/character.c:124 guards states again under the message "NULL destination integer" — the guard for dest was never written. A NULL dest is dereferenced at src/character.c:132. Only reachable from inside the character loader, which always passes a real pointer, so it is a latent hole rather than a live bug.

    Fix: change the second guard's subject to dest. Touches src/character.c:124.

26. akgl_actor_render computes a sprite's drawn height from its width. src/actor.c:276 sets dest.h = curSprite->width * obj->scale where it should read curSprite->height. Every actor is therefore drawn square, and a non-square sprite is stretched or squashed. Invisible in the current assets because they are square; it will not stay that way.

    Fix: one word. Touches src/actor.c:276. Worth a test that renders a deliberately non-square sprite and asserts on the destination rectangle.

Found while closing the akbasic API gaps

27. akgl_text_rendertextat refuses the empty string, and akgl_text_measure accepts it. SDL_ttf returns NULL with "Text has zero width" from both TTF_RenderText_Blended and TTF_RenderText_Blended_Wrapped for "", so src/text.c:56's FAIL_ZERO_RETURN on the surface reports AKERR_NULLPOINTER for what a caller means as "draw nothing". Verified directly against SDL_ttf 3.x with the fixture font.

    akgl_text_measure("") is documented as legal and returns 0 wide by one line high, which is what a cursor sitting on an empty line needs, so the two halves of the same header disagree about the same string. The functional consequence is a caller that draws a line of text which may be empty — a line editor, a PRINT of an empty string, a HUD field that has not been filled in yet — has to test for it before every call or handle a failure that means nothing went wrong.

    Fix: return success without rasterizing when text[0] == '\0', matching the measure side, and say so in the header. Touches akgl_text_rendertextat only. tests/text.c has the case written and deliberately not asserted; it would become a TEST_EXPECT_OK. Until then the header carries the wart as a @note pointing here.

Performance

The first measured baseline is in PERFORMANCE.md, produced by tests/perf.c and tests/perf_render.c (ctest --test-dir build -L perf). Both suites hold every measurement to a budget set at roughly ten times the recorded baseline, so an algorithmic regression fails the suite rather than being discovered by a player. Read PERFORMANCE.md before arguing with anything below — every claim here has a number behind it, and several of the things I expected to be slow are not.

Defects the perf suites found

Ordered by blast radius. Numbering continues the Defects list above.

28. akgl_path_relative leaked an error context on every root-fallback resolution. src/util.c:118 took its ENOENT branch by returning from inside the HANDLE block, which skips the RELEASE_ERROR that FINISH ends with. One entry of AKERR_ARRAY_ERROR was lost per call, and the 129th call hit "Unable to pull an error context from the array!" and exited the process. Every tilemap load resolves several paths this way, so a game that loaded fifty levels died in the loader.

    Fixed. The branch now records a flag and calls akgl_path_relative_root after FINISH. tests/util.c carries test_akgl_path_relative_releases_contexts, which resolves AKERR_MAX_ARRAY_ERROR * 2 paths through that branch and asserts the pool is where it started; against the old code that test does not fail, it terminates the suite.

    This is the only return from inside a HANDLE block in src/ — the other candidates use SUCCEED_RETURN, which releases correctly. Worth a grep before anyone writes a new one, and worth a line in AGENTS.md's error-handling protocol, which warns about *_RETURN inside ATTEMPT but not about returning out of HANDLE.

29. akgl_tilemap_load leaks five pooled strings per load. Measured by counting non-zero HEAP_STRING refcounts across load/release cycles: five per cycle, exactly, and akgl_tilemap_release gives none of them back. The 52nd map load in a process finds the pool empty.

    Blast radius: every level transition. A game with fifty levels, or one that reloads a level on death, hits it. The fix is a sweep of the loader's CLEANUP blocks — akgl_tilemap_load, akgl_tilemap_load_layers, akgl_tilemap_load_layer_tile, akgl_tilemap_load_layer_objects, and akgl_tilemap_load_tilesets_each all claim scratch strings — and it wants a test that asserts the pool is unchanged across a load/release cycle. That is its own commit, not a footnote to a benchmark.

    Until it is fixed, the tilemap-load benchmark in tests/perf_render.c reclaims the pool by hand between iterations, and says so.

30. Two JSON accessors turn string-pool exhaustion into a segfault. akgl_get_json_string_value ends its ATTEMPT with FINISH(errctx, false) at src/json_helpers.c:89, so a failed akgl_heap_next_string is swallowed rather than passed up, and src/json_helpers.c:91 then strncpys AKGL_MAX_STRING_LENGTH bytes through the pointer it never set. akgl_get_json_array_index_string has the same pair at src/json_helpers.c:143 and src/json_helpers.c:145. Item 29 is what makes this reachable, and this is what item 29 looks like from the outside: not AKGL_ERR_HEAP, a crash inside strncpy with a NULL destination.

    Fix: FINISH(errctx, true) in both. One word each, but it changes what callers see on a path they currently cannot survive, so it wants a test that exhausts the pool deliberately and asserts AKGL_ERR_HEAP comes back out of both functions.

31. akgl_game_update segfaults if akgl_game_init did not run. src/game.c:182 calls game.lowfpsfunc() through the pointer with no NULL check, on every frame where game.fps is under 30 — which includes the first frame, before there is a frame rate to compare against. akgl_game_init installs the default; nothing else does.

    That matters because include/akgl/renderer.h documents the other path on purpose: a host that owns its own window and calls akgl_render_bind2d instead of akgl_render_init2d. An embedder following that documentation and then calling akgl_game_update crashes on frame one. akbasic is exactly that embedder.

    Fix: guard the call, or have akgl_game_updateFPS install the default when it finds a NULL. tests/perf_render.c installs it by hand as a workaround and points here.

32. akgl_game_update runs the actor update sweep once per tilemap layer. src/game.c:617 loops i over AKGL_TILEMAP_MAX_LAYERS and the actor sweep nested inside it never compares actor->layer to i, so every live actor's updatefunc runs 16 times per frame. Measured: 68.4 ns per update, 64 actors, so 70 µs of work to do 4.4 µs of work.

    It hides behind the rasterizer today (a 640x480 software frame is 16 ms) and it will not hide behind a GPU backend, where a frame is nearer 2 ms and this is 3.5% of it. Fix: either filter by layer like akgl_render_2d_draw_world does, or hoist the update sweep out of the layer loop entirely — updating an actor is not a per-layer operation. The second is almost certainly right, and it is the one that needs a test asserting updatefunc runs exactly once per actor per akgl_game_update.

33. akgl_heap_release_character leaks its state_sprites property set. Fixed in 0.5.0; see item 21, which is the same defect. The character-load benchmark in tests/perf_render.c was written around it and no longer has to be.

Targets

What a library like this should hit. These are not predictions of what the current code does — several are missed today, and each says which. The frame budget throughout is 16.67 ms (60 fps); where a target is stated per-operation it is because that is the number that survives a change of renderer.

The one that governs the rest: libakgl's own bookkeeping should never be the reason a frame is late. Everything the library decides — pool scans, registry lookups, state-to-sprite mapping, physics, visibility, error contexts — should fit in 5% of a frame, leaving 95% for the pixels and the game's own logic. At 64 actors and a screenful of tiles that is a ceiling of about 800 µs.

#	Target	Today	Verdict
1	Library bookkeeping under 5% of a 60 fps frame at 64 actors + 1200 tiles	~0.3% (excluding pixel work)	met
2	One actor's logic update under 200 ns	68.4 ns	met
3	One actor's render bookkeeping, excluding the blit, under 500 ns	~250 ns, by subtraction rather than direct measurement	met, weakly measured
4	Physics sweep under 25 ns per live actor, and proportional to live actors rather than pool size	19 ns per live actor, but 63.9 ns for an empty pool	partly
5	Tilemap draw bookkeeping under 100 ns per tile, excluding the blit	~25 ns	met
6	Pool acquire under 100 ns regardless of how full the pool is	3.9 ns empty, 250.9 ns on the last free string slot	missed
7	Pool release proportional to the bytes actually used, not to the slot's capacity	47.2 ns, a fixed 4 KiB wipe	missed
8	Re-drawing an unchanged line of text under 1 µs	12.6 µs, every frame, no cache	missed
9	Zero texture creation or destruction per frame in steady state	one create + one destroy per line of text per frame	missed
10	A handled, routine condition costs no more than twice the path that succeeds	616.5 ns vs 68.4 ns — 9x	missed
11	256 actors simulated, updated and made ready to draw in under 1 ms	~22 µs at 64 actors (5.8 µs measured logic + estimated render bookkeeping); linear, so ~90 µs extrapolated	met, untested at that size
12	Collision for 256 actors under 2 ms without the caller writing a broad phase	no broad phase exists; the naive loop is 1.9 ms at 256 actors	missed
13	Level load under 100 ms for a map with 8 tilesets, 4 layers and 64 actors	11.9 ms for a 2x2 map with one tileset	unknown at that size
14	Fixed per-load overhead under 1% of a level load	11.5% — zeroing 26 MB of akgl_Tilemap	missed
15	Static footprint under 4 MB in the default configuration	28 MB, 94% of it one tilemap	missed
16	No pool leaks across a load/release cycle of any asset type	tilemap leaks 5 strings per cycle (item 29)	missed
17	Pool exhaustion reports AKGL_ERR_HEAP and never crashes	item 30 crashes	missed
18	Every benchmark held to 10x its recorded baseline, enforced in CI	done, ctest -L perf	met

Notes on the ones worth arguing about:

• 6 and 7 are the same fix. The acquire scan is 64x slower on a full string pool than an empty one purely because the pool is a megabyte and the scan touches one refcount per 4 KiB. A free-list index — one int per layer, remembering where the last free slot was — takes both to constant time without changing the "no malloc" rule at all. That is the change I would make first, and it is worth doing before anyone raises AKGL_MAX_HEAP_*, because the cost of the current design grows with the ceiling rather than with the usage.

• 8 and 9 are one cache. A single entry keyed on (font, string, colour, wrap) would cover the common case — a HUD field that changes once a second — and a four- or eight-entry ring would cover the rest. This is the clearest optimisation in the library and it is maybe forty lines.

• 10 is a design target, not a speed target. The answer is not a faster error context. It is that "this character has no sprite for this state" is a question with a boolean answer, and reporting it through AKERR_KEY costs nine times the update it replaces. akgl_character_sprite_get wants a companion that returns NULL without raising.

• 12 is a scope decision, not a defect. The library deliberately does not own a broad phase, and at 64 actors the naive all-pairs loop is 0.7% of a frame — genuinely fine. At 256 it is 11%. Either the ceiling stays where it is and this target is dropped, or a uniform grid keyed on tile size goes in. I do not think a spatial index belongs here yet; I think the target belongs on record so that raising AKGL_MAX_HEAP_ACTOR is a decision made with the number in front of it.

• 14 and 15 are the same fix too. akgl_Tilemap is 26 MB because every layer carries a 512x512 int grid and every tileset a 65,536-entry offset table, sized for the worst case at compile time. The pool rule does not require this: a layer could carry an index into one shared cell arena sized by AKGL_TILEMAP_MAX_WIDTH * AKGL_TILEMAP_MAX_HEIGHT once rather than sixteen times, and the offset table could be sized by tilecount rather than by the maximum. That is a real refactor with a real ABI break, so it belongs to 0.4 rather than to a patch release — but 28 MB of BSS on a handheld or an ESP32-class target is the difference between fitting and not.

• 13 is untested and should not stay that way. The only map fixture in the tree is 2x2 with one tileset, which is why the load benchmark measures a PNG decode and a memset rather than a map. A realistic fixture — 128x128, four layers, several tilesets — would make target 13 measurable and would probably find something.

Memory checking

cmake --build build --target memcheck runs the suites that already exist under valgrind — ctest -T memcheck with the headless drivers forced, wrapped by scripts/memcheck.sh so that a finding is an exit status rather than a line in a log nobody reads. There are no memory-check test programs, and there should never be any: tests/benchutil.h notices that it is running under valgrind and divides every benchmark's iteration count by two thousand, which turns the perf suites into the broadest path coverage in the tree at a cost valgrind can survive. The whole run is about thirty seconds.

The two halves fit together on purpose. A benchmark is a program that walks one path a hundred thousand times; a leak check wants every path walked once. Same binaries, same registration, one flag apart.

Third-party findings are suppressed in scripts/valgrind.supp, and the run forces SDL_VIDEO_DRIVER=dummy / SDL_RENDER_DRIVER=software / SDL_AUDIO_DRIVER=dummy so the vendor GPU stack is never loaded — that removes thousands of unfixable findings inside amdgpu_dri.so without suppressing anything at all. Only definite losses and invalid accesses are counted; "still reachable" is what SDL and FreeType keep for the process lifetime and says nothing about this library.

Defects the memory checker found

All six are fixed. They are kept here rather than deleted because the sizes are measured and the reasoning is worth having next time somebody asks why a loader ends in a CLEANUP block, or why a name field is staged through a zeroed buffer. cmake --build build --target memcheck is clean, and the CI job that runs it gates: the next one of these fails the build on the push that introduces it.

Ordered by blast radius as they were found. Numbering continues the lists above. Every size below is measured, not estimated.

34. Every JSON loader leaks its parsed document. There are four json_load_file calls in src/ and not one json_decref anywhere in the library, so the whole parsed tree — objects, hashtables, strings — is abandoned on both the success and failure paths:

    Loader	Site	Leaked per call
    akgl_sprite_load_json	src/sprite.c:140	~1,500 bytes
    akgl_character_load_json	src/character.c:232	~2,150 bytes
    akgl_tilemap_load	src/tilemap.c:693	~9,000 bytes (2x2 fixture map)
    akgl_registry_load_properties	src/registry.c:134	not exercised by any test

    Blast radius: every asset load, forever. The map figure is for the 2x2 fixture; a real map's JSON is the size of its layer data, so a 128x128 map leaks on the order of a megabyte per load. A game that reloads a level on death leaks a level's worth of JSON each time, and this is the one item in this list that grows without bound.

    Fixed. json_decref in the CLEANUP block of each, on the success path as well as the failure one, with the handle nulled after so a second pass cannot double-release. akgl_registry_load_properties needed its loop moved inside the ATTEMPT block first: props is a borrowed reference into the document and was read after the block ended, so every exit from that loop leaked the document. The test is the memcheck run -- nothing in the public API can observe a jansson refcount, and inventing a hook to prove it would be testing the test.

35. akgl_get_property reads up to 4 KiB past the end of the property value. src/registry.c:181 copies a fixed AKGL_MAX_STRING_LENGTH bytes out of whatever SDL_GetStringProperty returns, and what it returns is an SDL_strdup of the value — four bytes for "0.0". Valgrind reports an invalid read on every call, twelve of them in tests/physics.c alone, because akgl_physics_init_arcade reads six properties and akgl_render_init2d reads two more.

    This has been in registry.h as a @note about the copy being "a fixed #AKGL_MAX_STRING_LENGTH bytes rather than the length" — filed as waste. It is not waste, it is an out-of-bounds read: today it walks into the rest of SDL's heap and returns garbage past the terminator, and on a value that lands at the end of a page it is a segfault in a getter.

    Fixed. The copy is bounded by the value's own length plus its terminator, and a value too long for an akgl_String is now refused with AKERR_OUTOFBOUNDS instead of silently truncated. The documented AKERR_NULLPOINTER for "unset with no default" is unchanged -- it is raised deliberately now rather than arriving from inside aksl_memcpy. tests/registry.c fills the destination with a sentinel, reads a three-byte property back, and asserts every byte past the terminator still holds the sentinel; that assertion fails against the old code.

36. The savegame name tables read past the end of every registry key, and write what they find into the file. akgl_game_save_actorname_iterator (src/game.c:219) writes AKGL_ACTOR_MAX_NAME_LENGTH — 128 — bytes starting at the key SDL handed it, and SDL allocated that key to fit the name. Valgrind catches it on a 40-byte allocation. The three sibling iterators do the same thing at src/game.c:248, src/game.c:280 and src/game.c:308, with 128, 512 and 128 byte fixed widths; only the actor one is reached by the current tests, because the other registries are empty in the save roundtrip.

    Two consequences, and the second is the interesting one. The read can fault if the key sits at the end of a page. And whatever it reads goes into the save file, so a savegame contains up to 500 bytes of this process's heap per registered object — anything that happened to be next to the key. That is a file a player might send someone.

    Fixed. All four iterators now write through write_name_field, which stages the key into a zeroed fixed-width buffer, so the padding is deterministic and nothing but the name leaves the process. A negative-array-size typedef fails the build if any of the four widths ever outgrows the staging buffer. Still open and unrelated to the overread: Defects -> Known and still open item 7, the same tables disagreeing about their widths between writer and reader.

37. akgl_controller_list_keyboards leaks the array SDL gives it. src/controller.c:188 calls SDL_GetKeyboards, which allocates, and never calls SDL_free on the result. Four bytes per call in the test environment — one keyboard id — but it is per call, and the function is shaped like something a game calls when a device is hotplugged.

    Fixed. One SDL_free, in a CLEANUP block so a failure inside the loop cannot take the array with it. Still worth asking the same question of every SDL enumeration in src/controller.c: SDL_GetGamepads has the same contract, and the dummy driver reports no gamepads, so no test reaches it.

38. A font, once loaded, is never freed and cannot be. akgl_text_loadfont (src/text.c:20) opens a TTF_Font, puts the pointer in AKGL_REGISTRY_FONT, and that is the last anyone can do about it: the header exposes no way to close a font, and SDL_Quit destroying the property registry drops the last reference. 10,523 bytes per font — 736 of them SDL_ttf's, the rest FreeType's.

    This is bounded by how many fonts a game loads, so it is not the runaway that item 34 is. It was a gap in the API rather than only a leak: a game that switches fonts between scenes, or a tool like charviewer that reloads one while the user picks a size, had no way to give the old one back.

    Fixed, and this one is a new public symbol rather than a repair: akgl_text_unloadfont(char *name) clears the registry entry and closes the font. akgl_text_loadfont calls it when it replaces a live name, which closes the second leak the header used to document as intended behaviour -- but only after the new font has opened, so a failed reload leaves the caller with the font they already had. The version goes to 0.4.0 with it: an 0.3 consumer cannot be handed this library and told it is the same ABI.

    Still open: nothing closes the registry's remaining fonts at shutdown. A game that exits without unloading leaks them exactly once, which valgrind reports against the process rather than against a loop, and which akgl_game_shutdown would be the natural home for if it existed.

39. Vendored deps/semver's own unit test leaks 188 bytes across 16 blocks, from the callocs in test_strcut_first and test_strcut_second (deps/semver/semver_unit.c:8 and :21). Not libakgl's code and not libakgl's to fix; recorded so that nobody re-diagnoses it, and because semver_unit is registered as one of our CTest tests and so shows up in our memcheck run.

    Suppressed, which is what this list said the answer would be if it ever became noise, and gating the job made it noise. The two entries in scripts/valgrind.supp name the functions rather than the file, so a rewrite of those cases stops being suppressed and comes back as a finding. They are the only entries there that hide a real leak in a program this build runs; the alternative was a fork of a vendored dependency.

Not defects, and why

• tests/util.c fixtures were reading uninitialised stack floats. Three null-pointer tests declared SDL_FRect and point fixtures without initializing them and then made one real call with them at the end, which is sixteen "conditional jump depends on uninitialised value" findings for a test that is not about coordinates. The fixtures are zeroed now. The library was never at fault; a memory checker that reports noise gets ignored, which is the only reason this was worth touching.
• "Still reachable" at exit is not counted. SDL's global state, the hint table, the property registry and FreeType's library instance are one per process and are reclaimed by SDL_Quit / TTF_Quit. Counting them would bury the six findings above under a hundred that mean nothing.
• The GPU driver's findings are avoided rather than suppressed. Running the suite against the real driver produces thousands of findings inside amdgpu_dri.so; running it headless produces none, and headless is what the suites are written for anyway.

Found while embedding libakgl in a consumer

40. Shadowing add_test() unconditionally broke every embedding consumer. Fixed in the same release it was introduced in, and worth keeping because the CMake behaviour behind it is not obvious and will catch the next person.

    18399f2 moved the vendored-dependency block out from behind if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR) — which was the point of that commit — and took the add_test()/set_tests_properties() override out with it. The override's own comment claimed "an embedding consumer's add_test() still reaches CTest". It does not, and cannot.

    CMake chains command overrides exactly one level deep. Overriding add_test makes the builtin available as _add_test; overriding it a second time rebinds _add_test to the first override and the builtin becomes unreachable to everybody, permanently — there is no __add_test. Verified directly rather than inferred from the documentation:

    function(add_test) _add_test(${ARGV}) endfunction()   # _add_test  -> builtin
    function(add_test) _add_test(${ARGV}) endfunction()   # _add_test  -> the first override
    if(COMMAND __add_test) ... endif()                    # absent
    

    So two projects in one tree cannot both shadow it. akbasic shadows it first — it has to, for libakerror and libakstdlib, which register their tests unconditionally — and its own registrations then recursed until CMake stopped at "Maximum recursion depth of 1000 exceeded". A consumer had no way to work around it: once the builtin is gone it is gone for that project too.

    Fix: the override is guarded on being top-level again, exactly as it was before 18399f2 and exactly as libakstdlib guards its own. The vendored-dependency block stays unconditional, which is what that commit was actually for. An embedded libakgl leaves add_test alone and lets its consumer suppress what it does not want — machinery the consumer has to have anyway.

Build notes

The vendored SDL satellite libraries are built into per-project subdirectories that are not on the loader's default search path, and LD_LIBRARY_PATH is searched ahead of RPATH — so a developer who has previously run rebuild.sh had their installed libakgl.so shadow the one under test, and a developer who had not saw every test abort before main() with "cannot open shared object file". CMakeLists.txt now sets BUILD_RPATH on the library, the utility, and every test target, and prepends the build tree to LD_LIBRARY_PATH for the CTest run.

API gaps blocking akbasic

akbasic (the C port of the BASIC interpreter, source.starfort.tech/andrew/akbasic) is being built to link into libakgl as a scripting engine for game authors.

All ten items are resolved. Items 1 through 4 landed first and akbasic has since consumed every one of them: its libakgl-backed text sink, its graphics backend, its sound backend and its input backend are written and tested, and the BASIC 7.0 graphics verbs (GRAPHIC, COLOR, DRAW, BOX, CIRCLE, PAINT, SCALE, SSHAPE, GSHAPE, LOCATE), the sound verbs (SOUND, ENVELOPE, VOL, PLAY, TEMPO) and the console input verbs (GET, GETKEY, SCNCLR) all work against them.

Doing that turned up items 5 through 9. Four were things akbasic had to work around to build at all; each workaround is commented at its site over there with the words "filed upstream". Those workarounds can now be deleted — including the five add_subdirectory lines for the vendored SDL projects and the hand-assigned render vtable in tests/akgl_backends.c.

Building the standalone SDL frontend on top of all that — a real window, a real event pump and a line editor — turned up item 10, and re-confirmed items 6 and 7: both workarounds had to be written a second time, in src/frontend_akgl.c, because a host that owns a window is exactly the caller they inconvenience.

These were filed here rather than worked around in akbasic because growing libakgl to serve a consumer is the wanted outcome. Each entry says what the BASIC verb needs, what the akgl_* entry point should look like, and what would cover it.

Items 7, 9 and 10 add public symbols and item 9 adds three fields to akgl_AudioVoice, so the project version goes to 0.3.0 and the soname with it — an 0.2 consumer cannot be handed this library and told it is compatible.

1. No way to measure rendered text. include/akgl/text.h exposes akgl_text_loadfont() and akgl_text_rendertextat(), and nothing that reports how large a string will be in a given font. A terminal-style text surface cannot be built on that: a cursor needs the advance width of one cell, and wrapping needs to know where a string crosses the right margin. The reference interpreter got this from SDL2_ttf's font.SizeUTF8("A") and derived its whole character grid from it.

   Wants akerr_ErrorContext AKERR_NOIGNORE *akgl_text_measure(TTF_Font *font, char *text, int *w, int *h); over TTF_GetStringSize, and probably a companion akgl_text_measure_wrapped(font, text, wraplength, w, h) matching the wraplength argument akgl_text_rendertextat already takes. Tests: a known string in a known font at a known size, the empty string, and a wrapped string wide enough to force two lines.

   This is the only one of the four that blocks work already designed and waiting. akbasic cannot render any output through libakgl until it lands.

   Resolved. akgl_text_measure(font, text, w, h) and akgl_text_measure_wrapped(font, text, wraplength, w, h) are in include/akgl/text.h, over TTF_GetStringSize and TTF_GetStringSizeWrapped. Neither needs a renderer. A negative wraplength is refused with AKERR_OUTOFBOUNDS rather than passed through, because SDL_ttf reads it as a very large unsigned width and silently stops wrapping. tests/text.c covers both against tests/assets/akgl_test_mono.ttf, a 10 KB monospaced ASCII subset added for the purpose — being monospaced, it lets the suite assert width("AAAA") == 4 * width("A") instead of hardcoding glyph metrics that FreeType is free to round differently. Same change fixed item 39 below: akgl_text_loadfont checked name twice and never checked filepath.

2. No immediate-mode drawing. include/akgl/draw.h declares exactly one function, akgl_draw_background(int w, int h), and src/draw.c is at 0% coverage. BASIC 7.0's graphics verbs are all immediate-mode plotting against the current screen: DRAW (line and point), BOX, CIRCLE, PAINT (flood fill), LOCATE (set the pixel cursor), COLOR, and SSHAPE/GSHAPE (save and restore a rectangle of pixels).

   Wants an akgl_draw_* family taking the renderer the host already initialized -- akgl_draw_line, _rect, _filled_rect, _circle, _point, _flood_fill, _copy_region -- in the shape of the existing akgl_render_2d_draw_texture. SDL3's SDL_RenderLine/SDL_RenderRect/SDL_RenderFillRect cover most of it; the circle and the flood fill do not exist in SDL3 and need writing. Tests belong with the offscreen renderer harness described under "Remaining work": render a known shape, read the target back, and compare against a reference surface with the existing akgl_compare_sdl_surfaces.

   Resolved. include/akgl/draw.h now declares akgl_draw_point, _line, _rect, _filled_rect, _circle, _flood_fill, _copy_region and _paste_region, all taking the akgl_RenderBackend * the host initialized, in the shape of akgl_render_2d_draw_texture. Decisions worth knowing:

   • Color is an argument, not state. There is no current-color global to get out of step with the caller's own. Each call saves and restores the renderer's draw color, so drawing a line does not change what the host's next SDL_RenderClear paints. tests/draw.c asserts that.
   • The circle is a midpoint circle, integer arithmetic with eight-way symmetry, plotted eight points per step through SDL_RenderPoints.
   • The flood fill reads the target back, fills on the CPU, and blits only the bounding box of what changed. It keeps a fixed AKGL_DRAW_MAX_FLOOD_SPANS (4096) stack of horizontal runs at file scope rather than recursing per pixel; running out reports AKERR_OUTOFBOUNDS and leaves the region partially filled, which is stated in the header. It is therefore not reentrant — neither is anything else that draws to a single SDL_Renderer.
   • _copy_region allocates when *dest is NULL and otherwise copies into the caller's surface, matching akgl_get_json_string_value and friends. A region that would be clipped by the target edge is refused rather than silently returning a smaller surface.

   tests/draw.c draws into a 64x64 software renderer under the dummy video driver and reads pixels back, so it did not need the offscreen harness. That harness is still wanted for src/renderer.c, src/text.c and src/assets.c. akgl_draw_background is untouched and still outside the error protocol (item 35).

3. No audio API at all. SDL3_mixer is a vendored dependency and registry.h declares AKGL_REGISTRY_MUSIC, but there is no src/audio.c, no include/akgl/audio.h, and no akgl_* symbol that opens a mixer, loads a chunk, or plays a note. BASIC 7.0's sound verbs are SOUND (a tone on a voice, with a duration), PLAY (a string of notes in a Commodore-specific notation), ENVELOPE (ADSR per voice), FILTER, VOL and TEMPO.

   PLAY and ENVELOPE want a synthesised voice rather than a sample, which SDL3_mixer does not provide directly -- the honest first step is a small tone generator feeding SDL_AudioStream, with akgl_audio_init, akgl_audio_tone(voice, hz, ms), akgl_audio_envelope(voice, a, d, s, r) and akgl_audio_volume(level). This is the largest of the four and the one most worth designing before writing. Tests can run under the dummy audio driver and assert state transitions rather than sound.

   Resolved. include/akgl/audio.h and src/audio.c add a three-voice tone generator over SDL_AudioStream: akgl_audio_init, _shutdown, _tone, _stop, _waveform, _envelope, _volume, _voice_active and _mix. It is deliberately separate from the SDL3_mixer side of the library, which plays audio assets; nothing in audio.c reads a file. Decisions worth knowing:

   • The voice table works with no device open. akgl_audio_init connects it to one; without that a host can still pull samples itself through akgl_audio_mix. That is not only for embedding — it is what makes the suite deterministic. A device pulls samples on SDL's audio thread whenever it likes, so a test that opened one and then asserted on voice state would be racing the callback. tests/audio.c mixes by hand and opens a device only in its last test.
   • Phase is derived from the frame counter, not accumulated. A float increment of hz / 44100 is not exact, and adding it 44100 times a second walks a held note off pitch.
   • A voice that was never configured is audible. A zeroed voice has a sustain of 0.0, which is silence with no error to explain it, so the table defaults to a square wave held at full level.
   • Three voices summing past full scale are clamped, not scaled, so one voice plays at the level it was asked for rather than a third of it.
   • Everything that touches the table takes the stream lock when a device is open, since the callback reads it on another thread.

   Still missing for a complete BASIC sound vocabulary: FILTER (SDL3 has no filter primitive; this would need writing), TEMPO and the PLAY note-string parser, both of which belong in the interpreter rather than here.

4. No non-blocking keystroke read. include/akgl/controller.h is built around SDL event handlers the host pumps (akgl_controller_handle_event and friends), which suits a game loop and does not suit GET and GETKEY -- those ask "is there a keystroke waiting, yes or no" and must not require the interpreter to own the event loop. Goal 3 of akbasic forbids it owning one.

   Wants akerr_ErrorContext AKERR_NOIGNORE *akgl_controller_poll_key(int *keycode, bool *available); reading a small ring buffer that akgl_controller_handle_event already fills, so the host keeps pumping events and the interpreter drains characters at its own pace. Tests: push synthetic SDL_EVENT_KEY_DOWN events through the existing handler and drain them, plus the empty-buffer and overflow cases.

   Resolved. akgl_controller_poll_key(int *keycode, bool *available) and akgl_controller_flush_keys(void) are in include/akgl/controller.h, over a fixed AKGL_CONTROLLER_KEY_BUFFER (32) ring in src/controller.c. akgl_controller_handle_event records every SDL_EVENT_KEY_DOWN before it scans the control maps, so a key bound to an actor still reaches a polling caller — the scan returns as soon as a binding claims the event, and doing it afterwards would have lost exactly the keys a game also acts on. An empty buffer is success with available false, not an error. A full buffer drops the newest key rather than overwriting the oldest, matching the Commodore keyboard buffer and keeping what was typed first. tests/controller.c covers drain order, the release-is-not-a-keystroke case, a key shared with a control map, flush, both NULL arguments, and overflow plus reuse afterwards.

5. An embedded libakgl demands its dependencies be installed, while vendoring them. CMakeLists.txt:17 gates the whole vendored-dependency block on CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR, so deps/SDL, deps/SDL_image, deps/SDL_mixer, deps/SDL_ttf and deps/jansson are added only when this repository is the top-level project. Embedded with add_subdirectory(), the else() branch at :51 runs find_package(SDL3 REQUIRED) and friends instead, and configure fails on a machine that has none of them installed — with the submodules sitting right there in deps/, already checked out by the recursive clone the consumer just did.

   akbasic works around it by adding those five subdirectories itself, immediately before add_subdirectory(deps/libakgl). That works only because every lookup in the else() branch is guarded with if(NOT TARGET ...) — which is the same escape hatch akerror::akerror and akstdlib::akstdlib already rely on, and it should not be the documented answer. Fix: add the vendored dependencies on both paths, still guarded by if(NOT TARGET ...) so a consumer that has already declared them wins. The suppression of their CTest registration should move with them.

   Resolved. The vendored block no longer sits behind CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR. An akgl_add_vendored_dependency(<target> <dir>) macro adds each of the seven submodules when nothing has already declared that target and the submodule is actually checked out; the find_package lookups for anything left over run afterwards, unchanged, so a checkout without submodules still resolves against the system. A macro rather than a function because add_subdirectory() inside a function runs in that function's variable scope.

   The CTest suppression moved with them, and is lifted again before this project registers its own suites, so an embedding consumer's add_test() still reaches CTest. Two smaller consequences of the move: find_package(PkgConfig) now runs only when something has to come from the system (a fully vendored build needs no pkg-config of its own, though deps/SDL_mixer asks for it separately), and the build-tree RPATH block keys on whether anything was vendored rather than on being the top-level project, so an embedded build's tests can also find the satellite libraries.

   Verified by configuring and building a scratch consumer that embeds this repository with CMAKE_DISABLE_FIND_PACKAGE_SDL3, _SDL3_image, _SDL3_mixer, _SDL3_ttf, _akerror, _akstdlib and _jansson all set, so any reliance on an installed copy would have failed the configure. It configures, builds and links. The five add_subdirectory lines in akbasic's CMakeLists.txt can be deleted.

6. include/akgl/controller.h does not compile on its own. Lines 35, 36 and 41 declare handler function pointers taking an akgl_Actor *, and the header includes only SDL3/SDL.h, akerror.h and types.h — none of which declares that type. Any translation unit that includes akgl/controller.h before akgl/actor.h fails with "unknown type name 'akgl_Actor'". src/controller.c never notices because it includes akgl/game.h first.

   This is the house rule in AGENTS.md — keep headers self-contained, include what you use. Fix: #include "actor.h" in controller.h, or forward-declare struct akgl_Actor if the include order makes that circular. A one-line test that includes only akgl/controller.h would have caught it and would keep catching it.

   Resolved. controller.h includes <akgl/actor.h>. Not a forward declaration: akgl_Actor is a typedef of a named struct, and repeating a typedef is C11, not C99. The include closes no cycle — actor.h reaches only types.h and character.h, neither of which knows about the controller.

   tests/headers.c is the test, and it is a whole suite for one #include on purpose: a second #include after the first proves nothing about the second, because by then the first has dragged its dependencies in. Covering another header means another file shaped like that one. It also stopped being true that tests/controller.c has to include akgl/actor.h first, and the comment there saying so is gone.

7. There is no way to attach a 2D backend to a renderer the caller already has. akgl_render_init2d() (src/renderer.c:17) does two separable things: it creates a window and an SDL_Renderer from the game.screenwidth/game.screenheight properties and writes to the camera global, and it installs the six function pointers that make an akgl_RenderBackend usable. A caller who already owns an SDL_Renderer wants only the second half — and that caller is not hypothetical, it is precisely the embedding host the API-gap section above exists to serve, since an embedded interpreter must not create the window.

   Today the only options are to call akgl_game_init() and let libakgl own the window, or to assign the six pointers by hand, which is what akbasic's tests/akgl_backends.c does. Fix: split out akgl_render_bind2d(akgl_RenderBackend *self) that installs the vtable and nothing else, and have akgl_render_init2d() call it after it has made its window. tests/renderer.c could then cover the vtable half without a display at all.

   Resolved. akgl_render_bind2d(akgl_RenderBackend *self) installs the six pointers and returns; akgl_render_init2d() calls it once the window and the camera exist. It deliberately does not touch self->sdl_renderer, which is the whole point — a host that already owns one keeps it, and a host that does not gets a backend whose entry points all report AKERR_NULLPOINTER instead of crashing.

   tests/renderer.c is new and needs no display: it covers the binding (including that the caller's SDL_Renderer survives it, and that binding a backend without one is legal), frame start and end and both draw_texture paths against a software renderer under the dummy video driver, the refusals a bound-but-unrendered backend gives, and the draw_mesh "not implemented" stub. src/renderer.c goes from 10% line coverage to 56%; what is left is akgl_render_init2d itself and akgl_render_2d_draw_world, both of which want the offscreen harness and the world globals. akbasic's hand-assigned vtable in tests/akgl_backends.c can be deleted.

8. akgl_text_rendertextat() dereferences an uninitialised backend vtable. src/text.c calls renderer->draw_texture(renderer, ...) with no NULL check on either renderer or the function pointer, so a backend that has an SDL_Renderer but has not been through akgl_render_init2d() segfaults on the first line of text. That is exactly the state item 7 leaves a host in, and it is the same class of defect the draw commit at 42b60f7 added a test for — "a backend that exists but was never given an SDL_Renderer, which is the state a host is in between allocating one and initializing it; every draw entry point has to report it rather than dereference it." The text path still has it.

   Fix: FAIL_ZERO_RETURN on renderer, on renderer->sdl_renderer and on renderer->draw_texture, reporting AKGL_ERR_SDL or AKERR_NULLPOINTER as the draw entry points do. Test alongside the existing tests/draw.c backend-without-a-renderer case.

   Resolved. All three are checked, with AKERR_NULLPOINTER to match the draw entry points, and they are checked before anything is rasterized rather than after: refusing early costs nothing and leaks nothing, where refusing after the rasterize would hit the leak the @note on this function already describes.

   tests/text.c grew a software renderer under the dummy video driver — bound with the new akgl_render_bind2d, which is what made this cheap — and covers all three refusals plus the successful draw, wrapped and unwrapped. src/text.c goes from 58% to 100% line coverage, and the three akgl_text_rendertextat mutants the mutation run left surviving are dead. The third case is the one that matters: with a live SDL_Renderer behind a backend that was never bound, the old code got all the way to a NULL function pointer. Checking it against a made-up renderer pointer, as the first draft of the test did, is worth nothing — SDL refuses the bogus handle and the call fails for the wrong reason, which a deleted-check mutant survives.

   Found while writing that test and filed below as item 27: SDL_ttf refuses the empty string on both rasterizing paths, so drawing an empty line is an error while measuring one is not.

9. SOUND's frequency sweep has no akgl_audio_* equivalent. BASIC 7.0's SOUND voice, freq, dur, dir, min, step ramps the pitch from freq toward min in step increments per tick, in the direction dir selects — a siren, a laser, the whole reason SOUND has six arguments. akgl_audio_tone(voice, hz, ms) holds one pitch for one duration, and nothing changes pitch over the life of a note.

   akbasic refuses those three arguments rather than faking them, and the reasoning is worth recording because it is what makes this a libakgl gap rather than an interpreter one: the only way to fake a sweep from the interpreter is to re-issue tones from its step loop, which ties audible pitch to how often the host happens to call it — a tune that changes key with the frame rate. It has to be advanced on the mixer's own frame counter, which is where the phase is already derived from and which only this library can see.

   Fix: akgl_audio_sweep(int voice, float32_t from_hz, float32_t to_hz, float32_t step_hz, uint32_t ms), advanced in akgl_audio_mix() beside the envelope. Tests would drive akgl_audio_mix by hand and assert the frame at which the pitch has moved, exactly as tests/audio.c already does for the envelope stages.

   Resolved. akgl_audio_sweep(voice, from_hz, to_hz, step_hz, ms) is in include/akgl/audio.h, with the step taken in akgl_audio_mix() off the mixer's own frame counter. Decisions worth knowing:

   • One step every 1/60 second (AKGL_AUDIO_SWEEP_TICK_HZ), because that is the rate the machine this vocabulary comes from advanced its sweep at, and its tunes are written for it. It divides 44100 exactly, so a step boundary always lands on a whole frame — which is what lets the suite assert the exact frame the pitch moves on rather than a tolerance.
   • Direction comes from the two frequencies, not from the sign of the step. step_hz stays positive; to_hz below from_hz sweeps down. A negative step is refused rather than silently meaning something.
   • It arrives and holds. The last step is clamped to to_hz rather than overshooting, and equal frequencies are a legal held tone rather than an error, so a caller computing its own limits does not have to special-case them.
   • akgl_audio_tone is now the same start path with a step of 0, which is also what makes a voice reused for a plain tone stop sweeping. That is one function, start_note, rather than two copies of the same six assignments.
   • A swept voice accumulates its phase instead of deriving it from the frame counter. Deriving assumes a constant frequency; under a sweep it jumps the waveform at every step, which is an audible click. The drift the derived form exists to avoid is not something a note that is changing pitch anyway can be said to suffer from.

   tests/audio.c drives the mixer by hand: one tick's frames do not move the pitch, the next frame does, both directions clamp at their target, a gate shorter than the sweep cuts it off part way, and a plain tone on a swept voice stays put. src/audio.c holds at 92%.

   Still missing for a complete SOUND: the oscillating third direction (C128 dir 2), which is a re-issue on arrival rather than a third kind of sweep, and FILTER, TEMPO and the PLAY note-string parser as before.

10. The keystroke ring carries a keycode and nothing else, so Shift is invisible. akgl_controller_handle_event() (src/controller.c:104-105) pushes event->key.key into the ring and drops the rest of the event, and akgl_controller_poll_key(int *keycode, bool *available) hands back only that. Item 4 asked for a non-blocking keystroke read and got one; what it did not ask for, and what a line editor turns out to need, is which character the keystroke actually produced.

    akbasic has now built one — an INPUT and a REPL prompt drawn in the window, in src/sink_akgl.c — and the consequence is concrete: no shifted character is reachable, so ", !, (, ), : and ; cannot be typed at all, and lower case cannot be typed either. A BASIC line editor that cannot type a double quote cannot enter a string literal. The interpreter folds letters to upper case, which is what a C128 does anyway and is the right resolution for letters; it is not a resolution for punctuation, and there is nothing the caller can do about it because the modifier state was discarded two layers down.

    Note this is not solvable by the caller polling SDL_GetModState() at read time: by then the key is long released, and the whole point of a ring is that reads are decoupled from events.

    Fix: widen the ring entry to carry the modifier state and the composed text SDL already computes. Either

    typedef struct akgl_Keystroke {
        SDL_Keycode key;
        SDL_Keymod  mod;
        char        text[8];    /* UTF-8, from SDL_EVENT_TEXT_INPUT; "" for a non-printing key */
    } akgl_Keystroke;
    
    akerr_ErrorContext AKERR_NOIGNORE *akgl_controller_poll_keystroke(akgl_Keystroke *dest, bool *available);
    

    alongside the existing akgl_controller_poll_key(), which stays as it is so nothing breaks — a game asking "was the up arrow pressed" wants exactly what it already gets. Filling text means handling SDL_EVENT_TEXT_INPUT as well as SDL_EVENT_KEY_DOWN, which is the only correct way to get a character out of SDL anyway: it is what makes a keyboard layout, a compose key and a dead key work, none of which a keycode can express.

    Tests would push a shifted key-down plus its text-input event through akgl_controller_handle_event() and assert both the keycode and the composed character come back, mirroring what tests/controller.c already does for the plain ring.

    Resolved. akgl_Keystroke (keycode, SDL_Keymod, and eight bytes of UTF-8) and akgl_controller_poll_keystroke(akgl_Keystroke *dest, bool *available) are in include/akgl/controller.h; the ring now holds those instead of bare keycodes. akgl_controller_poll_key() is untouched from its caller's side. Decisions worth knowing:

    • The text is attached to the press that is still waiting for it, tracked by a flag rather than by "whatever entry is newest". Without the flag, a press dropped by a full buffer hands its text to some older key that happens to be sitting at the end of the ring — which is wrong in exactly the case where things are already going badly.
    • Text with no press behind it is buffered on its own, with a keycode of 0. An input method commit and a character finished by a dead key have no key press of their own, and a line editor wants the character regardless. akgl_controller_poll_key() discards those on the way past rather than reporting a keystroke with no key.
    • Oversized text is cut on a code point boundary. An IME can commit several characters at once and an entry holds one; truncating on a byte boundary would leave a partial UTF-8 sequence that nothing downstream can render.
    • SDL only sends SDL_EVENT_TEXT_INPUT while text input is started, so a host that wants text populated calls SDL_StartTextInput() on its window. Without it key and mod still arrive. That is documented on the function rather than left to be discovered.

    tests/controller.c covers the shifted-key case end to end (the " that started this), a non-printing key composing to nothing, a text-only entry through both pollers, text that outlived its own press, the code-point-boundary truncation, and both NULL arguments. src/controller.c holds at 91%.

Carried over

1. Make character-to-sprite state bindings release their references symmetrically. akgl_character_sprite_add() increments the sprite refcount for every state-map binding, but no corresponding removal API exists. Replacing a state binding also leaves the previous sprite's refcount incremented. When akgl_heap_release_character() drops the character refcount to zero, it clears the character registry entry and zeroes the structure without enumerating state_sprites, decrementing the bound sprites, or destroying the SDL property map. Implement binding removal/replacement so each removed binding releases exactly one sprite reference. On final character release, enumerate every remaining binding (the existing akgl_character_state_sprites_iterate() release path may be reusable), release each reference, destroy state_sprites, and then clear the character. Add tests for removal, replacement, duplicate sprite bindings across multiple states, and final character release.

   The final-release half is done in 0.5.0 — see Defects item 21. akgl_heap_release_character now enumerates every remaining binding, releases each reference, destroys state_sprites, and then clears the character, and akgl_character_state_sprites_iterate is covered by that path.

   Still open: removal and replacement. There is no API to unbind one state, and akgl_character_sprite_add still overwrites an existing entry without releasing the sprite it displaces (Defects item 20). A character that rebinds a state while alive still leaks one reference per rebind; teardown only gives back whatever the map happens to hold at the end. Wants akgl_character_sprite_del, a release of the displaced entry inside akgl_character_sprite_add, and tests for removal, replacement, and duplicate sprite bindings across multiple states.

2. An actor cannot be scaled per axis. akgl_Actor::scale is one float32_t applied to both dest.w and dest.h, so there is no way to express "twice as wide, the same height". The VIC-II has had separate x- and y-expand bits since 1982 and Commodore BASIC 7.0's SPRITE verb exposes both, so a BASIC interpreter drawing through libakgl cannot implement its own documented verb.

   Two shapes are plausible and the choice is a design decision rather than an obvious fix: add scale_x / scale_y and keep scale as a convenience that writes both, or replace scale outright and take the ABI break while the major version is still 0. The second is cleaner and the soname already carries MAJOR.MINOR.

   Related to defect 26, and reached the same way: akbasic's sprites are Commodore sprites, 24 wide and 21 high, and SPRITE n,,,,1 expands one axis. It works around both by installing its own renderfunc on each actor rather than patching around the library.