Andrew Kesterson
943bf4324e
The sidescroller's controls did nothing. `akgl_controller_handle_event` matched `event->key.which == curmap->kbid` exactly, with no way to say "whatever keyboard the player is typing on", so the game did the obvious thing and bound `SDL_GetKeyboards()[0]`. That cannot work. The id a key event *carries* is chosen by the video backend and is not required to be an id `SDL_GetKeyboards()` reports. On X11 without XInput2 every key event carries `SDL_GLOBAL_KEYBOARD_ID`, which is 0, while `SDL_AddKeyboard` registers the attached keyboard as `SDL_DEFAULT_KEYBOARD_ID`, which is 1; with XInput2 the events carry the physical slave device's `sourceid` while `SDL_GetKeyboards()[0]` may be the master. Either way the map matched nothing and every key press was dropped. A `kbid` or `jsid` of 0 now matches any device of that kind. 0 is safe to spend: SDL documents `which` as 0 when the source is unknown or virtual, and joystick ids start at 1, so no real device is 0. A non-zero id still matches only that device, which is what keeps two local players on two keyboards apart, and there is a test for that half too. `util/charviewer.c` already passed 0 and depended on the old behaviour by accident; it works under XInput2 now as well. Two reasons this shipped, both closed: - Every test in tests/controller.c dispatched an event whose id equalled the id the map was bound with, so none of them could see it. - The sidescroller's smoke test called the control handlers directly instead of dispatching events, so it passed against a control map that matched nothing. It now pushes synthetic events through akgl_controller_handle_event from a deliberately non-zero device id and fails if the press does not arrive. Verified by breaking the binding and watching the run exit non-zero. `test_controller_wildcard_device_ids` was written first and failed against the unfixed library with "a map bound to keyboard 0 ignored a key press from device 11", which is the whole reason to trust it now that it passes. The controls were documented, in one sentence. Chapter 19 has a proper table of them, and chapter 15 explains why not to reach for SDL_GetKeyboards(). The header said the match was exact and now says what it does. Co-Authored-By: Claude Code <noreply@anthropic.com> Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
The libakgl manual
libakgl is a C library for building 2D games on SDL3. It is not an engine: there is no
editor, no scripting layer, no inheritance and no runtime malloc. Behaviour attaches to a
struct as function pointers, objects come from fixed pools, and every call reports failure
through an error context you cannot silently ignore.
This manual teaches the library. It deliberately does not re-document its dependencies
— libakerror owns the error-handling protocol, SDL3 owns renderers and events, Tiled owns
the map format, jansson owns the JSON API. Each chapter says what libakgl adds or
constrains, shows what a caller actually writes, and links out for the rest. For
per-function reference, build the Doxygen output with doxygen Doxyfile.
| 1. Introduction | What libakgl is, what it refuses to be, the frame budget, and who owns which documentation |
| 2. Design philosophy | Bounded pools, pluggable backends, bit flags, name-based registries, one world at a time |
| 3. Getting started | Dependencies, add_subdirectory vs akgl.pc, and the smallest program that opens a window |
| 4. Errors and status codes | The status tables, what each code means here, and the traps that fail silently |
| 5. The heap | The five pools, akgl_heap_next_*, akgl_String, and why exhaustion usually means a missing release |
| 6. The registry | The eight registries, configuration properties, and the id-0 silent no-op |
| 7. The game and the frame | Startup order, akgl_game_update, the state lock, iterators, savegames |
| 8. Rendering | The backend vtable, the frame contract, cameras, and embedding a host's own SDL_Renderer |
| 9. Drawing | Points, lines, rectangles, circles, flood fill, and saving a region |
| 10. Spritesheets and sprites | One texture shared by path, the sprite JSON format, frame animation |
| 11. Characters | State-to-sprite mappings, movement constants, the character JSON format |
| 12. Actors | The state bitmask, the six behaviour hooks, parents and children, layers |
| 13. Tilemaps | Tiled TMJ, libakgl's three extensions, and the limits that bind a map |
| 14. Physics | Thrust, environment and velocity; the null and arcade backends; what is not implemented |
| 15. Input | Control maps, push-not-poll dispatch, the keystroke ring, gamepads |
| 16. Text and fonts | Loading, drawing, measuring, and the teardown order that matters |
| 17. Audio | The three-voice synthesizer, and the separate background-music path |
| 18. Utilities | Collision helpers, path resolution, the JSON accessors, static strings |
| 19. Tutorial: a 2D sidescroller | Gravity, a jump, collision you write yourself, coins and hazards |
| 20. Tutorial: a top-down JRPG | A town map, NPCs spawned from map objects, four-way animation, a text box, a follower |
| 21. Appendix | Every limit, every status, every configuration property |
Both tutorials are complete programs under examples/. They build with the
library and run headless in CI, and the chapters quote them rather than restating them — so
a tutorial cannot drift from a program that compiles.
Every example here is checked
The examples in these chapters are compiled, linked, run, and cross-checked against the
source tree by the test suite. A snippet that stops compiling, an excerpt that no longer
matches the header it quotes, or a JSON document the loader would reject turns
ctest -R docs_examples red.
This exists because the documentation it replaces had drifted badly: the previous FAQ's
examples did not compile — two unbalanced PASS() calls, a sprite->frameids = [0, 1, 2, 3];
that is not C in any dialect, and, in the first snippet a reader ever saw, the exact
strncpy call AGENTS.md forbids. The prose had drifted with it, and writing these
chapters turned up twenty-seven header claims that were false against src/.
Where a chapter documents behaviour that is a known defect rather than a design decision,
it says so and points at TODO.md. See MAINTENANCE.md if you are editing an example.
Assets
The tutorial art, tiles and music are CC0, vendored under
tutorials/assets/ with provenance recorded per file in
PROVENANCE.md and geometry documented in
README.md. CC0 specifically, not merely free: a reader who
copies a tutorial into their own game inherits no obligation.