Andrew Kesterson
149bee0c99
Two agents were given nothing but the chapter text and asked to build the game from it. Between them they named every place the chapters showed a fragment and called it an explanation. This closes those. Chapter 20 now shows what it previously only named: the whole ss_Game struct rather than a truncated one, SS_COIN_COUNT and SS_HAZARD_COUNT, ss_ActorData, the player and blob body rectangles, asset_path, hitbox, find_actor, respawn, both jump handlers, the control-map function head, the gamepad buttons, the blob's probe arithmetic, and a complete standalone CMakeLists rather than three lines out of one. It also names the library globals a reader is expected to use without declaring, lists all seven actor hooks rather than the two this game replaces, and says in order what each of the two hook functions ends up doing. Chapter 21 gains the same treatment: the header's includes and declarations, the textbox colours and their SDL_Color type, TTF_Font, the jrpg_Townsfolk row type, character_load in full, the player lookup, the frame loop, and per-file include tables for both games. Two claims were wrong and are corrected. "Each step is complete on its own" was not true of a cumulative tutorial. And the first argument to akgl_controller_handle_event is not a game-state word the dispatcher reads -- the header says nothing reads it and it is required only as a non-NULL token. Every step that produces code now ends with what the reader should see when they run it. Excerpts across docs/ go from 137 to 190. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01KzBDV2fqgnUAcqCKqKvc71
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 eight 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 seven 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. Collision | Shapes, masks, tiles as geometry, the response hook, and the two partitioners |
| 16. Input | Control maps, push-not-poll dispatch, the keystroke ring, gamepads |
| 17. Text and fonts | Loading, drawing, measuring, and the teardown order that matters |
| 18. Audio | The three-voice synthesizer, and the separate background-music path |
| 19. Utilities | Rectangle overlap, path resolution, the JSON accessors, static strings |
| 20. Tutorial: a 2D sidescroller | Thirteen steps from an empty directory to a game with gravity, a jump, coins and hazards. Start here |
| 21. Tutorial: a top-down JRPG | Thirteen more, for four-way movement, NPCs, a text box, a follower, and freezing the world |
| 22. Appendix | Every limit, every status, every configuration property |
If you are new, read chapter 20 first and read it in order. It builds a working game from
an empty directory and teaches the library as it needs each piece; chapter 21 assumes it.
Both 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. The picture at the top of each chapter is a frame
out of the game itself, regenerated by cmake --build build --target docs_game_figures.
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.