Andrew Kesterson
6553da812c
They read as design commentary: why a choice was made, what the previous state of the project was, which library defect a line works around. That is useful to somebody who already knows the library and useless to somebody trying to build a game, which is who a tutorial is for. Both chapters now open with a screenshot of what the reader is building and a numbered list of the steps to get there, and each step is its own section: what you are trying to achieve, the code that achieves it, and the two or three things about that code that are easy to get wrong. Chapter 20 starts from first principles -- what a sprite, a character, an actor and a tilemap are, and the four error macros -- and chapter 21 assumes it and covers what a top-down game adds. Where a line exists because of a defect, the line comes first and the defect comes after it, with a pointer to the TODO entry that will remove the need. A reader who is copying code should not have to read an apology before they can use it. The library's own history is gone from both. That belongs in the design chapters and in git. Two new docs_examples setups stage the tutorials' own art, so the sprite and character files a reader is shown are loaded exactly as printed rather than through a generic fixture. `json excerpt=` is new for the same reason: a Tiled object is now quoted out of the real map instead of being retyped. Excerpts across docs/ go from 91 to 137. 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.