How do I initialize a game

Initialize the global game object with info about your game

	strncpy((char *)&game.name, "sdl3-gametest", 256);
	strncpy((char *)&game.version, "0.0.1", 32);
	strncpy((char *)&game.uri, "net.aklabs.games.sdl3-gametest", 256);

Call the game initialization routines and lock the game state for further initialization

PASS(e, akgl_game_init());
PASS(e, akgl_game_state_lock());

If you have a registry properties file, load it. If you don't have a properties file, use akgl_set_property("prop_name", "prop_value") to populate the required game properties.

PASS(e, akgl_registry_load_properties(YOUR_REGISTR_FILEPATH));

Initialize your physics engine and renderer of choice

PASS(e, akgl_render_2d_init(akgl_renderer));
PASS(e, akgl_physics_init_arcade(akgl_physics));

Unlock the game state

PASS(e, akgl_game_state_unlock());

What is in a properties file (or, What properties must I set if I don't have one?)

{
    "properties": {
		"game.screenwidth": "640",
		"game.screenheight": "480",
		"physics.gravity.y": "1024.0",
		"physics.drag.y": "1.0"
    }
}

Physics properties (gravity and drag along X, Y and Z) are optional and default to 0.

How do I update and render the game world in my main loop

In your game loop (or in your SDL_AppIterate method), lock the game state, call the game update function, and then unlock the game state

PASS(e, akgl_game_state_lock());
PASS(e, akgl_renderer->frame_start(akgl_renderer));
SDL_RenderClear(akgl_renderer->sdl_renderer);
PASS(e, akgl_game_update(NULL));
PASS(e, akgl_renderer->frame_end(akgl_renderer));
PASS(e, akgl_game_state_unlock());

How do I get an actor on screen

Load a sprite for a character. Sprites are JSON documents describing 2D sprites, frames, and looping. Sprites are named, and sprite names must be unique.

PASS(e, akgl_sprite_load_json(SOME_FILENAME))

Load a character from a JSON file. Characters map sprites to actor states and define physics characteristics like movement speed. Each character is named, and character names must be unique.

PASS(e, akgl_character_load_json(SOME_FILENAME))

You don't strictly have to load sprites and characters from json files, you can initialize them yourself, it's just tedious work. Here's an example of initializing a 32x32 sprite from a spritesheet that uses the first 4 frames in a looping animation.

akgl_SpriteSheet *sheet;
akgl_Sprite *sprite;
akgl_Character *character;
PASS(e, akgl_heap_next_spritesheet(&sheet);
PASS(e, akgl_spritesheet_initialize(sheet, 32, 32, IMAGE_FILENAME));
PASS(e, akgl_heap_next_sprite(&sprite));
PASS(e, akgl_sprite_initialize(sprite, SPRITE_NAME, &sheet);
sprite->frames = 4;
sprite->frameids = [0, 1, 2, 3];
sprite->width = 32;
sprite->height = 32;
sprite->speed = 1000;
sprite->loop = true;
strncpy((char *)&sprite->name, "SPRITE NAME", AKGL_SPRITE_MAX_NAME_LENGTH);
PASS(e, akgl_heap_next_character(&character));
PASS(e, akgl_character_initialize(&character, "CHAR NAME"));
PASS(e, akgl_character_sprite_add(&character, &sprite, STATE_MASK));
// Set the character acceleration and scale if desired
character->ax = 64.0;
character->ay = 64.0;
character->sx = 2.0;
character->sy = 2.0;

Initialize an actor. Actors are named ("player", "Quest NPC", whatever) and names must be unique.

akgl_Actor *myactor = NULL;
PASS(e, akgl_heap_next_actor(&myactor);
PASS(e, akgl_actor_initialize(&myactor, "ACTOR_NAME"));

Assign a character to the actor by looking up the akgl_Character from the AKGL registry and assign it.

myactor->basechar = SDL_GetPointerProperty(
    AKGL_REGISTRY_CHARACTER,
	"CHARACTER_NAME",
	NULL);
FAIL_ZERO_BREAK(e, myactor->basechar, AKERR_REGISTRY, "Character missing");

Give the actor a position and a state, and turn it visible.

myactor->state = 9AKGL_ACTOR_STATE_ALIVE | AKGL_ACTOR_STATE_FACE_LEFT);
myactor->x = 320;
myactor->y = 240;
myactor->visible = true;

What are in Sprite and Character files

Sprite files:

{
    "spritesheet": {
    	"filename": "RELATIVE_IMAGE_FILE_REFERENCE",
	    "frame_width": int,
	    "frame_height": int
    },
    "name": "UNIQUE_SPRITE_NAME",
    "width": int,
    "height": int,
    "speed": int,
    "loop": boolean,
    "loopReverse": boolean,
    "frames": [
	    int
    ]
}

• frames references the frame indexes in the spritesheet that should be used for this animation. Spritesheets are counted from the top left corner going to the right according to the spritesheet frame_width and frame_height.
• loop says whether or not we should loop the animation
• loopReverse says whether or not we should "bounce" the animation (when we reach the end of the frames, start counting back to the beginning, then count to the end, etc). Otherwise the frames are displayed from 0..n and then cycles back to 0.
• speed is the number of milliseconds each frame in the animation should appear on the screen

Character files:

{
    "name": "UNIQUE_CHARACTER_NAME",
    "speedtime": 8,
    "speed_x": 0,
    "speed_y": 0,
    "acceleration_x": 0,
    "acceleration_y": 0,
    "sprite_mappings": [
		{
			"state": [
				"AKGL_ACTOR_STATE_ALIVE",
				"AKGL_ACTOR_STATE_FACE_UP",
				"AKGL_ACTOR_STATE_MOVING_UP"		
			],		
			"sprite": "menupointer"
		}[, ...]
    ]
}

• speedtime appears to be legacy and unused.
• speed_[xy] and acceleration_[xy] are physics parameters that specify the top speed and acceleration rate (in pixels per nanosecond) of the character in physics simulations. The effect of acceleration depends on the physics simulation being used at the time (which may or may not account for gravity, drag, etc).
• sprite_mappings map a set of actor state flag bitmasks (assume everything in state is ORed together) to a sprite name. The game engine uses this to automatically pick the correct sprite (by name) for a given set of state flags. You need one of these for every possible state the character may be used in.

How do I load a tilemap from the filesystem and display it on screen with my actors

The engine ONLY supports TilED TMJ tilemaps with tileset external references. Load a tilemap into the global akgl_Tilemap *gamemap object.

PASS(e, akgl_tilemap_load(PATHSTRING, akgl_gamemap));

Actors will be automatically populated from objects in the tilemap object layers. Actor state flags here must be expressed as an integer, you can't (yet) use the same array of strings that is used in character json files.

         "objects":[
                {
                 "gid":147,
                 "height":16,
                 "id":1,
                 "name":"player",
                 "properties":[
                        {
                         "name":"character",
                         "type":"string",
                         "value":"little guy"
                        }, 
                        {
                         "name":"state",
                         "type":"int",
                         "value":24
                        }],
                 "rotation":0,
                 "type":"actor",
                 "visible":true,
                 "width":16,
                 "x":440.510088317656,
                 "y":140.347239175702
                }[, ... ] 

Check if the tilemap wants to use its own physics, and if you want to allow that, override the global physics simulation

if ( akgl_gamemap->use_own_physics == true ) {
	akgl_physics = &akgl_gamemap->physics;
}

Tilemap physics specification follows. A map can specify its own physics properties (drag, gravity) without specifying a custom model.

 "properties":[
        {
         "name":"physics.drag.y",
         "type":"float",
         "value":0
        }, 
        {
         "name":"physics.gravity.y",
         "type":"float",
         "value":0
        }, 
        {
         "name":"physics.model",
         "type":"string",
         "value":"arcade"
        }],

The global akgl_gamemap object is automatically displayed if it is populated. Actors are drawn at the appropriate map layer depending on the actor's layer property (warning: this may be replaced with a z property soon.)

How do I get the screen width and height

The most direct is to call SDL_GetCurrentDisplayMode to get the parameters from the returned SDL_DisplayMode structure (->w and ->h).

The simplest way is to check the global akgl_camera object's akgl_camera->w and akgl_camera->h object. You may have more than one camera on a scene, and it's theoretically possible that the global camera object has been overriden and no longer represents the full screen.

The most reliable engine-centric way is to use akgl_get_property to get the property from the engine. Properties are read and stored as strings, so if you need to do these kinds of things a lot, cache the integer value somewhere.

akgl_String *width = NULL;
int screenwidth = NULL;
PASS(e, akgl_get_property("game.screenwidth", &width, "0"));
PASS(e, aksl_atoi(width->data, &screenwidth));
PASS(e, akgl_heap_release_string(width));

Git hooks

The repository ships a pre-commit hook that keeps committed C sources in the project's canonical format (Emacs cc-mode "stroustrup"; see AGENTS.md for the full style guide). The hook lives in scripts/hooks/ and is version controlled, but Git configuration is not cloned, so every clone has to be pointed at it once:

git config core.hooksPath scripts/hooks

Confirm it took effect:

git rev-parse --git-path hooks     # should print: scripts/hooks

That is the whole installation. The hook is already committed with its executable bit set, so nothing needs chmod.

What the hook does

On each commit it looks at the staged content of any added, copied, modified, or renamed .c/.h file under src/, include/, tests/, or util/, and reindents it if it does not already match the canonical style. Checking the staged content rather than the working tree means what lands in the commit is what was actually verified.

When a file needs reindenting, the hook fixes it in the working tree and re-stages it — but only when the index and working tree agree for that file. If they differ, you have staged part of a file with git add -p, and re-staging would sweep your unstaged work into the commit. Rather than do that silently the hook stops and prints the commands to run yourself:

scripts/reindent.sh path/to/file.c
git add path/to/file.c

include/akgl/SDL_GameControllerDB.h is generated and always skipped.

Requirements

The hook drives Emacs in batch mode, because cc-mode's indentation engine is the definition of the style and clang-format cannot reproduce it exactly. If emacs is not on PATH the hook prints a warning and allows the commit — a hook that refuses to run without an optional tool only teaches people to reach for --no-verify. Install Emacs to get the check; without it, formatting is on you.

Bypassing and uninstalling

Skip the hook for a single commit:

git commit --no-verify

Remove it entirely:

git config --unset core.hooksPath

If you already have local hooks

core.hooksPath replaces the hooks directory outright — once it is set, Git stops reading .git/hooks/ altogether, so any hooks you keep there will silently stop firing. If that matters, leave core.hooksPath unset and symlink just this one hook instead:

ln -s ../../scripts/hooks/pre-commit .git/hooks/pre-commit

Formatting without the hook

The hook is a convenience, not the source of truth. The same check is available directly, and is what you would run in CI:

scripts/reindent.sh --check     # list non-conforming files; exit 1 if any
scripts/reindent.sh             # reindent every tracked C source in place
scripts/reindent.sh src/game.c  # reindent specific files

--check exits 0 when everything conforms, 1 when a file needs reindenting, and 2 if Emacs is missing or the script cannot run — so a CI job that treats any non-zero status as failure will not mistake a broken toolchain for a clean tree.

Mutation testing

The mutation harness makes one deliberate source-code change at a time in a scratch copy, then rebuilds and runs the passing CTest suite to measure whether tests detect the change. The known-failing character test is excluded by default.

cmake --build build --target mutation
scripts/mutation_test.py --target src/tilemap.c --list
scripts/mutation_test.py --target src/tilemap.c --max-mutants 10
scripts/mutation_test.py --threshold 40 --junit mutation-junit.xml

The default run covers all libakgl-owned files under src/. Use repeated --target options to narrow the scope. A surviving mutant identifies behavior that the current tests do not verify; the script prints its file, line, operator, and exact edit. The real working tree is never mutated.

Performance testing

tests/perf.c and tests/perf_render.c are benchmarks rather than unit tests: they drive the hot paths — pool acquire and release, the registry, the physics sweep, the per-actor update and render, the tilemap draw, text, and asset loading — and print what each one costs per operation.

ctest --test-dir build -L perf --output-on-failure   # benchmarks only, about 30 seconds
ctest --test-dir build -LE perf                      # everything except the benchmarks
AKGL_BENCH_SCALE=0.1 ctest --test-dir build -L perf  # a tenth of the iterations

Each measurement is the best of five runs and is held to a budget set at roughly ten times the recorded baseline, so a suite that turns red means an algorithmic regression rather than a busy machine. Budgets are enforced only in an optimized build at full scale; below AKGL_BENCH_SCALE=1.0, and in a coverage build, they are reported without failing.

PERFORMANCE.md carries the recorded baseline, the frame budget it adds up to, and what the numbers say — including the raw-SDL control rows that separate what libakgl costs from what the rasterizer costs. The six defects the stress tests turned up, and the targets the numbers are measured against, are in TODO.md under Performance.

Memory checking

memcheck runs the suites that already exist under valgrind rather than adding suites of its own. The perf binaries carry most of it: they are the only programs in the tree that load assets, draw a scene, and run a frame loop in one process, and tests/benchutil.h cuts their iteration counts by three orders of magnitude when it detects valgrind — a benchmark walks one path a hundred thousand times, a leak check wants every path walked once.

cmake --build build --target memcheck   # everything, about 30 seconds
scripts/memcheck.sh -R tilemap          # one suite; ctest selection flags pass through
scripts/memcheck.sh -LE perf            # skip the benchmarks

The run forces SDL_VIDEO_DRIVER=dummy, SDL_RENDER_DRIVER=software and SDL_AUDIO_DRIVER=dummy so the vendor GPU stack is never loaded — that removes thousands of unfixable findings inside the driver without suppressing anything. Definite leaks, invalid accesses and uninitialised reads are counted and set the exit status; "still reachable" is not, because that is what SDL and FreeType keep for the process lifetime. Suppressions for genuine third-party findings are in scripts/valgrind.supp.

What it found the first time it ran is in TODO.md under Memory checking.