libakgl/README.md

## How do I initialize a game

Initialize the global game object with info about your game

```c
	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

```c
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. 

```c
PASS(e, akgl_registry_load_properties(YOUR_REGISTR_FILEPATH));
```

Initialize your physics engine and renderer of choice

```c
PASS(e, akgl_render_init2d(renderer));
PASS(e, akgl_physics_init_arcade(physics));
```

Unlock the game state

```c
PASS(e, akgl_game_state_unlock());
```

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

```json
{
    "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

```c
PASS(e, akgl_game_state_lock());
PASS(e, renderer->frame_start(renderer));
SDL_RenderClear(renderer->sdl_renderer);
PASS(e, akgl_game_update(NULL));
PASS(e, renderer->frame_end(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.

```c
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.

```c
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.

```c
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.

```c
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.

```c
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.

```c
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:

```json
{
    "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:

```c
{
    "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 `OR`ed 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.

```c
PASS(e, akgl_tilemap_load(PATHSTRING, 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.

```json
         "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

```c
if ( gamemap->use_own_physics == true ) {
	physics = &gamemap->physics;
}
```

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

```json
 "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 `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 `camera` object's `camera->w` and `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.

```c
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:

```sh
git config core.hooksPath scripts/hooks
```

Confirm it took effect:

```sh
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:

```sh
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:

```sh
git commit --no-verify
```

Remove it entirely:

```sh
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:

```sh
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:

```sh
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.

```sh
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.

```sh
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, and the six defects the stress tests turned up.