Docs

2026-06-18 14:59:21 -05:00
parent 6135d60ddc
commit 730a5b2b10
17 changed files with 2825 additions and 415 deletions
@@ -0,0 +1,74 @@
+# Animation System
+
+Source: `src/dusk/animation/`
+
+Lightweight keyframe-based value interpolation using fixed-point math throughout.
+
+---
+
+## Easing (`animation/easing.h`)
+
+`easingApply(type, t)` applies an easing function to a normalized time value `t ∈ [0, FIXED_ONE]` and returns the eased value in the same range.
+
+All functions are also callable directly:
+
+```c
+fixed_t t = FIXED(0.5f);
+fixed_t out = easingApply(EASING_IN_OUT_CUBIC, t);
+```
+
+Available easing types (all in `easingtype_t`):
+
+| Enum value | Curve |
+|---|---|
+| `EASING_LINEAR` | straight line |
+| `EASING_IN_SINE` / `OUT` / `IN_OUT` | sinusoidal |
+| `EASING_IN_QUAD` / `OUT` / `IN_OUT` | quadratic |
+| `EASING_IN_CUBIC` / `OUT` / `IN_OUT` | cubic |
+| `EASING_IN_QUART` / `OUT` / `IN_OUT` | quartic |
+| `EASING_IN_BACK` / `OUT` / `IN_OUT` | overshoots slightly |
+
+`EASING_FUNCTIONS[EASING_COUNT]` is a table of `easingfn_t` function pointers for when you need to pick an easing at runtime without a switch.
+
+---
+
+## Keyframes (`animation/keyframe.h`)
+
+```c
+typedef struct {
+  fixed_t time;          // time point this keyframe is at
+  fixed_t value;         // output value at this time
+  easingtype_t easing;   // easing to apply when interpolating toward the NEXT keyframe
+} keyframe_t;
+```
+
+Keyframe arrays should be sorted ascending by `time`.
+
+---
+
+## Animation (`animation/animation.h`)
+
+`animation_t` wraps a keyframe array and provides value lookup:
+
+```c
+keyframe_t frames[] = {
+  { FIXED(0.0f), FIXED(0.0f), EASING_LINEAR },
+  { FIXED(1.0f), FIXED(1.0f), EASING_IN_OUT_CUBIC },
+  { FIXED(2.0f), FIXED(0.0f), EASING_LINEAR },
+};
+
+animation_t anim;
+animationInit(&anim, frames, 3);
+
+fixed_t value = animationGetValue(&anim, FIXED(0.75f));   // interpolated
+```
+
+`animationGetValue` finds the surrounding keyframes for the given `time`, computes the local `t` within that segment, applies the keyframe's easing, and linearly interpolates between the two keyframe values.
+
+The animation does not own the keyframe array — it holds a pointer. Pass a static or long-lived array.
+
+---
+
+## Usage in the engine
+
+Entity animations (`entityanim_t`) do NOT use this system — they use a simple countdown timer (`animTime`) and a state enum. The `animation_t` system is intended for property animation: UI transitions, camera easing, visual effects, anything that needs a time → value curve.