Finish animation update loop with loop/pingpong/reverse/stop flags, clean up keyframe sampling, add coverage

- animationUpdate now advances and resolves boundary crossings for
  ANIMATION_FLAG_LOOP, ANIMATION_FLAG_PINGPONG, ANIMATION_FLAG_REVERSE, and
  the STOP_BEGINNING/STOP_END flags, firing onLoop/onComplete appropriately;
  guards against LOOP+PINGPONG being set together and moves the
  duration-must-be-positive check into animationInit
- keyframeGetValue clamps to the last keyframe's value instead of dividing
  by zero once time reaches it, and its keyframe walk drops a branch that's
  unreachable after that clamp
- Adds test/animation/test_animation.c covering init, per-layer sampling,
  and the full animationUpdate flag matrix

src/dusk/animation/animation.c

@@ -11,42 +11,115 @@
 void animationInit(
   animation_t *anim,
   keyframe_t *keyframes,
-  uint16_t keyframeCount
+  uint16_t *keyframeCounts,
+  const uint16_t layerCount
 ) {
   assertNotNull(anim, "Animation pointer cannot be null.");
   assertNotNull(keyframes, "Keyframes pointer cannot be null.");
-  assertTrue(keyframeCount > 0, "Keyframe count must be more than 0.");
+  assertNotNull(keyframeCounts, "Keyframe counts pointer cannot be null.");
+  assertTrue(layerCount > 0, "Layer count must be greater than zero.");
 
+  memoryZero(anim, sizeof(animation_t));
   anim->keyframes = keyframes;
-  anim->keyframeCount = keyframeCount;
+  anim->keyframeCounts = keyframeCounts;
+  anim->layerCount = layerCount;
+
+  // Determine duration
+  float_t duration = 0.0f;
+  for(uint16_t layer = 0; layer < layerCount; layer++) {
+    uint16_t keyframeCount = keyframeCounts[layer];
+    assertTrue(keyframeCount > 0, "Keyframe count invalid.");
+    keyframe_t *layerKeyframes = keyframes + layer * keyframeCount;
+
+    #ifdef DUSK_ASSERTIONS
+      // Check that the keyframes are sorted by time.
+      for(uint16_t i = 1; i < keyframeCount; i++) {
+        assertTrue(
+          layerKeyframes[i].time >= layerKeyframes[i - 1].time,
+          "Keyframes must be sorted by time."
+        );
+      }
+    #endif
+
+    keyframe_t *lastKeyframe = layerKeyframes + keyframeCount - 1;
+    duration = mathMax(duration, lastKeyframe->time);
+  }
+  assertTrue(duration > 0, "Animation duration must be greater than 0.");
+  anim->duration = duration;
 }
 
-float_t animationGetValue(animation_t *anim, const float_t time) {
+float_t animationGetLayerValue(const animation_t *anim, const uint16_t layer) {
   assertNotNull(anim, "Animation pointer cannot be null.");
-  assertNotNull(anim->keyframes, "Keyframes pointer cannot be null.");
-  assertTrue(anim->keyframeCount > 0, "Keyframe count invalid.");
-  assertTrue(time >= 0, "Time must be non-negative.");
-  
-  keyframe_t *start;
-  keyframe_t *end;
-  keyframe_t *last = anim->keyframes + anim->keyframeCount - 1;
-  keyframe_t *current = anim->keyframes;
-  start = current;
+  assertTrue(layer < anim->layerCount, "Layer index out of bounds.");
 
-  do {
-    if(current->time > time) {
-      end = current;
-      break;
+  uint16_t keyframeCount = anim->keyframeCounts[layer];
+  keyframe_t *layerKeyframes = anim->keyframes + layer * keyframeCount;
+  return keyframeGetValue(layerKeyframes, keyframeCount, anim->time);
+}
+
+void animationUpdate(
+  animation_t *anim,
+  const float_t deltaTime
+) {
+  assertNotNull(anim, "Animation pointer cannot be null.");
+  assertTrue(deltaTime >= 0, "Delta time must be non-negative.");
+
+  bool_t justCompleted = false;
+
+  if(!(anim->flags & ANIMATION_FLAG_INTERNAL_COMPLETED)) {
+    bool_t loop = (anim->flags & ANIMATION_FLAG_LOOP) != 0;
+    bool_t pingpong = (anim->flags & ANIMATION_FLAG_PINGPONG) != 0;
+    assertFalse(
+      loop && pingpong,
+      "Cannot set both ANIMATION_FLAG_LOOP and ANIMATION_FLAG_PINGPONG."
+    );
+    bool_t backward = pingpong
+      ? (anim->flags & ANIMATION_FLAG_INTERNAL_PINGPONG_BACKWARD) != 0
+      : (anim->flags & ANIMATION_FLAG_REVERSE) != 0;
+
+    // Resolve boundary crossings one at a time, so a single large deltaTime
+    // can correctly loop/pingpong across multiple boundaries in one call.
+    float_t remaining = deltaTime;
+    while(remaining > 0.0f) {
+      float_t toBoundary = (
+        backward ? anim->time : (anim->duration - anim->time)
+      );
+      if(remaining < toBoundary) {
+        anim->time += backward ? -remaining : remaining;
+        break;
+      }
+
+      remaining -= toBoundary;
+      anim->time = backward ? 0.0f : anim->duration;
+
+      bool_t stopHere = backward
+        ? (anim->flags & ANIMATION_FLAG_STOP_BEGINNING) != 0
+        : (anim->flags & ANIMATION_FLAG_STOP_END) != 0;
+
+      if(stopHere) {
+        justCompleted = true;
+        break;
+      } else if(pingpong) {
+        backward = !backward;
+        if(backward) anim->flags |= ANIMATION_FLAG_INTERNAL_PINGPONG_BACKWARD;
+        else anim->flags &= ~ANIMATION_FLAG_INTERNAL_PINGPONG_BACKWARD;
+      } else if(loop) {
+        anim->time = backward ? anim->duration : 0.0f;
+        if(anim->onLoop) anim->onLoop(anim->user);
+      } else {
+        justCompleted = true;
+        break;
+      }
     }
-    start = current;
-    current++;
 
-    if(current > last) {
-      end = start;
-      break;
-    }
-  } while(true);
+    if(justCompleted) anim->flags |= ANIMATION_FLAG_INTERNAL_COMPLETED;
+  }
 
-  float_t t = (time - start->time) / (end->time - start->time);
-  return mathLerp(start->value, end->value, easingApply(start->easing, t));
+  // Call onUpdate for each layer.
+  for(uint16_t layer = 0; layer < anim->layerCount; layer++) {
+    float_t value = animationGetLayerValue(anim, layer);
+    if(anim->onUpdate) anim->onUpdate(layer, value, anim->user);
+  }
+
+  if(justCompleted && anim->onComplete) anim->onComplete(anim->user);
 }

src/dusk/animation/animation.h

@@ -6,29 +6,89 @@
 #pragma once
 #include "keyframe.h"
 
+#define ANIMATION_FLAG_LOOP (1 << 0)
+#define ANIMATION_FLAG_REVERSE (1 << 1)
+#define ANIMATION_FLAG_PINGPONG (1 << 2)
+#define ANIMATION_FLAG_STOP_BEGINNING (1 << 3)
+#define ANIMATION_FLAG_STOP_END (1 << 4)
+
+// Internal - tracks which direction a pingponging animation is currently
+// travelling. Do not set this manually, it is managed by animationUpdate().
+#define ANIMATION_FLAG_INTERNAL_PINGPONG_BACKWARD (1 << 7)
+
+// Internal - set once the animation has stopped advancing (see
+// animationUpdate()). Do not set this manually. There is currently no way to
+// restart a completed animation short of clearing this bit and resetting
+// anim->time by hand.
+#define ANIMATION_FLAG_INTERNAL_COMPLETED (1 << 6)
+
 typedef struct {
   keyframe_t *keyframes;
-  uint16_t keyframeCount;
+  uint16_t *keyframeCounts;
+  uint16_t layerCount;
+  float_t time;
+  float_t duration;
+  uint8_t flags;
+
+  void *user;
+  void (*onUpdate)(const uint16_t layer, const float_t value, void *user);
+  void (*onComplete)(void *user);
+  void (*onLoop)(void *user);
 } animation_t;
 
 /**
- * Initializes an animation.
- * 
- * @param anim The animation to initialize.
- * @param keyframes The keyframes to use for the animation.
- * @param keyframeCount The number of keyframes in the animation.
+ * Initializes an animation with the given keyframes and layer count.
+ *
+ * @param anim Pointer to the animation to initialize.
+ * @param keyframes Pointer to the array of keyframes for each layer.
+ * @param keyframeCount Number of keyframes in each layer.
+ * @param layerCount Number of layers in the animation.
  */
 void animationInit(
   animation_t *anim,
   keyframe_t *keyframes,
-  uint16_t keyframeCount
+  uint16_t *keyframeCounts,
+  const uint16_t layerCount
 );
 
 /**
- * Gets the value of the animation at a given time.
+ * Sets the current time of the animation, clamping it to the valid range.
+ * This will call the onUpdate callback but none of the other callbacks.
  * 
- * @param anim The animation to get the value from.
- * @param time The time at which to get the value, in seconds.
- * @return The value of the animation at the given time.
+ * @param anim Pointer to the animation to set the time for.
+ * @param time The new time to set for the animation.
  */
-float_t animationGetValue(animation_t *anim, const float_t time);
+void animationSetTime(animation_t *anim, const float_t time);
+
+/**
+ * Gets the current value of a specific layer in the animation based on the
+ * current animation time.
+ */
+float_t animationGetLayerValue(const animation_t *anim, const uint16_t layer);
+
+/**
+ * Updates the animation state based on the elapsed time. Advances anim->time
+ * by deltaTime (or against it, if ANIMATION_FLAG_REVERSE is set), then
+ * resolves whatever happens when it reaches the 0 or duration boundary:
+ *
+ * - ANIMATION_FLAG_PINGPONG: reflects off the boundary and continues playing
+ *   in the opposite direction, forever, unless stopped (see below).
+ * - ANIMATION_FLAG_LOOP: wraps back around to the other boundary and keeps
+ *   playing in the same direction, forever, unless stopped (see below).
+ * - ANIMATION_FLAG_STOP_BEGINNING / ANIMATION_FLAG_STOP_END: when the
+ *   animation reaches that specific boundary, it clamps there and stops
+ *   (firing onComplete) instead of looping/pingponging past it.
+ * - If none of the above apply at a boundary, the animation clamps there and
+ *   stops, firing onComplete.
+ *
+ * onUpdate is called for every layer on every call. onLoop is called each
+ * time a loop wraps around. onComplete is called at most once, the moment
+ * the animation stops advancing.
+ *
+ * @param anim Pointer to the animation to update.
+ * @param deltaTime Time elapsed since the last update (in seconds).
+ */
+void animationUpdate(
+  animation_t *anim,
+  const float_t deltaTime
+);

src/dusk/animation/keyframe.c

@@ -27,27 +27,18 @@ float_t keyframeGetValue(
     }
   #endif
 
-  keyframe_t *start;
-  keyframe_t *end;
   keyframe_t *last = (keyframe_t *)(keyframes + keyframeCount - 1);
   if(time >= last->time) return last->value;
 
+  // Since time < last->time (checked above), current is guaranteed to stop
+  // at or before reaching last, so no separate end-of-array check is needed.
   keyframe_t *current = (keyframe_t *)keyframes;
-  start = current;
-
-  do {
-    if(current->time > time) {
-      end = current;
-      break;
-    }
+  keyframe_t *start = current;
+  while(current->time <= time) {
     start = current;
     current++;
-
-    if(current > last) {
-      end = start;
-      break;
-    }
-  } while(true);
+  }
+  keyframe_t *end = current;
 
   float_t t = (time - start->time) / (end->time - start->time);
   return mathLerp(start->value, end->value, easingApply(start->easing, t));