From 64f825465de9fa30c4dfe2707067efdb96110db8 Mon Sep 17 00:00:00 2001
From: Elizabeth Hunt <me@liz.coffee>
Date: Thu, 23 Oct 2025 21:59:37 -0700
Subject: Init

---
 .../coffee/liz/ecs/animation/AnimationSystem.kt    | 77 ++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 composeApp/src/commonMain/kotlin/coffee/liz/ecs/animation/AnimationSystem.kt

(limited to 'composeApp/src/commonMain/kotlin/coffee/liz/ecs/animation/AnimationSystem.kt')

diff --git a/composeApp/src/commonMain/kotlin/coffee/liz/ecs/animation/AnimationSystem.kt b/composeApp/src/commonMain/kotlin/coffee/liz/ecs/animation/AnimationSystem.kt
new file mode 100644
index 0000000..7ae405e
--- /dev/null
+++ b/composeApp/src/commonMain/kotlin/coffee/liz/ecs/animation/AnimationSystem.kt
@@ -0,0 +1,77 @@
+package coffee.liz.ecs.animation
+
+import coffee.liz.ecs.System
+import coffee.liz.ecs.World
+
+/**
+ * System that updates animation playback state for all entities with an Animator component.
+ *
+ * This system:
+ * - Updates elapsed time for playing animations
+ * - Advances frame indices based on frame duration
+ * - Handles loop modes (ONCE, LOOP, PING_PONG)
+ * - Stops animations when they complete (for ONCE mode)
+ */
+class AnimationSystem : System {
+    override fun update(world: World, deltaTime: Float) {
+        // Query all entities that have both Animator and SpriteSheet
+        world.query(Animator::class, SpriteSheet::class).forEach { entity ->
+            val animator = entity.get(Animator::class) ?: return@forEach
+
+            // Skip if animation is not playing
+            if (!animator.playing) return@forEach
+
+            // Get the current animation clip
+            val clip = animator.clips[animator.currentClip] ?: return@forEach
+
+            // Accumulate elapsed time
+            animator.elapsed += deltaTime
+
+            // Advance frames while we have enough elapsed time
+            while (animator.elapsed >= clip.frameDuration) {
+                animator.elapsed -= clip.frameDuration
+                advanceFrame(animator, clip)
+            }
+        }
+    }
+
+    /**
+     * Advances the animation to the next frame based on loop mode.
+     */
+    private fun advanceFrame(animator: Animator, clip: AnimationClip) {
+        animator.frameIndex += animator.direction
+
+        when (clip.loopMode) {
+            LoopMode.ONCE -> {
+                // Play once and stop on last frame
+                if (animator.frameIndex >= clip.frameNames.size) {
+                    animator.frameIndex = clip.frameNames.size - 1
+                    animator.playing = false
+                }
+            }
+
+            LoopMode.LOOP -> {
+                // Loop back to beginning
+                if (animator.frameIndex >= clip.frameNames.size) {
+                    animator.frameIndex = 0
+                } else if (animator.frameIndex < 0) {
+                    // Handle negative wrap (shouldn't happen in LOOP but be safe)
+                    animator.frameIndex = clip.frameNames.size - 1
+                }
+            }
+
+            LoopMode.PING_PONG -> {
+                // Bounce back and forth
+                if (animator.frameIndex >= clip.frameNames.size) {
+                    // Hit the end, reverse direction
+                    animator.frameIndex = (clip.frameNames.size - 2).coerceAtLeast(0)
+                    animator.direction = -1
+                } else if (animator.frameIndex < 0) {
+                    // Hit the beginning, reverse direction
+                    animator.frameIndex = 1.coerceAtMost(clip.frameNames.size - 1)
+                    animator.direction = 1
+                }
+            }
+        }
+    }
+}
-- 
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