add animations (lerp only for now)

include/dangerzone/render/anim.h

@@ -1,22 +1,55 @@
-#pragma once
+#ifndef DANGERZONE_RENDER_ANIM_H
+#define DANGERZONE_RENDER_ANIM_H
 
-#include <dangerzone/engine.h>
+#include <stdbool.h>
+#include <stddef.h>
 #include <stdint.h>
 
-/**
- * animate a rectangle's position changing over time
- * => x0 -> x1, y0 -> y1, all else stays the same
- *
- * ONLY DOES ONE FRAME OF THE ANIMATION
+#define ANIM_MAX_TRACKS 64
+
+typedef struct {
+    float x;
+    float y;
+    float w;
+    float h;
+} anim_rect_t;
+
+/* payload is application data; the animation module does not interpret it. */
+typedef struct {
+    uint32_t payload;
+    anim_rect_t from;
+    anim_rect_t to;
+} anim_track_t;
+
+typedef struct {
+    uint32_t payload;
+    anim_rect_t rect;
+} anim_item_t;
+
+typedef struct {
+    anim_track_t tracks[ANIM_MAX_TRACKS];
+    anim_item_t items[ANIM_MAX_TRACKS];
+    size_t count;
+    float elapsed;
+    float duration;
+    bool active;
+} anim_t;
+
+void anim_init(anim_t *anim);
+
+/*
+ * Start tracks from their initial rectangles to their destination rectangles.
+ * Returns false for invalid input or if count exceeds ANIM_MAX_TRACKS.
+ * A zero-duration animation completes immediately.
  */
-void
-anim_rect_pos(
-    framebuffer_e framebuffer,
-    uint32_t x0,
-    uint32_t y0,
-    uint32_t x1,
-    uint32_t y1,
-    uint32_t w,
-    uint32_t h,
-    uint32_t color
-);
+bool anim_start(anim_t *anim, const anim_track_t *tracks,
+                size_t count, float duration);
+
+/* Advance by nonnegative seconds. Returns true once the animation is finished. */
+bool anim_update(anim_t *anim, float dt);
+
+bool anim_is_active(const anim_t *anim);
+size_t anim_count(const anim_t *anim);
+const anim_item_t *anim_items(const anim_t *anim);
+
+#endif