Too hungry to think. What would Goku do?

include/hexagram/anim.h

@@ -34,7 +34,7 @@ typedef struct _hexagram_anim_action {
 typedef struct _hexagram_anim_stop {
     hexagram_anim_action *actions;
     size_t actionc;
-    double duration_s;
+    double duration;
 } hexagram_anim_stop;
 
 typedef struct _hexagram_anim {

src/anim.c

@@ -1,4 +1,5 @@
 #include <stdlib.h>
+#include <string.h>
 
 #include <hexagram/anim.h>
 
@@ -8,6 +9,43 @@ void hexagram_anim_init(hexagram_anim *anim) {
     gettimeofday(&anim->start, NULL);
 }
 
-int hexagram_anim_step(hexagram_anim *anim, cairo_t *bg, cairo_t *fg) {
-
+static inline double tv_seconds(struct timeval *tv) {
+    return (double)tv->tv_sec + (double)tv->tv_usec / 1000000.0;
+}
+
+static inline double stop_offset(hexagram_anim *anim, size_t index) {
+    double offset = 0.0;
+    size_t i;
+
+    for (i=0; i<index; i++) {
+        offset += anim->stops[i].duration;
+    }
+
+    return offset;
+}
+
+static inline size_t stop_index(hexagram_anim *anim, double offset) {
+    return 0;
+}
+
+int hexagram_anim_step(hexagram_anim *anim, cairo_t *bg, cairo_t *fg) {
+    struct timeval tv;
+    double offset, interval;
+    size_t i;
+
+    if (anim->current >= anim->count) {
+        goto done;
+    }
+
+    gettimeofday(&anim->now, NULL);
+
+    timersub(&anim->now, &anim->start, &tv);
+
+    interval = tv_seconds(&tv);
+
+done:
+    return 0;
+
+next:
+    return 1;
 }