+ sub-image.
+
+ Computing all the preceding images is too slow, so we maintain a
+ cache of previously computed images. We have to maintain a cache
+ separate from the image cache, because the images may be scaled
+ before display. */
+
+struct animation_cache
+{
+ MagickWand *wand;
+ int index;
+ struct timespec update_time;
+ struct animation_cache *next;
+ char signature[FLEXIBLE_ARRAY_MEMBER];
+};
+
+static struct animation_cache *animation_cache = NULL;
+
+static struct animation_cache *
+imagemagick_create_cache (char *signature)
+{
+ struct animation_cache *cache
+ = xmalloc (offsetof (struct animation_cache, signature)
+ + strlen (signature) + 1);
+ cache->wand = 0;
+ cache->index = 0;
+ cache->next = 0;
+ strcpy (cache->signature, signature);
+ return cache;
+}
+
+/* Discard cached images that haven't been used for a minute. */
+static void
+imagemagick_prune_animation_cache (void)
+{
+ struct animation_cache **pcache = &animation_cache;
+ struct timespec old = timespec_sub (current_timespec (),
+ make_timespec (60, 0));
+
+ while (*pcache)
+ {
+ struct animation_cache *cache = *pcache;
+ if (timespec_cmp (old, cache->update_time) <= 0)
+ pcache = &cache->next;
+ else
+ {
+ if (cache->wand)
+ DestroyMagickWand (cache->wand);
+ *pcache = cache->next;
+ xfree (cache);
+ }
+ }
+}