fix animated gif playback

A casualty of b8dcfba was that
the decoded gif would get reset each time the texture filled up.

Take care to move that cached into the newly minted glyphcache.

wezterm-gui/src/glyphcache.rs

@@ -218,19 +218,19 @@ impl BlockKey {
 }
 
 #[derive(Debug)]
-struct ImageFrame {
+pub struct ImageFrame {
     duration: Duration,
     image: ::window::bitmaps::Image,
 }
 
 #[derive(Debug)]
-enum CachedImage {
+pub enum CachedImage {
     Animation(DecodedImage),
     SingleFrame,
 }
 
 #[derive(Debug)]
-struct DecodedImage {
+pub struct DecodedImage {
     frame_start: Instant,
     current_frame: usize,
     frames: Vec<ImageFrame>,
@@ -318,7 +318,7 @@ pub struct GlyphCache<T: Texture2d> {
     glyph_cache: HashMap<GlyphKey, Rc<CachedGlyph<T>>>,
     pub atlas: Atlas<T>,
     fonts: Rc<FontConfiguration>,
-    image_cache: LruCache<usize, CachedImage>,
+    pub image_cache: LruCache<usize, CachedImage>,
     frame_cache: HashMap<(usize, usize), Sprite<T>>,
     line_glyphs: HashMap<LineKey, Sprite<T>>,
     block_glyphs: HashMap<BlockKey, Sprite<T>>,

wezterm-gui/src/renderstate.rs

@@ -348,9 +348,19 @@ impl RenderState {
         size: Option<usize>,
     ) -> anyhow::Result<()> {
         let size = size.unwrap_or_else(|| self.glyph_cache.borrow().atlas.size());
-        let mut glyph_cache = GlyphCache::new_gl(&self.context, fonts, size, metrics)?;
-        self.util_sprites = UtilSprites::new(&mut glyph_cache, metrics)?;
-        *self.glyph_cache.borrow_mut() = glyph_cache;
+        let mut new_glyph_cache = GlyphCache::new_gl(&self.context, fonts, size, metrics)?;
+        self.util_sprites = UtilSprites::new(&mut new_glyph_cache, metrics)?;
+
+        let mut glyph_cache = self.glyph_cache.borrow_mut();
+
+        // Steal the decoded image cache; without this, any animating gifs
+        // would reset back to frame 0 each time we filled the texture
+        std::mem::swap(
+            &mut glyph_cache.image_cache,
+            &mut new_glyph_cache.image_cache,
+        );
+
+        *glyph_cache = new_glyph_cache;
         Ok(())
     }
 }