image: Keep texture around until new is available

Keep previous texture around during image reloads to avoid flickering.

src/widgets/image.rs

@@ -163,6 +163,7 @@ mod imp {
         /// Track changes to this image
         pub(super) file_monitor: RefCell<Option<gio::FileMonitor>>,
         pub(super) frame_buffer: Arc<SharedFrameBuffer>,
+        pub(super) previous_frame_buffer: SharedFrameBuffer,
         pub(super) decoder: RefCell<Option<Arc<Decoder>>>,
 
         /// Rotation final value (can differ from `rotation` during animation)

src/widgets/image/loading.rs

@@ -89,6 +89,7 @@ impl imp::LpImage {
             }
             DecoderUpdate::Redraw => {
                 self.set_loaded(true);
+                self.previous_frame_buffer.reset();
 
                 obj.queue_draw();
                 self.frame_buffer.rcu(|tiles| {
@@ -313,8 +314,13 @@ impl LpImage {
         self.imp().set_file_loaded(file).await;
 
         let tiles = &self.imp().frame_buffer;
+
         // Delete all stored textures for reloads
-        tiles.reset();
+        let previous_frame_buffer = tiles.reset();
+        // Store previos frames to show until new texture is loaded
+        self.imp()
+            .previous_frame_buffer
+            .swap(previous_frame_buffer.load_full());
         // Reset background color for reloads
         imp.set_background_color(None);
 

src/widgets/image/rendering.rs

@@ -126,9 +126,17 @@ impl WidgetImpl for imp::LpImage {
         );
 
         // Add texture(s)
-        self.frame_buffer
-            .load()
-            .add_to_snapshot(snapshot, applicable_zoom, &render_options);
+        let frame_buffer = self.frame_buffer.load();
+
+        // Don't use current frame buffer if it empty during an image reload
+        let use_frame_buffer = if frame_buffer.is_empty() {
+            // Fallback to previous buffer to show previous image until new one is available
+            self.previous_frame_buffer.load()
+        } else {
+            frame_buffer
+        };
+
+        use_frame_buffer.add_to_snapshot(snapshot, applicable_zoom, &render_options);
 
         snapshot.restore();
 

src/widgets/image/rotation.rs

@@ -97,8 +97,8 @@ impl LpImage {
         if self.is_best_fit() {
             let zoom_animation = imp.zoom_animation();
 
-            zoom_animation.set_value_from(dbg!(self.zoom()));
-            zoom_animation.set_value_to(dbg!(imp.zoom_level_best_fit_for_rotation(target.get())));
+            zoom_animation.set_value_from(self.zoom());
+            zoom_animation.set_value_to(imp.zoom_level_best_fit_for_rotation(target.get()));
             zoom_animation.play();
         }