image: Keep texture around until new is available

Keep previous texture around during image reloads to avoid flickering.

news.d/47.rc/fixed-avoid-flickering-when-reloading-image

@@ -0,0 +1 @@
+Flickering while images are reloaded. Instead, keep the old textures around until a new texture is available.

src/decoder/tiling.rs

@@ -177,19 +177,18 @@ impl FrameBuffer {
         self.current().cleanup(zoom, viewport);
     }
 
-    /// Delete all stored information
-    ///
-    /// Used when reloading image
-    pub fn reset(&mut self) {
-        self.update_sender = None;
-        self.images.clear();
-    }
-
     pub fn contains(&self, zoom: f64, coordinates: Coordinates) -> bool {
         self.images
             .front()
             .map_or(false, |x| x.contains(zoom, coordinates))
     }
+
+    /// Returns true if there are no textures
+    pub fn is_empty(&self) -> bool {
+        self.images
+            .front()
+            .map_or(false, |x| x.tile_layers.is_empty())
+    }
 }
 
 #[derive(Clone, Debug, Default)]
@@ -623,12 +622,15 @@ impl SharedFrameBuffer {
         });
     }
 
-    pub fn reset(&self) {
-        self.buffer.rcu(|tiling_store| {
-            let mut new_store = (**tiling_store).clone();
-            new_store.reset();
-            Arc::new(new_store)
-        });
+    /// Reset to default and return old store
+    ///
+    /// Used when reloading images
+    pub fn reset(&self) -> Self {
+        let old_buffer = self.buffer.swap(Default::default());
+
+        Self {
+            buffer: ArcSwap::new(old_buffer),
+        }
     }
 
     pub fn get_layer_tiling_or_default(&self, zoom: f64, viewport: graphene::Rect) -> Tiling {

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();
         }