show terminal background while waiting for background image to load

Avoid a "flash" of a single black but likely overly stretched and
awkwardly interpolated frame while we wait for big/animated/complex
images to load and decode.

For corrupt images, or images with an incorrect or typo'd filename in
the config, this prevents us from punting and just showing a transparent
background instead of something reasonable.

docs/changelog.md

@@ -32,6 +32,11 @@ As features stabilize some brief notes about them will accumulate here.
 * Don't hide mouse cursor when pressing only modifier keys. #3570
 * [PaneSelect](config/lua/keyassignment/PaneSelect.md) will now un-zoom to show
   all panes, then re-zoom after performing its action. #3573
+* Images, especially animated images, are now decoded in the background. When
+  used as a background layer for the terminal, we now use the normal
+  terminal background color as a placeholder until the first frame has been
+  decoded. In other circumstances, you may observe a brief black frame while
+  waiting for the image to decode.
 
 #### New
 

wezterm-gui/src/glyphcache.rs

@@ -31,6 +31,12 @@ use wezterm_font::units::*;
 use wezterm_font::{FontConfiguration, GlyphInfo, LoadedFont, LoadedFontId};
 use wezterm_term::Underline;
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum LoadState {
+    Loading,
+    Loaded,
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct CellMetricKey {
     pub pixel_width: u16,
@@ -383,6 +389,7 @@ struct FrameState {
     source: FrameSource,
     current_frame: DecodedFrame,
     frames: Vec<DecodedFrame>,
+    load_state: LoadState,
 }
 
 impl FrameState {
@@ -405,6 +412,7 @@ impl FrameState {
                 height: BLACK_SIZE,
                 duration: Duration::from_millis(0),
             },
+            load_state: LoadState::Loading,
         }
     }
 
@@ -414,6 +422,7 @@ impl FrameState {
                 Ok(frame) => {
                     self.frames.push(frame.clone());
                     self.current_frame = frame;
+                    self.load_state = LoadState::Loaded;
                     true
                 }
                 Err(TryRecvError::Empty) => false,
@@ -480,6 +489,14 @@ impl DecodedImage {
         }
     }
 
+    fn load_state(&self) -> LoadState {
+        let frames = self.frames.borrow();
+        match frames.as_ref() {
+            Some(state) => state.load_state,
+            None => LoadState::Loading,
+        }
+    }
+
     fn start_frame_decoder(lease: BlobLease, image_data: &Arc<ImageData>) -> Self {
         match FrameDecoder::start(lease.clone()) {
             Ok(rx) => Self {
@@ -854,7 +871,7 @@ impl GlyphCache {
         decoded: &DecodedImage,
         padding: Option<usize>,
         min_frame_duration: Duration,
-    ) -> anyhow::Result<(Sprite, Option<Instant>)> {
+    ) -> anyhow::Result<(Sprite, Option<Instant>, LoadState)> {
         let mut handle = DecodedImageHandle {
             h: decoded.image.data(),
             current_frame: *decoded.current_frame.borrow(),
@@ -862,12 +879,12 @@ impl GlyphCache {
         match &*handle.h {
             ImageDataType::Rgba8 { hash, .. } => {
                 if let Some(sprite) = frame_cache.get(hash) {
-                    return Ok((sprite.clone(), None));
+                    return Ok((sprite.clone(), None, decoded.load_state()));
                 }
                 let sprite = atlas.allocate_with_padding(&handle, padding)?;
                 frame_cache.insert(*hash, sprite.clone());
 
-                return Ok((sprite, None));
+                return Ok((sprite, None, decoded.load_state()));
             }
             ImageDataType::AnimRgba8 {
                 hashes,
@@ -915,7 +932,7 @@ impl GlyphCache {
                 let hash = hashes[*decoded_current_frame];
 
                 if let Some(sprite) = frame_cache.get(&hash) {
-                    return Ok((sprite.clone(), next));
+                    return Ok((sprite.clone(), next, decoded.load_state()));
                 }
 
                 let sprite = atlas.allocate_with_padding(&handle, padding)?;
@@ -928,6 +945,7 @@ impl GlyphCache {
                         *decoded_frame_start
                             + durations[*decoded_current_frame].max(min_frame_duration),
                     ),
+                    decoded.load_state(),
                 ));
             }
             ImageDataType::EncodedLease(_) | ImageDataType::EncodedFile(_) => {
@@ -967,7 +985,7 @@ impl GlyphCache {
                 let hash = frames.frame_hash();
 
                 if let Some(sprite) = frame_cache.get(&hash) {
-                    return Ok((sprite.clone(), next));
+                    return Ok((sprite.clone(), next, frames.load_state));
                 }
 
                 let frame = Image::from_raw(
@@ -982,6 +1000,7 @@ impl GlyphCache {
                 Ok((
                     sprite,
                     Some(*decoded_frame_start + frames.frame_duration().max(min_frame_duration)),
+                    frames.load_state,
                 ))
             }
         }
@@ -991,7 +1010,7 @@ impl GlyphCache {
         &mut self,
         image_data: &Arc<ImageData>,
         padding: Option<usize>,
-    ) -> anyhow::Result<(Sprite, Option<Instant>)> {
+    ) -> anyhow::Result<(Sprite, Option<Instant>, LoadState)> {
         let hash = image_data.hash();
 
         if let Some(decoded) = self.image_cache.get(&hash) {

wezterm-gui/src/termwindow/background.rs

@@ -1,4 +1,5 @@
 use crate::color::LinearRgba;
+use crate::glyphcache::LoadState;
 use crate::quad::{QuadAllocator, QuadTrait};
 use crate::termwindow::RenderState;
 use crate::utilsprites::RenderMetrics;
@@ -397,15 +398,17 @@ impl crate::TermWindow {
         &self,
         bg_color: LinearRgba,
         top: StableRowIndex,
-    ) -> anyhow::Result<()> {
+    ) -> anyhow::Result<bool> {
         let gl_state = self.render_state.as_ref().unwrap();
         let mut layer_idx = -127;
+        let mut loaded_any = false;
         for layer in self.window_background.iter() {
             if self.render_background(gl_state, bg_color, layer, layer_idx, top)? {
+                loaded_any = true;
                 layer_idx = layer_idx.saturating_add(1);
             }
         }
-        Ok(())
+        Ok(loaded_any)
     }
 
     fn render_background(
@@ -422,12 +425,16 @@ impl crate::TermWindow {
 
         let color = bg_color.mul_alpha(layer.def.opacity);
 
-        let (sprite, next_due) = gl_state
+        let (sprite, next_due, load_state) = gl_state
             .glyph_cache
             .borrow_mut()
             .cached_image(&layer.source, None)?;
         self.update_next_frame_time(next_due);
 
+        if load_state == LoadState::Loading {
+            return Ok(false);
+        }
+
         let pixel_width = self.dimensions.pixel_width as f32;
         let pixel_height = self.dimensions.pixel_height as f32;
         let pixel_aspect = pixel_width / pixel_height;

wezterm-gui/src/termwindow/render/mod.rs

@@ -432,7 +432,7 @@ impl crate::TermWindow {
             padding.next_power_of_two()
         };
 
-        let (sprite, next_due) = gl_state
+        let (sprite, next_due, _load_state) = gl_state
             .glyph_cache
             .borrow_mut()
             .cached_image(image.image_data(), Some(padding))?;

wezterm-gui/src/termwindow/render/paint.rs

@@ -171,6 +171,8 @@ impl crate::TermWindow {
         log::trace!("quad map elapsed {:?}", start.elapsed());
         metrics::histogram!("quad.map", start.elapsed());
 
+        let mut paint_terminal_background = false;
+
         // Render the full window background
         match (self.window_background.is_empty(), self.allow_images) {
             (false, true) => {
@@ -185,8 +187,16 @@ impl crate::TermWindow {
                     })
                     .unwrap_or(0);
 
-                self.render_backgrounds(bg_color, top)
+                let loaded_any = self
+                    .render_backgrounds(bg_color, top)
                     .context("render_backgrounds")?;
+
+                if !loaded_any {
+                    // Either there was a problem loading the background(s)
+                    // or they haven't finished loading yet.
+                    // Use the regular terminal background until that changes.
+                    paint_terminal_background = true;
+                }
             }
             _ if window_is_transparent => {
                 // Avoid doubling up the background color: the panes
@@ -194,6 +204,11 @@ impl crate::TermWindow {
                 // should be no gaps that need filling in
             }
             _ => {
+                paint_terminal_background = true;
+            }
+        }
+
+        if paint_terminal_background {
             // Regular window background color
             let background = if panes.len() == 1 {
                 // If we're the only pane, use the pane's palette
@@ -218,7 +233,6 @@ impl crate::TermWindow {
             )
             .context("filled_rectangle for window background")?;
         }
-        }
 
         for pos in panes {
             if pos.is_active {