Merge pull request #1886 from sbjwin/fix/thumbnail-grayscale

UI: follow Grayscale view mode in slide thumbnails

crates/ui-egui/src/backstage/print.rs

@@ -207,7 +207,8 @@ fn preview(app: &mut SlideApp, ui: &mut Ui, bs: &mut Backstage, doc: &deckcraft_
     let mut budget = 4u32;
     let mut draw_slide = |ui: &mut Ui, i: usize, r: Rect| {
         let px = (r.width() * ui.ctx().pixels_per_point()).round().clamp(16.0, 1600.0) as u32;
-        match app.textures.thumb(ui.ctx(), doc, i, px, &mut budget) {
+        // Print preview matches the actual exported PDF output (always full color).
+        match app.textures.thumb(ui.ctx(), doc, i, px, false, &mut budget) {
             Some(tex) => {
                 ui.painter().image(tex.id(), r, Rect::from_min_max(pos2(0.0, 0.0), pos2(1.0, 1.0)), Color32::WHITE);
             }

crates/ui-egui/src/canvas.rs

@@ -299,7 +299,7 @@ pub fn show(app: &mut SlideApp, ui: &mut Ui) {
             vec2(w as f32 * scale, h as f32 * scale),
         );
         let mut budget = 2;
-        if let Some(tex) = app.textures.thumb(ui.ctx(), &doc, idx, (r.width() * ppp).round().max(1.0) as u32, &mut budget) {
+        if let Some(tex) = app.textures.thumb(ui.ctx(), &doc, idx, (r.width() * ppp).round().max(1.0) as u32, app.ui.grayscale, &mut budget) {
             painter.image(tex.id(), r, Rect::from_min_max(pos2(0.0, 0.0), pos2(1.0, 1.0)), Color32::WHITE);
         }
     }

crates/ui-egui/src/panels/thumbs.rs

@@ -219,7 +219,7 @@ fn list(app: &mut SlideApp, ui: &mut Ui) {
         // Only rows in view (plus a little margin) ask for a thumbnail: with every row asking, a
         // deck bigger than the thumbnail cache evicts its own thumbnails and never settles (#969).
         let near = ui.clip_rect().expand2(vec2(0.0, 2.0 * row.height())).intersects(row);
-        let tex = if near { app.textures.thumb(ui.ctx(), &doc, i, wpx, &mut budget) } else { None };
+        let tex = if near { app.textures.thumb(ui.ctx(), &doc, i, wpx, app.ui.grayscale, &mut budget) } else { None };
         match tex {
             Some(tex) => {
                 p.image(

crates/ui-egui/src/sorter.rs

@@ -209,7 +209,8 @@ fn place_slides(app: &mut SlideApp, ui: &mut Ui, g: &Grid<'_>, budget: &mut u32,
                 // Only cells in view (plus a little margin) ask for a thumbnail, so a deck bigger
                 // than the thumbnail cache does not evict its own thumbnails forever (#969).
                 let near = ui.clip_rect().expand2(vec2(0.0, 2.0 * cell.height())).intersects(cell);
-                let tex = if near { app.textures.thumb(ui.ctx(), g.doc, i, (img.width() * ppp).round() as u32, budget) } else { None };
+                let tex =
+                    if near { app.textures.thumb(ui.ctx(), g.doc, i, (img.width() * ppp).round() as u32, app.ui.grayscale, budget) } else { None };
                 match tex {
                     Some(tex) => {
                         p.image(tex.id(), img, Rect::from_min_max(pos2(0.0, 0.0), pos2(1.0, 1.0)), Color32::WHITE);
@@ -391,7 +392,7 @@ pub fn notes_page(app: &mut SlideApp, ui: &mut Ui) {
     }
     let ppp = ui.ctx().pixels_per_point();
     let mut budget = 2;
-    if let Some(tex) = app.textures.thumb(ui.ctx(), &doc, idx, (srect.width() * ppp).round() as u32, &mut budget) {
+    if let Some(tex) = app.textures.thumb(ui.ctx(), &doc, idx, (srect.width() * ppp).round() as u32, app.ui.grayscale, &mut budget) {
         ui.painter().image(tex.id(), srect, Rect::from_min_max(pos2(0.0, 0.0), pos2(1.0, 1.0)), Color32::WHITE);
     }
     ui.painter().rect_stroke(srect, CornerRadius::ZERO, Stroke::new(1.0, Color32::GRAY), egui::StrokeKind::Outside);

crates/ui-egui/src/textures.rs

@@ -361,9 +361,19 @@ impl Textures {
         self.thumbs.clear();
     }
 
-    /// A thumbnail texture; renders at most `budget` new thumbnails per frame (returns None when
-    /// it is over budget, so the caller draws a placeholder and asks for another frame).
-    pub fn thumb(&mut self, ctx: &egui::Context, p: &Presentation, index: usize, width_px: u32, budget: &mut u32) -> Option<TextureHandle> {
+    /// A thumbnail texture; renders at most `budget` new thumbnails per frame. Over budget it
+    /// returns the slide's previous thumbnail if there is one (and asks for another frame), else
+    /// None, so the caller draws a placeholder.
+    /// When `grayscale` is true, the thumbnail renders in black-and-white (matching Grayscale view).
+    pub fn thumb(
+        &mut self,
+        ctx: &egui::Context,
+        p: &Presentation,
+        index: usize,
+        width_px: u32,
+        grayscale: bool,
+        budget: &mut u32,
+    ) -> Option<TextureHandle> {
         let slide = p.slides.get(index)?.clone();
         let master = master_of(p, &slide);
         let h = (width_px as f64 * p.slide_size.height / p.slide_size.width.max(1.0)).round().max(1.0) as u32;
@@ -372,7 +382,7 @@ impl Textures {
             master: master.as_ref().map(|m| Arc::as_ptr(m) as usize).unwrap_or(0),
             size: (width_px, h),
             edit: false,
-            extra: 0,
+            extra: grayscale as u64,
             want: Region::slide(width_px, h),
             editing_text: None,
         };
@@ -385,7 +395,8 @@ impl Textures {
             return Some(e.tex.clone());
         }
         if *budget == 0 {
-            // Keep showing the stale thumbnail while the new one waits.
+            // Keep showing the stale thumbnail while the new one waits; request a repaint to finish rendering.
+            ctx.request_repaint();
             return self.thumbs.get(&key.slide).map(|e| e.tex.clone());
         }
         *budget -= 1;
@@ -393,7 +404,7 @@ impl Textures {
         let scale = tw as f64 / p.slide_size.width.max(1.0);
         let img = deckcraft_render::render_slide(p, index, &RenderOpts { scale, size: Some((tw, th)), threads: 0, ..Default::default() });
         self.thumb_renders += 1;
-        let tex = upload_editor(ctx, format!("thumb-{index}"), to_color_image(&img, false));
+        let tex = upload_editor(ctx, format!("thumb-{index}"), to_color_image(&img, grayscale));
         // Drop the old entry for this slide address; entries for slides that no longer exist age out.
         let region = key.want;
         self.thumbs.insert(key.slide, Entry { key, tex: tex.clone(), region, _slide: slide, _master: master, stamp: clock });
@@ -433,6 +444,20 @@ mod tests {
         assert_eq!(device_pixel_rect(aligned, ppp), aligned);
     }
 
+    #[test]
+    fn to_color_image_turns_colors_to_grayscale_when_flag_is_set() {
+        let img = deckcraft_render::Image { width: 2, height: 1, pixels: vec![0, 0, 255, 255, 255, 0, 0, 255] };
+        let color = super::to_color_image(&img, false);
+        assert_eq!(color.pixels[0], egui::Color32::from_rgba_premultiplied(0, 0, 255, 255));
+        assert_eq!(color.pixels[1], egui::Color32::from_rgba_premultiplied(255, 0, 0, 255));
+
+        let gray = super::to_color_image(&img, true);
+        assert_eq!(gray.pixels[0].r(), gray.pixels[0].g());
+        assert_eq!(gray.pixels[0].g(), gray.pixels[0].b());
+        assert_eq!(gray.pixels[1].r(), gray.pixels[1].g());
+        assert_eq!(gray.pixels[1].g(), gray.pixels[1].b());
+    }
+
     #[test]
     fn a_bad_scale_does_not_move_the_rect() {
         let r = Rect::from_min_size(pos2(3.0, 4.0), vec2(10.0, 12.0));