Merge PR #1056: Canvas: pages show their paper while their render is on its way, not black

ROADMAP.md

@@ -455,6 +455,7 @@ Newest first.
 - 2026-10-15: Ruler menus as InDesign's: right-clicking where the rulers meet sets the units of both; each ruler's menu lists InDesign's units and Hide Rulers, the horizontal one Delete All Guides on Spread.
 - 2026-10-15: Properties › Edit Page works as InDesign's: the Page tool on the page in view, and Properties shows that page alone (Page Size: page, preset, orientation, W/H; Margins and Columns; Quick Actions) with Back. It opened Document Setup, which changes every page.
 - 2026-10-15: Deleting pages that contain objects asks first, as InDesign does ("The affected page contains objects. Delete the page anyway?", with Don't show again), from the Pages panel, Layout › Pages › Delete Page and Properties.
+- 2026-10-15: A page scrolled or jumped to shows its paper while its render is on its way, as in InDesign, instead of the black of its shadow.
 - **2026-10-14** · The Type tool draws a new text frame over a locked empty frame, as InDesign does, instead of turning the locked frame into a text frame. No readiness percentage change.
 - **2026-10-14** · 100% black shows as pure black on screen by default, as InDesign's Appearance of Black does out of the box (Display All Blacks as Rich Black); Preferences › Appearance of Black › Display All Blacks Accurately still shows it as the dark grey it prints, and a saved choice is kept. No readiness percentage change.
 - **2026-10-14** · Pathfinder keeps the frontmost object, as InDesign does: a photo placed over shapes and intersected with them shows through the shapes (it was dropped, and the shapes kept their black fill); Add, Exclude Overlap and Minus Back take the front object's fill too, Subtract still keeps the back one. No readiness percentage change.

crates/ui-egui/src/canvas.rs

@@ -437,6 +437,15 @@ pub fn show(app: &mut DesignApp, ui: &mut egui::Ui) {
         let r = xf.rect(slot.bounds);
         painter.rect_filled(r.translate(vec2(1.5, 1.5)), 0.0, Color32::BLACK);
     }
+    // Paper under the rendered content: a page scrolled or jumped to shows its paper colour,
+    // not the shadow's black, until its render arrives.
+    let [r, g, b, _] = doc.resolve_color(designcraft_color::swatch::PAPER, 1.0).unwrap_or(designcraft_color::Color::WHITE).to_rgba8(1.0);
+    let paper = Color32::from_rgb(r, g, b);
+    for slot in &layout.slots {
+        for page in doc.spread(slot.spread).map(|sp| sp.pages.as_slice()).unwrap_or_default() {
+            painter.rect_filled(xf.rect(slot.xf.transform_rect_bbox(page.bounds())), 0.0, paper);
+        }
+    }
     // Rendered content.
     render_texture(app, ui.ctx(), rect, &xf, &layout, preview);
     if let (Some(tex), Some(sh)) = (&app.canvas.texture, app.canvas.shown) {
@@ -2833,6 +2842,39 @@ mod tests {
         assert_eq!(press(Some(up), 0.0, 1.0), 1);
     }
 
+    /// While a page's render is on its way the page shows paper, not the black of its shadow.
+    #[test]
+    fn pages_show_paper_under_their_render() {
+        let mut app = DesignApp::new(designcraft_engine::Session::new(), crate::Services::default());
+        app.run("file.new", serde_json::json!({"pages": 3, "facingPages": true})).unwrap();
+        let ctx = egui::Context::default();
+        let mut shapes = Vec::new();
+        for _ in 0..2 {
+            let raw = egui::RawInput { screen_rect: Some(Rect::from_min_size(Pos2::ZERO, vec2(1440.0, 900.0))), ..Default::default() };
+            let mut out = ctx.run_ui(raw, |ui| show(&mut app, ui));
+            out.textures_delta.clear();
+            shapes = out.shapes;
+        }
+        let st = app.session.active().unwrap();
+        let layout = CanvasLayout::new(&st.doc, false);
+        let xf = Xf::new(app.canvas_rect.unwrap(), app.view().unwrap());
+        // The paper swatch on screen (white, as the colour settings show it).
+        let [r, g, b, _] = st.doc.resolve_color(designcraft_color::swatch::PAPER, 1.0).unwrap().to_rgba8(1.0);
+        let paper: Vec<Rect> = shapes
+            .iter()
+            .filter_map(|c| match &c.shape {
+                egui::Shape::Rect(s) if s.fill == Color32::from_rgb(r, g, b) => Some(s.rect),
+                _ => None,
+            })
+            .collect();
+        // Each page on its own (a spread's pages may differ in size).
+        assert_eq!(paper.len(), st.doc.page_count());
+        for abs in 0..st.doc.page_count() {
+            let want = xf.rect(layout.page_rect(&st.doc, abs).unwrap());
+            assert!(paper.iter().any(|r| (r.min - want.min).length() < 0.01 && (r.max - want.max).length() < 0.01), "page {abs}");
+        }
+    }
+
     fn harness(app: DesignApp) -> Harness<'static, DesignApp> {
         let mut h = Harness::builder().with_size(vec2(1440.0, 900.0)).build_ui_state(
             |ui, app: &mut DesignApp| {