Render: a picture's shadow covers the whole picture

The shadow of a picture is the picture recoloured to the shadow colour,
but drawing the picture left its pixel-space transform set, so the
recolouring rectangle (sized in points) covered only part of a picture
whose bitmap is bigger than it is shown: a 400 px photo at 240 pt cast a
shadow of its top-left corner only. The shape's transform is restored
before recolouring.

Wild synthetic set: framed pictures with shadows 7.67 -> 5.95, rotated
picture with a shadow 10.67 -> 10.07.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

crates/render/src/lib.rs

@@ -1224,6 +1224,9 @@ impl Renderer {
                 Some(pf) => {
                     ctx.push_clip_layer(&silhouette);
                     paint::picture(ctx, rctx.pres, pf, Rect::new(0.0, 0.0, w, h), sm, None);
+                    // Drawing the picture leaves its own pixel transform set: back to the shape's,
+                    // or the recolouring below covers only part of a large picture's shadow.
+                    ctx.set_transform(sm);
                     ctx.push_layer(None, Some(peniko::BlendMode::new(peniko::Mix::Normal, peniko::Compose::SrcIn)), None, None, None);
                     ctx.set_paint(color(c.with_alpha(255), 1.0));
                     ctx.fill_rect(&Rect::new(0.0, 0.0, w, h).inflate(1.0, 1.0));

crates/render/src/tests_wild.rs

@@ -598,3 +598,37 @@ fn table_borders_take_their_dashes_and_diagonals_are_drawn() {
     // The diagonal from top-left to bottom-right passes through the middle.
     assert!(close(img.pixel(200, 150), Rgba::rgb(0, 0, 255), 40), "{:?}", img.pixel(200, 150));
 }
+
+#[test]
+fn a_large_pictures_shadow_is_whole() {
+    // A 400 px picture shown at 240 pt: its shadow was recoloured in the picture's pixel space and
+    // covered only part of it.
+    let mut counts = vec![];
+    for side in [8u32, 400] {
+        let mut p = Presentation::default();
+        let media = p.add_media("image1.png", "image/png", png(side, side * 3 / 4, [0, 0, 255]));
+        let mut fx = offset_shadow();
+        if let Some(o) = &mut fx.outer_shadow {
+            o.blur = 8.0;
+        }
+        let sh = Shape {
+            id: ShapeId(15),
+            xfrm: Some(Xfrm { rot: 20.0, ..Xfrm::new(360.0, 300.0, 240.0, 160.0) }),
+            kind: ShapeKind::Picture { fill: deckcraft_model::style::PictureFill { media, ..Default::default() } },
+            effects: Some(fx),
+            ..Default::default()
+        };
+        std::sync::Arc::make_mut(&mut p.slides[0]).shapes = vec![sh];
+        let img = render_slide(&p, 0, &RenderOpts { scale: 1.0, ..Default::default() });
+        counts.push(
+            (0..img.height)
+                .flat_map(|y| (0..img.width).map(move |x| (x, y)))
+                .filter(|(x, y)| {
+                    let q = img.pixel(*x, *y);
+                    q[0] < 200 && q[2] < 200
+                })
+                .count(),
+        );
+    }
+    assert!(counts[1] > 3000 && (counts[0] as i64 - counts[1] as i64).abs() < 300, "{counts:?}");
+}