Fix image-fill mapping: anchor to the fill's bounding box

The renderer painted the image brush at its native origin (0,0) with no brush
transform, so an image-filled rect drawn anywhere but the world origin only showed
the overlapping corner of the image. Both render paths now map the image's native
pixel space onto the fill's bounding box (Vello brush_transform; tiny-skia Pattern
transform) — 1:1 for an image-sized rectangle, stretch-to-bbox for arbitrary shapes.

lightningbeam-ui/lightningbeam-core/src/renderer.rs

@@ -1162,7 +1162,15 @@ pub fn render_vector_graph(
             if let Some(image_asset) = document.get_image_asset(&image_asset_id) {
                 if let Some(image) = image_cache.get_or_decode(image_asset) {
                     let image_with_alpha = (*image).clone().with_alpha(opacity_f32);
-                    scene.fill(fill_rule, base_transform, &image_with_alpha, None, &path);
+                    // Map the image (native pixel space, origin 0,0) onto the fill's
+                    // bounding box, so it sits where the shape is and scales to fit
+                    // (1:1 for an image-sized rectangle).
+                    let bbox = vello::kurbo::Shape::bounding_box(&path);
+                    let iw = (image_asset.width.max(1)) as f64;
+                    let ih = (image_asset.height.max(1)) as f64;
+                    let brush_transform = Affine::translate((bbox.x0, bbox.y0))
+                        * Affine::scale_non_uniform(bbox.width() / iw, bbox.height() / ih);
+                    scene.fill(fill_rule, base_transform, &image_with_alpha, Some(brush_transform), &path);
                     filled = true;
                 }
             }
@@ -1486,12 +1494,21 @@ fn render_vector_graph_cpu(
         if let Some(image_asset_id) = fill.image_fill {
             if let Some(asset) = document.get_image_asset(&image_asset_id) {
                 if let Some(img_pixmap) = image_cache.get_or_decode_cpu(asset) {
+                    // Map the image's native pixel space onto the fill's bounding box.
+                    let bbox: kurbo::Rect = vello::kurbo::Shape::bounding_box(&path);
+                    let iw = (asset.width.max(1)) as f32;
+                    let ih = (asset.height.max(1)) as f32;
+                    let sx = (bbox.width() as f32) / iw;
+                    let sy = (bbox.height() as f32) / ih;
+                    let pat_tf = tiny_skia::Transform::from_row(
+                        sx, 0.0, 0.0, sy, bbox.x0 as f32, bbox.y0 as f32,
+                    );
                     let pattern = tiny_skia::Pattern::new(
                         tiny_skia::Pixmap::as_ref(&img_pixmap),
                         tiny_skia::SpreadMode::Pad,
                         tiny_skia::FilterQuality::Bilinear,
                         opacity,
-                        tiny_skia::Transform::identity(),
+                        pat_tf,
                     );
                     let mut paint = tiny_skia::Paint::default();
                     paint.shader = pattern;