Twelve silhouettes for a window — circle, star, speech bubble, heart, flower, hexagon, squircle, organic blob, burst badge, droplet, rounded diamond and shield — drawn by GPUI, clipped by nativeapi and given a contour shadow. The GPUI counterpart of flutter_shaped_window_example, built on the Rust binding.

cd examples/gpui_shaped_window_example
cargo run

This crate is its own cargo workspace, not a member of the root one: GPUI is a large dependency with its own platform requirements, and the root workspace's CI builds every member. It enables GPUI's runtime_shaders feature, so building on macOS does not need Xcode's Metal toolchain.

Two windows, as in the Flutter example: the 480 × 680 control window ("Outside the box.") and a 320 × 320 shaped preview beside it.

• Pick a silhouette in the 4 × 3 gallery. Each shape has its own fixed gradient, light spots and dotted texture, shared by its thumbnail and the preview. The preview morphs to the new outline over 450 ms; clicking another shape mid-morph retargets from the current frame.
• Apply shape re-applies the selected silhouette; Restore rectangle morphs back to square content and removes the native clip.
• Toggle size animates the preview between 320 and 400 px, together with its contour.
• Shadow presets None, Soft, Float, Sharp and Glow fade to their parameters over 220 ms. Adjust… swaps the gallery for the full controls: on/off, five colours, opacity (0–100 %), blur radius (0–64 px), horizontal and vertical offset (−64–64 px) and a reset to black, 30 %, 18 px, (0, 6). Sliders take a press or drag, and arrow keys / Home / End once focused. Done returns to the gallery.
• Drag the DRAG ME handle to move the preview; Tap counts clicks. Outside the silhouette, clicks go to whatever is behind it.
• Closing the control window quits.

GPUI opens the preview with no title bar and a transparent background and paints the content square; nativeapi does the rest:

src/geometry.rs is a faithful port of the Flutter example's shape_geometry.dart: the same polygons, the sampled quadratic corner arcs and the shared perimeter landmarks that make every contour (and the rectangle) morph into every other one. src/playground.rs holds the state and all native calls; src/views.rs renders both windows from it.

A few things are done differently from Flutter:

• Painting. GPUI cannot clip to a path, so the preview paints its full square and relies on the native clip; the gallery thumbnails are rasterized once (even-odd, 4 × 4 supersampled) into images. GPUI gradients take two stops, so the three-stop diagonal gradient is a quad plus a triangle meeting on the middle colour.
• Native calls outside GPUI updates. Moving, resizing or showing a window calls back into GPUI synchronously; inside an entity update GPUI cannot take those callbacks and would miss the new size. Configuration, resizes and show therefore run from a task between updates; the animations are timer-driven tasks (16 ms ticks) rather than animation controllers.
• Resizing. As in the Flutter example, the window grows once to the larger endpoint, the content and contour animate inside it, and the bounds are tightened at the end. No macOS runner channel or Impeller workaround is needed.
• Not ported: the reduced-motion setting (GPUI does not expose it — changes always animate), the chips' press-scale feedback, letter spacing on captions (not in GPUI 0.2.2's text style) and the sliders' accessibility actions.

• macOS and Windows. On macOS the clip is a content-layer mask and AppKit's alpha hit testing lets clicks outside it through; on Windows it is a window region, with a layered window behind it for the shadow.
• Not Linux: nativeapi wraps a GtkWindow* there, and GPUI does not use GTK, so the example has no native window to shape (the Flutter example's renderer-clipping plus set_input_shape path is not ported). The status line says so.