Three GPUI windows laid out on the primary display by nativeapi: WindowManager::set_will_show_hook catches each window just before it is shown, sizes and positions it against Display::work_area, and then lets the show through with WindowManager::call_original_show — the GPUI counterpart of flutter_multiple_window_example, built on the Rust binding.

cd examples/gpui_multiple_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.

The three windows cover 60% of the work area, centred: Primary Window takes the top row (full width, half the height); Secondary Window and Tertiary Window share the bottom row, left and right.

A Window in the primary window does what the Flutter button does: it finds the window titled Primary Window through WindowManager::get_all, makes it 1000 × 1000 and shows it — and the will-show hook puts it straight back into its slot.

A will-show hook replaces the platform's show: a window whose hook does not call WindowManager::call_original_show(id) never appears.

On macOS the hook swizzles -[NSWindow makeKeyAndOrderFront:], and GPUI calls exactly that inside open_window (for focus: true, show: true, the default), after setting the title. So yes, the hook fires for GPUI's show, and the window is already registered with nativeapi then (WindowManager::get enumerates NSApp.windows). But right after that call GPUI moves the window back to the origin it was asked for (setFrameTopLeftPoint: in MacWindow::open), so only the hook's size sticks, not its position: all three windows end up at GPUI's centred origin.

The example therefore opens the windows with show: false and shows them with nativeapi's Window::show from a GPUI task. That show goes through the same hook, and nothing moves the window afterwards. The task matters too: the hook resizes the window, and GPUI only hears about a resize when none of its updates is running.

(With focus: false GPUI shows a window with orderFront:, which the hook does not catch at all. How the hook meets GPUI's show on Windows has not been checked.)

• The will-hide hook logs, like Flutter's, but then also calls call_original_hide: a hook replaces the hide just like the show, and the Flutter example's hook, which only prints, would keep any hide from happening.
• Closing the last window quits the app.
• The Material app bar is a plain GPUI header under the native title bar.

• macOS and Windows. Checked on macOS (layout against the work area); not run on Windows.
• The hook fires twice per Window::show on macOS (seen in a log; presumably -setIsVisible:YES, which Window::show calls first, goes through makeKeyAndOrderFront: too). Harmless here, since the layout is idempotent.
• Not Linux: nativeapi wraps a GtkWindow* there, and GPUI does not use GTK, so the example has no native windows to work with.