preview — overview

A native winit window with a wgpu surface that wisp renders into. Plays an MP4 end-to-end through the decode → playback → wisp stack:

sequenceDiagram
    participant Window as winit::Window
    participant Wgpu as wgpu Instance /<br/>Adapter / Device / Queue
    participant App as wisp::Application<br/>(from_wgpu)
    participant Surface as wgpu::Surface
    participant Player
    participant Stage
    participant Renderer

    Note over Window,Wgpu: boot
    Window ->> Wgpu: create_surface(window)
    Wgpu ->> App: from_wgpu(instance, adapter, device, queue)
    Wgpu ->> Surface: configure(width, height, format)

    loop Per RedrawRequested
        Window ->> Player: tick(dt)
        Note over Player: uploads next frame<br/>to VideoTexture
        Player ->> Stage: build one-Sprite scene<br/>(centered, aspect-fit)
        Stage ->> Renderer: render_stage(surface_view)
        Renderer ->> Surface: surface_texture.present()
    end

Why it exists

The recorder's editor view is a native sibling window — not the Tauri webview — because GPU-accelerated 4K video preview behind WebKit's compositor isn't a viable path. preview proves the contract: wisp can attach to a host-supplied wgpu device and render every frame into the host's surface.

Application::from_wgpu is the seam. The Tauri shell will wire two separate windows (the WebKit-backed shell window + a winit-backed preview window) and hand wisp the wgpu objects from the latter.

Run it

# Default fixture (committed test MP4):
cargo run -p preview

# Custom video:
cargo run -p preview -- /path/to/video.mp4

The window title is screen — preview. Close it to exit; playback will also auto-exit when the stream reaches EOF.

Headless asset generator

render_offscreen is the same pipeline driven against a RenderTexture instead of a winit surface. Used both as the chapter's PNG source and as a CI-safe smoke test for the from_wgpu codepath:

cargo run -p preview --example render_offscreen

Anti-regression

• aspect_fit_scale is unit-tested for matching/wider/taller/zero cases.
• tests/render_smoke.rs exercises the full Application::from_wgpu → Player → Renderer → RenderTexture path and asserts the rendered output is non-trivial (not the clear color, not uniform).