Render an Off-Screen Frame

This complete program uses desktop artwork but does not move or hide icons. It renders at an exact timestamp and reports the resulting buffer. Install the two library crates and run it in an interactive Windows session with at least one desktop icon.

use rdi_core::{Canvas, Curve, DesktopController, Duration, IconAnimationSpec,
    OverlayRenderOptions, Point, Scene, SceneIcon};
use rdi_platform_windows::WindowsBackend;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let controller = DesktopController::new(WindowsBackend::new())?;
    let icon = controller.list_icons()?.into_iter().next()
        .ok_or("At least one desktop icon is needed for artwork")?;
    let scene = Scene {
        canvas: Canvas { width: 640, height: 240, dpi_scale: 1.0, icon_size: 48 },
        icons: vec![SceneIcon {
            origin: Point::new(60, 80),
            animation: IconAnimationSpec::new(
                icon.id, Point::new(500, 80),
                Duration::Fixed(std::time::Duration::from_secs(2)),
                Curve::ease_in_out(),
            ),
        }],
        render_options: OverlayRenderOptions::default(),
    };
    let session = controller.prepare_scene(scene)?;
    let frame = session.render_at(1.0)?;
    session.close()?;
    assert_eq!(frame.pixels.len(), frame.width as usize * frame.height as usize * 4);
    println!("{}x{} at {}s: {} bytes", frame.width, frame.height,
        frame.seconds, frame.pixels.len());
    Ok(())
}

For a sequence, retain the session and render at frame_index / fps, bounded by session.duration. Earlier timestamps reproduce earlier states without sleeping. Attach a shader effect before preparing the scene.

The bytes are premultiplied BGRA8, not PNG data. Before giving them to a straight-alpha RGBA encoder, reorder channels and unpremultiply nonzero-alpha RGB (set RGB to zero for zero alpha). The rendering contract describes limits and coordinates; the Python PNG example shows conversion through an existing decoder.