Trait PreviewCompositor 

pub trait PreviewCompositor: Send {
    // Required method
    fn composite(
        &mut self,
        layers: &[(&RealtimeLayer, &VideoFrame)],
        canvas: (u32, u32),
        t: Duration,
    ) -> Option<(Vec<u8>, u32, u32)>;

    // Provided methods
    fn blend(
        &mut self,
        kind: XfadeTransition,
        a: &[u8],
        b: &[u8],
        progress: f32,
        w: u32,
        h: u32,
    ) -> Option<Vec<u8>> { ... }
    fn reset_effects(&mut self) { ... }
}

An external compositor the preview runner can use in place of its built-in CPU compositor. Implemented by avio over ff-render; see the module docs.

Required Methods

fn composite( &mut self, layers: &[(&RealtimeLayer, &VideoFrame)], canvas: (u32, u32), t: Duration, ) -> Option<(Vec<u8>, u32, u32)>

Composite layers (bottom to top, paired with each layer’s decoded rgba frame) into a single rgba frame at timeline time t, targeting the canvas output size.

Returns Some((rgba, width, height)) on success, or None to fall back to the runner’s CPU compositor (an unsupported layer, no adapter, or a GPU error). Returning None must never leave the runner in a bad state.

Provided Methods

fn blend( &mut self, kind: XfadeTransition, a: &[u8], b: &[u8], progress: f32, w: u32, h: u32, ) -> Option<Vec<u8>>

Blend the outgoing frame a into the incoming frame b at progress (0 = all a, 1 = all b) for the xfade kind, both packed RGBA of w * h * 4 bytes.

Returns Some(rgba) on success, or None to leave the frame to the runner’s CPU apply_xfade — which is the answer for a kind the implementor does not render, a missing adapter, a GPU error, and a kind it renders correctly but slower. Declining must never leave the runner in a bad state.

Defaults to None, so an implementor that only composites is unaffected.

This sits beside composite rather than in a trait of its own because both exist for the same reason — reaching ff-render, which depends on this crate — and one injected object means one GPU context rather than two.

fn reset_effects(&mut self)

Drops whatever the implementor carries from one clip into the next.

The runner calls this when playback crosses a clip boundary. It exists for a stateful effect: motion blur accumulates an exposure trail across the frames of one clip, and without a reset at the cut the outgoing clip’s trail bleeds into the incoming clip’s first frame. The export path has always done this; playback did not, which is what #1705 fixes.

Defaults to a no-op, so an implementor that carries nothing across frames is unaffected.

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors