All 27 blend modes now composite on the GPU instead of sending the
whole frame to the CPU.
- render::plan: PlanLayer carries its Blend; plan_frame no longer falls
back to a CPU frame for non-Normal modes. Media, graphic clips,
multicam angles and CPU-rendered layer images (standard effects) keep
their clip's mode; inside a transition the mode is Normal, as in the
CPU reference. execute_cpu composites with each layer's mode.
- gpu: Normal keeps the single fixed-function pass. Dissolve also uses
fixed-function "over": the CPU's 64-bit pixel hash is reproduced in
WGSL on u32 pairs (pattern bit-exact). The other 25 modes copy the
accumulator region under the layer's quad into a backdrop texture and
composite in fs_blend with the CPU math (sRGB-encoded straight colour,
W3C formulas, back to linear, same premultiplied mix and clamping).
- Tests: per-mode GPU-vs-CPU parity (gpu crate: overlapping transformed
layers, partial opacity/alpha, empty/partial backdrop; golden: every
mode through plan_frame incl. an effect layer, blended clips in a
cross dissolve), exact-value edge cases (black/white, Divide by 0,
Dodge/Burn at 0 and 1, zero alpha) within 4.9e-4, Dissolve pattern
exact, off-output layers, quad bounds.
- Bench: new stack3-blend playback scenario (V2 Screen, V3 Overlay);
CPU ms/frame 151-214 -> 86-89, Full 19/173 and 138/54 -> 191/1, 192/0.
- Docs: architecture §5, gpu crate docs, testing, performance.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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