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A layer with Blending Options › Blend If made the planner refuse the whole document, so every refresh of it ran the CPU compositor: on the #209 layered document an opacity edit took 140 ms instead of 6 ms. Blend If is compose::apply_blend_if: the composite with the layer mixed back towards the backdrop by a per-pixel weight from the layer's own content with its masks ("This Layer"; an adjustment's result) and the backdrop ("Underlying Layer"). The planner now keeps the backdrop, composites the layer as before (channel restrictions included, as on the CPU), renders its own content and emits one Lerp pass with the new F_BLEND_IF flag and the ranges packed exactly in its parameters. Base and clipped layers both go through it; Advanced Blending still falls back to the CPU. Hard points: compositing can leave an 8-bit level a few millionths below itself (a level-20 backdrop at partial alpha reads 19.999998), which put it on the wrong side of a hard point at that level on the CPU, and the GPU's arithmetic differs there. Both now treat a value within 1e-4 of a level as that level; 8/16-bit values off a level are at least 1/257 away. On 16/32-bit documents the GPU reads layers as RGBA16F, so a value within about a tenth of a level of a hard point can still land on the other side, as with the GPU Threshold adjustment. Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com> Co-authored-by: Brandon Thomas <echelon@gmail.com>