- LayerBlend: a plain layer is blended straight from its texture in one pass
instead of a Content pass to a scratch chunk and a Blend pass.
- fs_layerbatch: runs of up to four plain layers that only feed each other
are drawn as one pass, reading and writing the chunk once (the uniform
record grows to its 256-byte stride to hold the extra layers).
- Drop shadows and outer glows alone: the merge builds the layer from its
shape (F_LAYER_SHAPE), and nothing is copied back when the effect region
covers the canvas. Such a layer takes 3 passes instead of 6.
- fs_layerbatch_normal: runs of Normal layers use a shader with Normal's code
alone. Per-pass timestamps showed the batch spent 80% of its time on the
register cost of carrying every blend mode, not on the arithmetic; Normal
goes through the same function in every shader, so a layer gives the same
bits whichever pass draws it.
P60 / P61 with the GPU compositor (8 GB budget, M4 Pro): 111 / 113 ms ->
28.2 / 28.1 ms. With the app's default Memory Usage these documents still
fall back to the CPU compositor on unified memory, so the budgets stay
unenforced.
Output: over the GPU parity suite (1620 renders) 1038 are bit-identical to
before and the rest differ by at most 1e-4/255, except one pixel one 8-bit
step apart where an adjustment rounds at .5; the mean difference from the CPU
reference is unchanged. New parity tests cover runs of every mode, Normal
runs at 8/16/32-bit and Lab, and exterior effects at any fill.
Akos Arinton