Much of a layer buffer is often transparent (a stroked ring, a glow-padded
text layer, a precomp canvas), yet every destination pixel sampled it
bilinearly, and 8/16 bpc comps then re-quantised the layer's whole rotated
bounding box.
- Bilinear warps skip 16x16 source tiles whose pixels (and a one-pixel
apron) all have zero alpha: their samples are transparent and were never
drawn.
- The fast affine warp reports the rectangle it changed and, given the
comp's levels, quantises each pixel as it blends it, so draw_comp has
nothing left to re-quantise for that layer. quantize_px moves to
effectcraft-raster for this.
- quantize_rect skips runs of four all-zero (+0.0) pixels, which quantise
to themselves.
- to_rgba8 / to_rgba8_over convert row by row instead of per 4-byte item.
Every pixel stays bit-identical: tests compare the warp against the
reference path, fused quantising against quantising after blending, and
the zero-run skip against per-pixel quantising.
With the previous commit, demo comp to H.264 (`cargo xtask bench --scenario
demo --format h264 --frames 300`, 11 interleaved runs on a 16-thread Ryzen):
wall 9.26 s -> 6.97 s median (-24.8%), 8.55 s -> 6.55 s min (-23.3%); CPU
time -23%. Output byte-identical.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Dylan M. Taylor