@refrain-lyre/render-soft

CPU reference software rasterizer. Consumes the deformed geometry and draw order produced by @refrain-lyre/core and rasterizes into the canonical premultiplied-alpha model surface (§8.3) entirely on the CPU — float64 accumulation, quantized to RGBA8 once at readback. The surface is extended premultiplied: additive layers may retain RGB greater than alpha, including emissive RGB at zero alpha.

This renderer defines the conformance goldens (§12): it is deterministic on any machine, needs no GPU in CI, and implements the normative blend and mask equations exactly. @refrain-lyre/render-webgl is verified against its output within the §12 tolerance. It is browser-safe, with only @refrain-lyre/core as a peer and no platform-specific runtime dependency, so the testbed can diff GPU output against it live.

The normative rasterization rules are in §8.3.1: pixel-center sampling, top-left fill, no MSAA, and bilinear filtering of premultiplied texels clamped to the selected crop. Mask groups rasterize m = 1 − ∏(1 − aᵢ) coverage from deformed geometry and raw texture alpha only (§8.4).

See the specification.