The cross product of two tangents, each the difference of the de
Casteljau's last two points: the row's along u, and the columns' last
points evaluated along u for v. The lerps pass their operand through at
the patch edges. Vertex normals stay unused (gpu/probe exp142-143).
Patch normals are now also generated for shade mapping with lighting
off, on every backend: the GE uses them there too.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>