A 1-D indirect dispatch of ceil(W*H/64) workgroups for the wavefront
TRACE/SHADE stages overflows maxComputeWorkgroupsPerDimension (65535 on
Dawn/Firefox) once the surface exceeds ~4.19M rays (~2560x1640). Per the
WebGPU spec such a dispatch is silently dropped — no validation error —
so at 4K the world is never traced and the accumulator stays black while
non-RT passes survive.
_wfPrep now spreads the workgroups across a 2-D grid (x clamped to 65535,
y = ceil(wg/65535)), and the wfTrace/wfShade entry points rebuild the
linear ray index from (global_invocation_id, num_workgroups). The existing
`i >= _wfCurCount()` guard absorbs the grid overshoot. GENERATE/RESOLVE
already use a 2-D tile dispatch and are unchanged.
Verified in Firefox/WebGPU with RTStress at a 3449x1739 surface (5.99M
rays, 93716 workgroups — well over the 65535 cap): renders the full cube
grid where master shows a black screen.
Resolves#11
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
