Step 3 of the wire pipeline cold-open optimization plan — the biggest
single lever.
Each segment used to upload as 6 vertices × 96 B = 576 B with the segment
payload (pos_a/pos_b/color/half_width/distance/pattern_length/pat0/pat1)
duplicated across all six corners of the quad. Wire pipeline now uploads
one INSTANCE per segment (88 B) and the vertex shader derives `which_end`
and `side` from `@builtin(vertex_index)` against a 6-entry corner table.
Net effect on cold open: ~6.5× less wire vertex memory and PCIe upload,
plus a smaller Vec to allocate and copy on the CPU side.
Wire instance attributes also collapse distance_a / distance_b into a
single mix() inside the vertex shader, so per-segment distance still
interpolates correctly for the GPU-side linetype dash test.
Touches the wire, wire_xray, and face3d-edges draw passes.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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