Campaign V slice V6e, second of three. Billboard particles and mesh particles
are the last two pairs blocked on the texture-table shape; sky follows.
particle takes the same treatment mesh_modern took: the `flat uvec2` handle
varying becomes a `flat uint` slot and the fragment stage samples through
ACDREAM_SAMPLE_ARRAY. What is different here is the untextured particle. The
shader used to ask "is the handle I was given zero", which GL can answer because
its emulated table stores handles; Vulkan cannot, because set 2 is an opaque
descriptor array and reading an element nobody wrote is undefined rather than
zero. So the question moves to the index: the CPU writes ACDREAM_TEXTURE_NONE
for a particle with no texture instead of interning the null handle as a table
slot, and both dialects test the same value. GL renders identically — the same
particles take the same branch to the same procedural blob — and the handle
table simply stops carrying an entry that never named a texture. A test pins the
sentinel across all three declarations of it, because a silent disagreement here
would sample slot 0xFFFFFFFF instead of drawing the blob.
particle_mesh needed no restructuring, only names. Vulkan GLSL has no default
uniform block, so `uniform uint uTextureIndex;` is not unsupported but
unspellable, and the two values are per-pass — one texture and one layer for a
whole sub-batch — which is exactly what the shared push-constant block is for.
uTextureIndex becomes uTextureIndexA; uTextureLayer becomes uParamA, which was
the spare scalar and is a natural fit because the shader converted the layer to
float anyway. The widening moved from the shader to the CPU; layers are small
integers, so the sampled value is bit-identical.
Gates: Release build clean; App tests 4,058 passed / 3 skipped (baseline 4,057
plus the sentinel drift guard). Offline pixel gate against 95f8c25f: two
captures, 29 px and 21 px of 563,200 compared (3.73e-05 and 5.15e-05), with a
same-commit control between them of 13 px and this commit measuring 14 px
against its own parent. The scene draws no particles, so this gate is a tripwire
that the world path is undisturbed, not evidence about particles.
Particles remain user-gate debt — the same debt V2c and V4e already carry, to be
paid by casting a spell in a connected session.
Manifest: 6/9 pairs compile. Remaining: mesh (legacy, no consumer), sky (next
commit), terrain_modern.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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