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fix(render): close #52 — lifestone visible (alpha-test + cull + uDrawIDOffset)

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Three root causes regressed the Holtburg lifestone since the WB rendering
migration (Phase N.5 retirement amendment, commit dcae2b6, 2026-05-08).
All confirmed via temporary [LIFESTONE-DIAG] instrumentation and visually
verified by the user through the +Acdream test character.

1. **Alpha-test discard** in mesh_modern.frag transparent pass killed
   high-α pixels of dat-flagged transparent surfaces. Native AC
   transparent surfaces routinely include effectively-opaque pixels —
   e.g. the lifestone crystal core (surface 0x080011DE) — that compose
   correctly under (SrcAlpha, 1-SrcAlpha) blending. The original N.5
   §2 rationale ("high-α belongs in opaque pass") doesn't hold for
   surfaces flagged transparent at the dat level: those pixels can't
   reach the opaque pass at all. Fix: remove `α >= 0.95 discard` from
   the transparent pass, keep `α < 0.05 discard` as a fragment-cost
   optimization (skip totally-empty pixels).

2. **Cull state** for the transparent pass was unset by
   WbDrawDispatcher after the N.5 retirement amendment deleted
   StaticMeshRenderer.cs (which had the Phase 9.2 setup at commit
   6f1971a, 2026-04-11). Closed-shell translucents — lifestone crystal,
   glow gems — need GL_CULL_FACE + GL_BACK + GL_CCW in the transparent
   pass; otherwise back faces composite over front faces in iteration
   order under DepthMask(false). Fix: re-establish Phase 9.2's exact
   GL state setup at the top of Phase 8.

3. **uDrawIDOffset uniform** was missing from mesh_modern.vert.
   gl_DrawIDARB resets to 0 at the start of each
   glMultiDrawElementsIndirect call, so the transparent pass — which
   begins later in the indirect buffer — was fetching
   Batches[0..transparentCount) instead of its actual section at
   Batches[opaqueCount..end). The lifestone crystal ended up reading
   the FIRST OPAQUE batch's TextureHandle every frame; as the camera
   moved and the front-to-back opaque sort reordered which group
   landed at BatchData[0], the crystal's apparent texture flickered to
   whatever sat first — typically the player character's body parts.
   Fix: add `uniform int uDrawIDOffset` to the vertex shader, change
   Batches[gl_DrawIDARB] → Batches[uDrawIDOffset + gl_DrawIDARB], and
   set the uniform per-pass in WbDrawDispatcher (0 for opaque,
   _opaqueDrawCount for transparent). Mirrors WorldBuilder's
   BaseObjectRenderManager.cs line 845.

Tests: 1688/1696 passing (8 pre-existing physics/input failures
unchanged). N.5b conformance sentinel 94/94 clean.

Visual: Holtburg lifestone now renders with the spinning blue crystal
correctly composed over the pedestal. Other transparent content (glass,
particle effects, NPC clothing) is unaffected — the same uniform fix
applies globally and is correct for all transparent draws.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-05-10 15:49:05 +02:00
parent c111312e13
commit e40159f4d6
3 changed files with 69 additions and 3 deletions
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20
src/AcDream.App/Rendering/Shaders/mesh_modern.frag
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@ -86,8 +86,24 @@ void main() {
if (uRenderPass == 0) {
if (color.a < 0.05) discard; // opaque pass — kill truly empty only (A2C)
} else {
if (color.a >= 0.95) discard; // transparent pass
if (color.a < 0.05) discard; // skip totally-empty
// Transparent pass.
//
// Phase Post-A.5 (ISSUE #52, 2026-05-10): do NOT discard α≥0.95 here.
// Native AC transparent-flagged surfaces routinely include
// effectively-opaque pixels — e.g. the Holtburg lifestone crystal core
// (surface 0x080011DE) which the spawn manifest classifies as
// transparent (batch.IsTransparent=True) but whose decoded texture
// alpha lands ≥0.95 across the visible surface. Those pixels still
// compose correctly under (SrcAlpha, 1-SrcAlpha) alpha-blending, so
// discarding them here threw away the whole crystal. The original
// N.5 §2 rationale (high-α fragments belong in the opaque pass) does
// not apply when the SURFACE is dat-flagged transparent — those
// pixels can't reach the opaque pass at all.
//
// Keep the α<0.05 short-circuit as a fragment-cost optimization
// (skip fully-empty pixels — saves blend bandwidth on alpha-keyed
// sprites with large transparent margins).
if (color.a < 0.05) discard;
}
vec3 N = normalize(vNormal);