From 6f1971aa9cfe2db01e4a0210115e3e64f5f32a2f Mon Sep 17 00:00:00 2001 From: Erik Date: Sat, 11 Apr 2026 21:18:42 +0200 Subject: [PATCH] =?UTF-8?q?fix(app):=20Phase=209.2=20=E2=80=94=20enable=20?= =?UTF-8?q?back-face=20cull=20in=20translucent=20pass?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The user reported the lifestone crystal (AlphaBlend part 3 of the 4-part 0x020002EE setup) rendered with one side consistently missing — looked like "a box with one side missing, you can see into it" while the whole thing rotated. Isolated via experiment: routing the crystal through the opaque pass (no blending, depth write on) produced a whole solid shape. Routing it through the Phase 9.1 translucent pass (blending on, depth write off) produced the hole. Mesh build was eliminated as the cause. Root cause: our translucent pass matched WorldBuilder's state (SrcAlpha/OneMinusSrcAlpha, DepthMask(false)) but NOT its culling state. WorldBuilder enables GL_CULL_FACE with per-batch CullMode (references/WorldBuilder/Chorizite.OpenGLSDLBackend/Lib/ BaseObjectRenderManager.cs:361-365). Without face culling, the 58 triangles of the closed crystal shell drew in dict-iteration order; back faces that happened to draw AFTER front faces composited over them because depth-write-off meant nothing recorded depth within the translucent set. One face of the crystal ended up permanently overwritten by its own backside. Fix: in pass 2 (translucent) enable GL_CULL_FACE with GL_BACK and CCW front-face winding. Our mesh builder emits pos-side triangles as (0, i, i+1), which is CCW in standard OpenGL conventions, so GL_BACK correctly drops the inward-facing side. Back-face culling is disabled again after pass 2 so subsequent renderers (terrain etc.) see the default state. Known limitation: neg-side polys on translucent surfaces — which my pos/neg mesh-build fix would have emitted with reversed winding — now get culled in the translucent pass. AC rarely uses double-sided polygons on translucent surfaces so this is acceptable, and the opaque pass still renders them correctly. A future Phase 9.3 can track CullMode per sub-mesh and draw double-sided translucents with GL_NONE if it turns out to matter. Also strips the Portal/Lifestone [DIAG] spawn dump that served as one-shot evidence gathering during the investigation. 194 tests green. Co-Authored-By: Claude Opus 4.6 (1M context) --- .../Rendering/StaticMeshRenderer.cs | 25 +++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/src/AcDream.App/Rendering/StaticMeshRenderer.cs b/src/AcDream.App/Rendering/StaticMeshRenderer.cs index 6a2da70..135af25 100644 --- a/src/AcDream.App/Rendering/StaticMeshRenderer.cs +++ b/src/AcDream.App/Rendering/StaticMeshRenderer.cs @@ -135,6 +135,30 @@ public sealed unsafe class StaticMeshRenderer : IDisposable _gl.Enable(EnableCap.Blend); _gl.DepthMask(false); + // Phase 9.2: enable back-face culling for the translucent pass so + // closed-shell translucents (lifestone crystal, glow gems, any + // convex blended mesh) don't draw their back faces over their + // front faces in arbitrary iteration order. Without this, the + // 58 triangles of the lifestone crystal composited with an + // "inside-out" look where the user saw through one face into + // the hollow interior. With back-face culling on, back faces are + // dropped at rasterization time, front faces composite as-is, + // and depth ordering within the front-facing subset is a + // non-issue for closed convex-ish shells. Matches WorldBuilder's + // per-batch CullMode handling in + // references/WorldBuilder/Chorizite.OpenGLSDLBackend/Lib/ + // BaseObjectRenderManager.cs:361-365. + // + // Our fan triangulation emits pos-side polygons as + // (0, i, i+1) which is CCW in standard OpenGL conventions, so + // GL_BACK + CCW front is the correct state. Neg-side polygons + // (if any) use reversed winding and get culled here — that's a + // known limitation and matches the opaque-pass behavior since + // neg-side polys are virtually never translucent in AC content. + _gl.Enable(EnableCap.CullFace); + _gl.CullFace(TriangleFace.Back); + _gl.FrontFace(FrontFaceDirection.Ccw); + foreach (var entity in entityList) { if (entity.MeshRefs.Count == 0) @@ -191,6 +215,7 @@ public sealed unsafe class StaticMeshRenderer : IDisposable // Restore default GL state for subsequent renderers (terrain etc.). _gl.DepthMask(true); _gl.Disable(EnableCap.Blend); + _gl.Disable(EnableCap.CullFace); _gl.BindVertexArray(0); }