The cellar-ascent grass window was the UNDERSIDE of the z~94 grade
sheet. Retail terrain is single-sided: ACRender::landPolysDraw
(0x006b7040) draws each land triangle ONLY when the camera is on the
POSITIVE (upper) side of its plane (Plane::which_side2 vs
Render::FrameCurrent, zFightTerrainAdjust bias) - a below-grade eye
gets NO terrain, so retail shows sky through the cellar door.
We inherited WB's frame-global cull DISABLE (WB GameScene.cs:841 - an
editor camera goes underground by design) and TerrainModernRenderer.Draw
set no cull state of its own -> terrain rasterized both sides. From a
below-grade eye every aperture sight-ray RISES, so the only 'terrain'
it can see is the grade sheet's underside - which painted the exit-door
aperture (the landscape slice's 2D NDC clip planes (nx,ny,0,dw) have no
depth axis and cannot exclude between-eye-and-portal geometry) and slid
off the door exactly as the eye crossed grade. Membership/viewer was
exonerated by the harness in the previous commit.
Fix: TerrainModernRenderer.Draw owns its cull state (the 7th
self-contained-GL-state instance): Enable(CullFace) + CullFace(Back) +
FrontFace(Ccw), set -> draw -> restore the frame-global CW + cull-off
baseline. GL backface culling evaluates retail's per-triangle eye-side
predicate at rasterization; no shader change.
Pins:
- LandblockMeshTests.Build_AllTriangles_WindCounterClockwiseInWorldXY:
every emitted triangle CCW in world XY across both FSplitNESW split
directions - the winding invariant culling depends on.
- TerrainCullOrientationTests: under the production camera convention
(LookAt up=+Z, Numerics perspective) an up-facing triangle winds CCW
in window space from above (kept) and CW from below (culled) - guards
FrontFace inversion, which would blank terrain from above.
Oracle note: retail's through-portal clip has NO portal-face near plane
(PView::GetClip / Render::set_view install edge planes only); nearer-
than-portal exclusion comes from the eye-side cull + cell-level
admission. No register row: this PORTS the retail mechanism, retiring
an undocumented WB-heritage deviation.
Gate pending: cellar climb (grass window gone) + outdoor sanity glance
(terrain intact from above).
Suites: App 263+1skip / Core 1443+2skip / UI 420 / Net 294.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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