Adds the GPU mechanism to clip drawing to a per-cell screen-space convex
region via gl_ClipDistance, consumed by the mesh + terrain vertex shaders.
This is the MECHANISM only — every instance defaults to slot 0 (no-clip /
pass-all) and terrain to count 0, so the running game renders IDENTICALLY to
pre-U.3 (verified: offline launch compiles both shaders and reaches steady
state; no GL errors). U.4 populates real clip data from portal visibility.
Binding contract (define once, both sides obey):
- mesh_modern.vert: SSBO binding=2 CellClip[] (shared per-frame regions, slot 0
reserved no-clip) + SSBO binding=3 uint[] per-instance slot, indexed by the
IDENTICAL gl_BaseInstanceARB+gl_InstanceID used for binding=0. binding=0/1
untouched.
- terrain_modern.vert: UBO binding=2 TerrainClip { int count; vec4 planes[8]; }
for the single OutsideView region (UBO namespace; SceneLighting is UBO
binding=1, so binding=2 is free and does not collide with the mesh SSBO
binding=2). count 0 = ungated.
- Both redeclare out gl_PerVertex { vec4 gl_Position; float gl_ClipDistance[8]; }
and set unused planes (i >= count) to +1.0 so they pass everything.
CellClip std430 layout (144 bytes/slot): count@0, 3 pad uints@4/8/12,
planes[8]@16 (vec4 stride 16). Terrain UBO std140: count@0 (padded to 16),
planes[8]@16 → 144 bytes. Verified by ClipFrameLayoutTests (8 new tests).
Pieces:
- ClipFrame: per-frame container + uploader for the SHARED clip data (binding=2
SSBO + terrain UBO). NoClip() = slot 0 + terrain count 0. AppendSlot /
SetTerrainClip pack std430/std140 bytes for U.4. UploadShared binds both.
- WbDrawDispatcher + EnvCellRenderer: each owns its binding=3 zero buffer
(all-zeros sized to its instance count → slot 0), re-binds binding=2 from the
shared ClipFrame id (or an internal no-clip fallback if unwired) before MDI.
gl_ClipDistance is per-vertex, so the single glMultiDrawElementsIndirect per
group is preserved — no draw splitting.
- TerrainModernRenderer: binds the terrain clip UBO (shared or no-clip fallback)
before its draw.
- GameWindow: glEnable(GL_CLIP_DISTANCE0..7) once at init (unused planes pass-all
so always-on avoids per-draw thrash); per frame builds ClipFrame.NoClip(),
UploadShared, and hands the buffer ids to the three renderers (tiny diff; U.4
swaps NoClip() for the real portal-visibility frame).
Gate: dotnet build green; App suite 134/134; offline launch confirms both
shaders compile + link with no GL errors.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Subtract 0.01 from every terrain vertex Z in the modern terrain vertex
shader, matching retail's per-draw nudge applied inside
ACRender::landPolysDraw(arg2=2). Coplanar building floors now always win
the depth test against the rendered terrain, so the visual "ground at
the building floor" reads as the building's floor, not as Z-fighting.
Constant 0.01f bit-equals retail's float literal 0.00999999978 when
rounded to single precision.
Render-only — physics reads the un-nudged heightmap via
TerrainSurface.SampleZ / SampleZFromHeightmap. The same render-vs-
physics split is already established for EnvCell render lift
(+0.02m at GameWindow.cs around the cell-mesh draw).
Retail anchors:
docs/research/named-retail/acclient_2013_pseudo_c.txt:1120769
docs/research/named-retail/acclient_2013_pseudo_c.txt:702254
Cross-ref:
docs/research/2026-05-25-issue-100-terrain-cutout-handoff.md
docs/superpowers/plans/2026-05-25-issue-100-terrain-cutout.md
Followed by Task 2 (delete the hiddenTerrainCells / BuildingTerrainCells
plumbing). Visible result of this commit alone: building floors stop
Z-fighting, but the 24m x 24m transparent rectangles persist until the
plumbing is removed.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Deletes:
- TerrainChunkRenderer.cs (454 lines, replaced by TerrainModernRenderer)
- TerrainRenderer.cs (247 lines, older sibling, no production users)
- terrain.vert / terrain.frag (replaced by terrain_modern.{vert,frag})
Removes the temporary Task 8 perf-benchmark toggle (ACDREAM_LEGACY_TERRAIN
env var, _useLegacyTerrain field, parallel _terrainLegacy renderer
instance, [TERRAIN-DIAG/modern|legacy] label suffix). The modern path
is now the only path. Mirror N.5's mandatory-modern amendment: missing
GL_ARB_bindless_texture throws NotSupportedException at startup
(already in place via the BindlessSupport.TryCreate gate).
Three load-bearing research comments preserved verbatim from terrain.vert
into terrain_modern.vert before deletion: the MIN_FACTOR = 0.0 N-dot-L
floor block (cross-ref Lambert brightness split), the aPacked3 bit
layout, the gl_VertexID corner-table 2026-04-21 ConstructPolygons fix.
Also retires the now-orphaned _shader field (legacy terrain pipeline
was its only user).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Vertex shader for the modern terrain dispatcher. Bit-identical math
to today's terrain.vert (Phase 3c per-cell mesh + Phase G AdjustPlanes
lighting). The only structural change is the version + bindless
extension preamble — sampler access stays a regular sampler2DArray
uniform; bindless-ness is invisible at the GLSL level.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
