spec(N.5b): design for terrain on the modern rendering path
Brainstormed 2026-05-09. Lifts outdoor terrain rendering onto N.5's
modern primitives (bindless textures + glMultiDrawElementsIndirect)
preserving the visible terrain pixel-for-pixel and preserving
physics-vs-visual Z agreement (issue #51).
Key decisions:
- Path C: WB renderer pattern + acdream's existing LandblockMesh.Build
(which uses retail's FSplitNESW formula, verified at retail addr
00531d10). Path A killed by 49.98% measured divergence vs retail.
- Single global VBO/EBO + slot allocator (one slot per landblock),
uint32 indices with baseVertex baked, mirror WB's pattern.
- Keep TerrainAtlas (palCode-based fragment blending), add bindless
handles. No LandSurfaceManager adoption.
- Separate terrain_modern.vert/.frag (port of today's terrain.vert/.frag
with bindless preamble; same blend math, same AdjustPlanes lighting).
- Pure-CPU Z-conformance sentinel: meshTriZ vs TerrainSurface within
1mm across 10 representative landblocks x 100 sample points.
- Acceptance: build green, conformance test passes, ~6-8 GL calls/frame
for terrain regardless of scene size, [TERRAIN-DIAG] cpu_ms at
radius=5 >=10% lower than today's per-LB-binds path.
Files added: TerrainModernRenderer + TerrainSlotAllocator +
terrain_modern.vert/.frag + 2 test files.
Files deleted: TerrainChunkRenderer + TerrainRenderer +
terrain.vert/.frag.
Out of scope: EnvCells/dungeons, sky, particles, A.5 LOD,
LandSurfaceManager adoption, fork-patching WB.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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