The visual-win commit that wires up the Phase 3c.1/.2/.3 building blocks:
Holtburg's terrain now uses AC's real per-cell texture-merge blend
(base + up to 3 terrain overlays + up to 2 road overlays, with alpha
masks from the alpha atlas) instead of the flat per-vertex single-layer
atlas lookup that preceded it.
Geometry rewrite:
- New TerrainVertex struct (40 bytes): Position(vec3) + Normal(vec3) +
Data0..3 (4x uint32 packed blend recipe)
- LandblockMesh.Build is now cell-based: iterates 8x8 cells instead of
the old 9x9 vertex grid, emits 6 vertices per cell (two triangles),
384 total vertices per landblock
- For each cell: extract 4-corner terrain/road values → GetPalCode →
BuildSurface (cached across landblocks via a shared surfaceCache) →
FillCellData → split direction from CalculateSplitDirection → emit
6 vertices in the exact gl_VertexID % 6 order WorldBuilder's vertex
shader expects
- Per-vertex normals preserved via Phase 3b central-difference
precomputation on the 9x9 heightmap, interpolated smoothly across
the cell (we deliberately didn't adopt WorldBuilder's dFdx/dFdy
flat-shade approach — Phase 3a/3b user-tuned lighting was worth
keeping)
Renderer rewrite:
- TerrainRenderer VAO: vec3 Position, vec3 Normal, 4x uvec4 byte
attributes for Data0..3. The uvec4-of-bytes read pattern matches
Landscape.vert so the ported shader math stays byte-for-byte
identical to WorldBuilder's.
- Binds both atlases: terrain atlas on unit 0 (uTerrain), alpha atlas
on unit 1 (uAlpha)
Shader rewrite (ports of WorldBuilder Landscape.vert/.frag, trimmed):
- terrain.vert: unpacks the 4 data bytes + rotation bits, derives the
cell corner from gl_VertexID % 6 + splitDir, rotates the cell-local
UV per overlay's rotation field, and computes world-space normal
for the fragment shader
- terrain.frag: maskBlend3 three-layer alpha-weighted composite for
terrain overlays, inverted-alpha road combine, final composite
base * (1-ovlA)*(1-rdA) + ovl * ovlA*(1-rdA) + road * rdA. Phase
3a/3b directional lighting applied on top (SUN_DIR, AMBIENT=0.25,
DIFFUSE=0.75, in sync with mesh.frag).
- Editor uniforms (grid, brush, unwalkable slopes) deliberately
omitted — not applicable to a game client
- Per-texture tiling factor hardcoded to 1.0 for now (WorldBuilder
reads it from uTexTiling[36] uploaded from the dats); one tile per
cell = 8 tiles per landblock-side, slightly coarser than the old
~2x-per-cell tiling. Tunable via the TILE constant if needed.
TerrainAtlas grew parallel TCode/RCode lists (CornerAlphaTCodes,
SideAlphaTCodes, RoadAlphaRCodes) so TerrainBlendingContext can be
built without the mesh loader touching the dats directly.
GameWindow builds a TerrainBlendingContext once, shares a Dictionary
<uint, SurfaceInfo> surfaceCache across all 9 landblocks. Output:
"terrain: 137 unique palette codes across 9 landblocks" — avg ~15
unique per landblock, cache reuse healthy.
LandblockMeshTests rewritten for 384-vertex layout. 77/77 tests green.
Visual smoke run launches clean: no shader compile/link errors, no
GL warnings, terrain renders to the screen.
User visual verification is the final acceptance gate for Phase 3c.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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