Ports WorldBuilder's full BuildTexture / FillCellData pipeline as
pure CPU functions in TerrainBlending.cs, along with the SurfaceInfo
recipe record and a TerrainBlendingContext input struct that carries
the atlas index lists the algorithm needs.
This is still pure algorithm work — no GL, no shaders, no mesh gen
changes. Visual Phase 3c.4 next commit wires it into LandblockMesh
and rewrites the terrain shaders to consume Data0..3.
Added (all ports of WorldBuilder LandSurfaceManager methods):
- ExtractTerrainCodes: inverse of GetPalCode terrain bits
- PseudoRandomIndex: deterministic hash over palette code for alpha
variant selection; overflow-dependent int math matches WorldBuilder
byte-for-byte
- RotateTerrainCode: *2 with wrap (1→2→4→8→1, multi-corner patterns
handled in tests)
- GetRoadCodes: decodes the 8-bit road mask into up to two canonical
road patterns + allRoad flag; magic 0xE/0xD/0xB/0x7 switch kept verbatim
- FindTerrainAlpha: picks corner vs side alpha map, walks the 4
rotations looking for a TCode match, returns (alphaLayer, rotation)
or (255, 0) for "not found"
- FindRoadAlpha: same idea for road maps, iterates all maps from a
pseudo-random offset
- BuildSurface: composes the above into a SurfaceInfo, handling the
all-road, all-duplicate-terrain, and distinct-terrain cases via
BuildOverlayLayers + BuildWithDuplicates (ports GetTerrainTextures +
BuildTerrainCodesWithDuplicates)
- FillCellData: packs a SurfaceInfo + CellSplitDirection into the 4
uint32 vertex attributes Data0..Data3. Byte layout documented in
XML comment and matches WorldBuilder's Landscape.vert uvec4 byte
unpacking exactly.
SurfaceInfo record carries resolved atlas byte layers directly (base +
3 terrain overlays + 2 road overlays, each with optional alpha layer
and 0-3 rotation). Sentinel 255 = "slot unused".
Tests (14 new, 75/75 total):
- ExtractTerrainCodes round-trip with GetPalCode
- RotateTerrainCode single-corner cycle + multi-corner patterns
- GetRoadCodes: no-road, all-road, single-corner road
- PseudoRandomIndex: range, count=0 guard, determinism
- BuildSurface: all-grass → base only; all-road → road as base;
two-grass-two-dirt → base + overlay
- FillCellData: full round-trip bit layout with recognizable
byte values in every slot, plus a no-road1 case that verifies
the texRd1 slot collapses to 255 when road1 alpha is absent
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
First of four steps porting WorldBuilder's texture-merge terrain
blending. This commit is pure CPU math with no GL or dat dependencies
so the ported logic can be verified in isolation before it starts
driving real rendering.
Ported:
- GetPalCode(r1..r4, t1..t4): packs corner terrain/road bits into
a 32-bit palette code (bit layout documented in XML comment)
- CalculateSplitDirection: deterministic hash picking SWtoNE vs
SEtoNW triangulation for a cell; magic constants kept exact to
match AC's server-side collision triangulation
- CellSplitDirection enum with values matching WorldBuilder's so
later bit-packing stays byte-identical
Tests (10 new, 58/58 passing total):
- GetPalCode golden value for all-grass-no-roads: 0x10008421
(hand-computed from the bit layout, not derived from a run)
- GetPalCode all-zero produces only the sizeBits marker
- GetPalCode determinism, road-flag isolation (r1 flip touches
only bit 26), size bit always set, terrain region bounded to
bits 0-19
- CalculateSplitDirection hand-computed golden for (0,0,0,0):
(1813693831 - 1369149221) * (1/2^32) ~= 0.1035 < 0.5 -> SWtoNE
- Determinism
- Across a full 8x8 landblock the hash produces a mix of both
split directions (would fail if the hash collapses)
Deferred to Phase 3c.3 (need dat data for TexMerge):
BuildSurface, FillCellData, PseudoRandomIndex, SurfaceInfo
Reference: WorldBuilder Chorizite.OpenGLSDLBackend/Lib/LandSurfaceManager.cs
WorldBuilder.Shared/Modules/Landscape/Lib/TerrainUtils.cs
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
