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fix(core): ACME cross-check fixes — normals, placement, scenery

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Four fixes from the ACME StaticObjectManager cross-reference:

1. GfxObjMesh: normalize vertex normals (1d). Dat normals may not be
   unit-length; without normalization, lighting is wrong per-vertex.

2. SetupMesh: add third-fallback placement frame (2a). If neither
   Resting nor Default exists, use the first available frame from
   PlacementFrames. Matches ACME's GetDefaultPlacementFrame.

3. SceneryGenerator: building cell exclusion (4d). Compute which
   terrain vertices have buildings (from LandBlockInfo.Objects +
   Buildings), skip scenery spawns in those cells. Prevents trees
   from spawning inside building footprints.

4. SceneryGenerator: slope filter (4e). Compute terrain normal Z at
   each displaced position and check against ObjectDesc.MinSlope /
   MaxSlope bounds. Prevents trees from spawning on cliff faces.

Also confirmed 4f (scenery Z=0) is NOT a bug — GameWindow's hydrator
lifts scenery to terrain Z at line 1213. The Z=0 in SceneryGenerator
is a placeholder correctly overridden at render time.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-04-12 22:52:08 +02:00
parent 05749f52e0
commit 9d4967a461
4 changed files with 61 additions and 7 deletions
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31
src/AcDream.Core/World/SceneryGenerator.cs
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@ -46,7 +46,9 @@ public static class SceneryGenerator
DatCollection dats,
Region region,
LandBlock block,
uint landblockId)
uint landblockId,
HashSet<int>? buildingCells = null,
float[]? heightTable = null)
{
var result = new List<ScenerySpawn>();
@ -74,6 +76,10 @@ public static class SceneryGenerator
// check in get_land_scenes(). Roads should not have trees/rocks.
if (IsRoadVertex(raw)) continue;
// Skip cells that contain buildings (ACME conformance fix 4d).
// Building footprints shouldn't have scenery spawning inside them.
if (buildingCells is not null && buildingCells.Contains(i)) continue;
if (terrainType >= region.TerrainInfo.TerrainTypes.Count) continue;
var sceneTypeList = region.TerrainInfo.TerrainTypes[(int)terrainType].SceneTypes;
if (sceneType >= sceneTypeList.Count) continue;
@ -133,10 +139,25 @@ public static class SceneryGenerator
if (IsRoadVertex(nearRaw)) continue;
}
// Z at the cell corner from the heightmap. Skipping slope-based
// Z placement (ACViewer uses find_terrain_poly which we don't have)
// — accept that some scenery will float or clip.
float lz = 0f; // will be lifted to ground at render time via landblock heightmap
// Slope filter (ACME conformance fix 4e): compute terrain normal
// Z-component at the displaced position and check against the
// object's MinSlope/MaxSlope bounds.
if (heightTable is not null && (obj.MinSlope > 0f || obj.MaxSlope < 1f))
{
int sx = Math.Clamp((int)(lx / CellSize), 0, VerticesPerSide - 2);
int sy = Math.Clamp((int)(ly / CellSize), 0, VerticesPerSide - 2);
int sxR = sx + 1;
int syU = sy + 1;
float h00 = heightTable[block.Height[sx * VerticesPerSide + sy]];
float h10 = heightTable[block.Height[sxR * VerticesPerSide + sy]];
float h01 = heightTable[block.Height[sx * VerticesPerSide + syU]];
float dx = (h10 - h00) / CellSize;
float dy = (h01 - h00) / CellSize;
float nz = 1f / MathF.Sqrt(dx * dx + dy * dy + 1f); // normal Z component
if (nz < obj.MinSlope || nz > obj.MaxSlope) continue;
}
float lz = 0f; // lifted to ground at render time via landblock heightmap
// Rotation
Quaternion rotation = Quaternion.Identity;