erik/acdream
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

fix(scenery): #49 9×9 loop, per-spawn building check, triangle slope

Browse source 
Three fixes to match retail CLandBlock::get_land_scenes (0x00530460):

1. Loop bound: iterate 9×9 vertices (side_vertex_count=9), not 8×8
   cells. Edge vertices (x=8 or y=8) produce valid spawns when the
   per-object displacement shifts the position back into [0, 192).
   Confirmed by named retail decomp do-while condition, WorldBuilder
   vertLength=9, ACViewer Terrain.Count=81, AC2D wTopo[9][9].

2. Building suppression: check at the DISPLACED position's cell
   (CSortCell::has_building per spawn), not at the loop vertex index.
   Matches WorldBuilder buildingsGrid[gx2, gy2] pattern.

3. Slope filter: replace finite-difference gradient approximation
   with triangle-aware normal sampling via new static method
   TerrainSurface.SampleNormalZFromHeightmap. Picks the correct
   triangle via IsSplitSWtoNE, matching retail find_terrain_poly →
   polygon->plane.N.z and WorldBuilder's GetNormal().

Tests: 5 new tests for SampleNormalZFromHeightmap (flat=1.0, sloped<1,
cross-validates with SampleSurface instance method) and DisplaceObject
edge-vertex validity.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Erik 2026-05-07 21:15:11 +02:00
parent 17b4ffde12
commit 833d167ebc
4 changed files with 203 additions and 49 deletions
Download patch file Download diff file Expand all files Collapse all files

67
src/AcDream.Core/Physics/TerrainSurface.cs
View file

@ -198,6 +198,73 @@ public sealed class TerrainSurface
return InterpolateZInTriangle(hBL, hBR, hTR, hTL, tx, ty, splitSWtoNE);
}
/// <summary>
/// Sample the terrain triangle's surface-normal Z component at (localX, localY)
/// from a raw heightmap. Returns the upward component of the unit normal for
/// the specific triangle the point lies in — flat ground returns 1.0, steeper
/// slopes return smaller values. Used by <see cref="SceneryGenerator"/> for
/// the retail slope filter (<c>CLandCell::find_terrain_poly → polygon.plane.N.z</c>).
/// </summary>
public static float SampleNormalZFromHeightmap(
byte[] heights, float[] heightTable,
uint landblockX, uint landblockY,
float localX, float localY)
{
ArgumentNullException.ThrowIfNull(heights);
ArgumentNullException.ThrowIfNull(heightTable);
if (heights.Length < 81)
throw new ArgumentException("heights must have 81 entries", nameof(heights));
if (heightTable.Length < 256)
throw new ArgumentException("heightTable must have 256 entries", nameof(heightTable));
float fx = Math.Clamp(localX / CellSize, 0f, CellsPerSide - 0.001f);
float fy = Math.Clamp(localY / CellSize, 0f, CellsPerSide - 0.001f);
int cx = (int)fx;
int cy = (int)fy;
cx = Math.Clamp(cx, 0, CellsPerSide - 1);
cy = Math.Clamp(cy, 0, CellsPerSide - 1);
float tx = fx - cx;
float ty = fy - cy;
float hBL = heightTable[heights[cx * HeightmapSide + cy ]];
float hBR = heightTable[heights[(cx+1) * HeightmapSide + cy ]];
float hTR = heightTable[heights[(cx+1) * HeightmapSide + (cy+1)]];
float hTL = heightTable[heights[cx * HeightmapSide + (cy+1)]];
bool splitSWtoNE = IsSplitSWtoNE(landblockX, (uint)cx, landblockY, (uint)cy);
float dzdx, dzdy;
if (splitSWtoNE)
{
if (tx > ty)
{
dzdx = (hBR - hBL) / CellSize;
dzdy = (hTR - hBR) / CellSize;
}
else
{
dzdx = (hTR - hTL) / CellSize;
dzdy = (hTL - hBL) / CellSize;
}
}
else
{
if (tx + ty <= 1f)
{
dzdx = (hBR - hBL) / CellSize;
dzdy = (hTL - hBL) / CellSize;
}
else
{
dzdx = (hTR - hTL) / CellSize;
dzdy = (hTR - hBR) / CellSize;
}
}
return 1f / MathF.Sqrt(dzdx * dzdx + dzdy * dzdy + 1f);
}
/// <summary>
/// Pick the cell's triangle for the chosen diagonal and barycentric-
/// interpolate Z. Single source of truth shared by both