selectionBoxAt function

CollisionBox selectionBoxAt(
  1. VoxelQuery q,
  2. int x,
  3. int y,
  4. int z,
)

The box an aimed block's outline is drawn around, in world space: the bounds of what the chunk mesher actually draws in the cell, not the cell. A torch gets a thin post, a slab half a cube, a door a panel, a plant the sheet it grows. Shapes that lean on a neighbour (a wall torch, a ladder) or join one (a fence) read the same neighbours, in the same order, as the mesher does, so the box and the mesh cannot disagree.

Implementation

CollisionBox selectionBoxAt(VoxelQuery q, int x, int y, int z) {
  final table = q.table;
  final shape = table.shapeOf(q.getBlockXYZ(x, y, z));
  bool opaqueAt(int dx, int dz) => table.isOpaque(q.getBlockXYZ(x + dx, y, z + dz));
  // The mesher's per-cell plant jitter is keyed on chunk-local x / z.
  final lx = x % ChunkSize.sizeX, lz = z % ChunkSize.sizeZ;
  final local = switch (shape) {
    BlockShape.cross => _plant(lx, y, lz, 0.28, 0.55 + ((lx + lz) % 3) * 0.1),
    BlockShape.flower => _plant(lx, y, lz, 0.14, 0.62),
    BlockShape.torch => const CollisionBox(0.4, 0, 0.4, 0.6, 0.62, 0.6),
    BlockShape.wallTorch =>
      opaqueAt(-1, 0)
          ? const CollisionBox(0.0, 0.3, 0.4, 0.2, 0.85, 0.6)
          : opaqueAt(1, 0)
          ? const CollisionBox(0.8, 0.3, 0.4, 1.0, 0.85, 0.6)
          : opaqueAt(0, -1)
          ? const CollisionBox(0.4, 0.3, 0.0, 0.6, 0.85, 0.2)
          : const CollisionBox(0.4, 0.3, 0.8, 0.6, 0.85, 1.0),
    BlockShape.panelZ => const CollisionBox(0, 0, 0, 1, 1, _panel),
    BlockShape.panelX => const CollisionBox(0, 0, 0, _panel, 1, 1),
    BlockShape.slab => const CollisionBox(0, 0, 0, 1, 0.5, 1),
    BlockShape.wire ||
    BlockShape.railNs ||
    BlockShape.railEw ||
    BlockShape.railNe ||
    BlockShape.railNw ||
    BlockShape.railSe ||
    BlockShape.railSw => const CollisionBox(0, 0, 0, 1, 0.125, 1),
    BlockShape.railSlopeN ||
    BlockShape.railSlopeE ||
    BlockShape.railSlopeS ||
    BlockShape.railSlopeW => const CollisionBox(0, 0, 0, 1, 0.875, 1),
    BlockShape.fence => _fence(q, x, y, z),
    BlockShape.ladder => ladderBoxAt(q, x, y, z),
    BlockShape.cube ||
    BlockShape.liquid ||
    BlockShape.stairsN ||
    BlockShape.stairsE ||
    BlockShape.stairsS ||
    BlockShape.stairsW => CollisionBox.full,
  };
  return local.shifted(x, y, z);
}