Multi-Block Rotation

How rotation affects blocks that span multiple grid cells.

Source: index.html lines ~1126–1209

Rotated Dimensions

When a multi-block is rotated, its bounding box dimensions change. A 3×2×1 block rotated 90° around Y becomes 1×2×3.

getRotatedDims(dims, rotIndex)

function getRotatedDims(dims, rotIndex) {
    if (!dims || (dims[0] === 1 && dims[1] === 1 && dims[2] === 1)) return [1, 1, 1];
    const [W, H, D] = dims;
    const r = ROTATIONS_24[rotIndex] || ROTATIONS_24[0];
    const euler = new THREE.Euler(r[0], r[1], r[2]);
    const q = new THREE.Quaternion().setFromEuler(euler);

    // Project each axis through the rotation
    const vx = new THREE.Vector3(W, 0, 0).applyQuaternion(q);
    const vy = new THREE.Vector3(0, H, 0).applyQuaternion(q);
    const vz = new THREE.Vector3(0, 0, D).applyQuaternion(q);

    return [
        Math.round(Math.abs(vx.x) + Math.abs(vy.x) + Math.abs(vz.x)),
        Math.round(Math.abs(vx.y) + Math.abs(vy.y) + Math.abs(vz.y)),
        Math.round(Math.abs(vx.z) + Math.abs(vy.z) + Math.abs(vz.z)),
    ];
}

Uses quaternion rotation to project the original dimension vectors, then sums absolute components to get the axis-aligned bounding box.

Mesh Positioning

computeMultiBlockMeshPos(anchorPos, dims, rotIndex, isEntityGeo, geoBBox)

For rotated multi-blocks, the visual mesh must be positioned so its geometry aligns with the grid:

1. Get geometry bounding box corners
2. Rotate all 8 corners via quaternion
3. Find the minimum corner in world space
4. Position mesh so geometry min aligns with anchor cell min:

   meshPos = anchorPos - (0.5, 0.5, 0.5) - worldMin
   

Occupancy Cells

During prefab loading, multi-blocks occupy multiple cells:

1. Rotated dimensions are calculated
2. For each cell in the rotated bounding box, an invisible occupancy mesh is created
3. All occupancy cells are linked to the anchor block via multiBlockVisual
4. The occupiedCells map prevents duplicate blocks at the same position

Example

A door with multiBlockDim: [1, 2, 1] (1 wide, 2 tall, 1 deep):

• Rotation 0 (Up 0°): occupies (0,0,0) and (0,1,0)
• Rotation 8 (North 0°): rotated dimensions become [1, 1, 2], occupies (0,0,0) and (0,0,1)

Related

• [[Rotation System]] — the 24-rotation lookup table
• [[Coordinate System]] — cell centering and position calculations