[C4D] Get vertex normal

c4d-get-vertex-normal.cpp

/// Return the normal vector for a vertex of a polygon object.
/// The normal is computed as an average of the normals of all polygons that are neighbors to the specified vertex.
///
/// @param[in] op The PolygonObject
/// @param[in] neighbor Pointer to a Neighbor object. Must already be initialized, caller owns the pointed object.
/// @param[in] pointIndex The index of the vertex we want the normal of
/// @return The normal of the point in local object space
static Vector GetVertexNormal(PolygonObject *op, Neighbor *neighbor, Int32 pointIndex)
{
	// Variables
	CPolygon *pNeighborPoly = nullptr;
	Int32 *neighborFaceArr = nullptr;
	Int32 neighborFaceCount = 0;
	CPolygon *polygonArr = op->GetPolygonW();
	Vector *pointArr = op->GetPointW();
	Vector resultNormal;
	
	// Get polygons attached to point
	neighbor->GetPointPolys(pointIndex, &neighborFaceArr, &neighborFaceCount);
	if (neighborFaceCount < 1)
		return resultNormal;
	
  // Iterate the neighboring polygons and compute their face normals
	for (Int32 faceIndex = 0; faceIndex < neighborFaceCount; ++faceIndex)
	{
    // Get polygon
		pNeighborPoly = &polygonArr[neighborFaceArr[faceIndex]];
		
		// Compute two vectors along polygon's vertices
		Vector v1 = pointArr[pNeighborPoly->b] - pointArr[pNeighborPoly->a];
		Vector v2 = pointArr[pNeighborPoly->c] - pointArr[pNeighborPoly->a];
		
		// Get cross-product: That's the face normal
    // Add it to the result normal
		resultNormal += Cross(v1, v2);
	}
  // Devide resultNormal by number of neighboring polygons.
  // This will get us an average normal of all the normals of the neighboring polygons.
	resultNormal /= neighborFaceCount;
	
	// Return resulting normalized normal
	return resultNormal.GetNormalized();
}