//-----------------------------------------------------------------------------
// Transform a plane
//-----------------------------------------------------------------------------
void MatrixTransformPlane( const VMatrix &src, const cplane_t &inPlane, cplane_t &outPlane )
{
// What we want to do is the following:
// 1) transform the normal into the new space.
// 2) Determine a point on the old plane given by plane dist * plane normal
// 3) Transform that point into the new space
// 4) Plane dist = DotProduct( new normal, new point )
// An optimized version, which works if the plane is orthogonal.
// 1) Transform the normal into the new space
// 2) Realize that transforming the old plane point into the new space
// is given by [ d * n'x + Tx, d * n'y + Ty, d * n'z + Tz ]
// where d = old plane dist, n' = transformed normal, Tn = translational component of transform
// 3) Compute the new plane dist using the dot product of the normal result of #2
// For a correct result, this should be an inverse-transpose matrix
// but that only matters if there are nonuniform scale or skew factors in this matrix.
Vector3DMultiply( src, inPlane.normal, outPlane.normal );
outPlane.dist = inPlane.dist * DotProduct( outPlane.normal, outPlane.normal );
outPlane.dist += DotProduct( outPlane.normal, src.GetTranslation() );
}
