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Mirroring rotations

Started by samn Nov 25, 2001 at 11:57 AM 0 replies 950+ views

Original Post

Nov 25, 2001 at 11:57 AM

Does anybody out there know how to mirror a rotation about, say, the YZ plane? My rotations are represented by quaternions (although they could be converted to matrices), so I don''t have access to each individual euler angle, which makes it somewhat more tricky... Cheers, Sam

invective

Nov 26, 2001 at 1:39 AM

If you are using DirectX 8 then I think what you want is D3DXMatrixReflect on your rotation matrix, otherwise, see the documentation for the function for how it constructs the matrix:

  
D3DXMATRIX* D3DXMatrixReflect(
  D3DXMATRIX* pOut,
  CONST D3DXPLANE* pPlane
); 
Builds a matrix that reflects the coordinate system about a plane

This function uses the following formula to compute the returned matrix.

P = normalize(Plane);

-2 * P.a * P.a + 1  -2 * P.b * P.a      -2 * P.c * P.a        0
-2 * P.a * P.b      -2 * P.b * P.b + 1  -2 * P.c * P.b        0
-2 * P.a * P.c      -2 * P.b * P.c      -2 * P.c * P.c + 1    0
-2 * P.a * P.d      -2 * P.b * P.d      -2 * P.c * P.d        1

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