Rotation matrix from OpenGL to DirectX

Question

I have an application which uses openGL and i have to port it to DirectX. To sum up my issue : How can I port rotation matrix based on a right-handed coordinate system to a left-handed coordinate system ? I hardly found some documentation on the internet.

This is what i found on MSDN:

• Flip the order of triangle vertices so that the system traverses them clockwise from the front. In other words, if the vertices are v0, v1, v2, pass them to Direct3D as v0, v2, v1.

• Use the view matrix to scale world space by -1 in the z-direction. To do this, flip the sign of the _31, _32, _33, and _34 member of the D3DMATRIX structure that you use for your view matrix.

This is work fine except i can not flip easily my vertices because i got an 3D model from CATIA which is not a primitive, so i can't use it.

(I'm aware of row-major and column-major difference, it does not matter)

Do you know how i can port my rotation matrix from openGL to DirectX ?

Thanks a lot

Answer 1

I believe, the only difference (besides row/column majorness) is that DirectX uses lefthanded coordinate system and openGL uses righthanded system. You simply need to flip one base vector. Rotation matrix (r) is just a definition of those vectors. So making

r._31 = -r._31;
r._32 = -r._32;
r._33 = -r._33;
r._34 = -r._34;

will just flip the z-coordinates.

The other problem is the triangle ordering (and Front/Back face culling). If you can turn backface-culling off (or switch to frontface-culling), you are OK.