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I am importing my code from OpenGL to Direct3D. My D3DTS_PROJECTION uses D3DXMatrixPerspectiveFovRH, and my D3DTS_VIEW uses D3DXMatrixLookAtRH to set a view equal to OpenGL's view. My question is why do I have to switch all of my 1.0000 Tex(v) texture coordinates to "minus value" in D3D to get equal texture mapping as in OpenGL.

OpenGL:

//T(u) T(v) 1.0000, 1.0000, 0.0000, 1.0000, 1.0000, 0.0000, 1.0000, 0.0000, 0.0000, 1.0000, 0.0000, 0.0000, 0.0000, 1.0000, 0.0000, 0.0000, 1.0000, 1.0000, 1.0000, 1.0000, 0.0000, 0.0000, 1.0000, 0.0000, // ...

Direct3D:

// T(u) T(v) D3DXVECTOR2( 1.0000f, -1.0000f) D3DXVECTOR2( 0.0000f, -1.0000f) D3DXVECTOR2( 1.0000f, 0.0000f) D3DXVECTOR2( 1.0000f, 0.0000f) D3DXVECTOR2( 0.0000f, -1.0000f) D3DXVECTOR2( 0.0000f, 0.0000f) D3DXVECTOR2( 0.0000f, -1.0000f) D3DXVECTOR2( 0.0000f, 0.0000f) D3DXVECTOR2( 1.0000f, -1.0000f) D3DXVECTOR2( 1.0000f, -1.0000f) D3DXVECTOR2( 0.0000f, 0.0000f) D3DXVECTOR2( 1.0000f, 0.0000f) // ...

Is it because Direct3D's origin (0.0) of texture coordinates lies in different place than in OpenGL?

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1 Answer 1

Reset to default
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For texture spaces, in Direct3D (0, 0) is top-left, in OpenGL (0, 0) is bottom-left. Therefore the v-coordinate will be upside down in one of these APIs.

However, I wouldn't recommend negating the v-coordinate as this will only work if you're using a sampler with wrapping.

You can fix the v-coordinate as follows:

v = 1.0f - v;
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  • \$\begingroup\$ And also negating them will create inaccurate results if you are going to do any sort of transformation with the uv´s. or create some sort of data from it. \$\endgroup\$ Commented Apr 7, 2014 at 12:06
  • \$\begingroup\$ Thank you for your answer! This is just what I needed. No more "minus values" in texture coordinates and the final effect is equal to OpenGL's. \$\endgroup\$ Commented Apr 7, 2014 at 17:05

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