Question

Sorry for a really noob-level question…

I want to apply a specific piece of the texture (not the entire texture) to a quad. The texture is a 256×64 image and I’d like to be able to specify the relevant piece by stating the pixel coordinates of its upper-left and bottom-right corners ( [0,0] being the upper left corner of the whole image and [256,64] being the bottom right).

Any ideas on how to do that?

Thanks.

Answer 1

The fractional answer is correct, but if you want to use integer texture coordinates (for example in a VBO) you can use the GL_TEXTURE matrix to change your texture coordinate system:

        glMatrixMode(GL_TEXTURE)
        glLoadIdentity()
        glScalef(1f/256f, 1f/64f, 1f)

After that your texture coordinate units would be pixels. Another scaling strategy would be to scale so each tile is 1×1 in the final units.