Difference between glTexSubImage and glTexImage function in OpenGL

开发者_运维百科

What is the difference between the two functions? Any performance difference?

Thanks..

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You create a texture using glTexImage, and then update its contents with glTexSubImage. When you update the texture, you can update the entire texture, or just a sub-rectangle of it.

It is far more efficient to create the one texture and update it than to create it and delete it repeatedly, so in that sense if you have a texture you want to update, always use glTexSubImage (after the initial creation).

Other techniques may be applicable for texture updates. For example, see this article on texture streaming for further information.

(Originally, this post suggested using glMapBuffer for texture updates - see discussion below.)

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The gl functions with "sub" in the name aren't limited to power-of-2 dimensions. As gavinb points out, you need to use the non-sub variant once to set the overall dimensions, but I don't agree that calling the non-sub variant repeatedly is any slower than using "sub" for updates -- the GPU is still free to overwrite the existing texture in place as long as you are using the same texture id.