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enter image description here

The image above is a static capture of a dynamic OpenGL project I created in which I wrapped a NASA albedo, i.e., sans clouds, image on an OpenGL generated sphere. In so doing, I also generated the UV coordinates associated with each vertex position.

This was an incremental learning effort in which I had already applied model matrix corrections to the vertex positions for the rotating and translating (orbiting) "Earth".

I was surprised to find that I did not have to apply a model matrix correction to the UV coordinates.

I have tentatively concluded that once the jpg image coordinates are associated with the corresponding vertex positions with the UV coordinates in the range of [0, 1], they are fixed and need no further correction.

Does that sound correct, or is there more to the situation?

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That is correct: the texture coordinates for a model don’t need to change as you move that model around a scene or manipulate it. They are mapping parts of the geometry surface to parts of an image and thus stay fixed.

You may need to update texture coordinates if you want to do some kind of animation of the texture across a surface (although there are still other ways to do that) or similar more complex effect. But in general, you don't.

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  • \$\begingroup\$ Thank you, Josh. I have only been learning OpenGL for a little while and the terminology is enough to drive one to drink! Texture coordinates, uv-coordinates, on and on and little in the way of consistent documentation. It seems that the more complicated the topics get, the less reliable is the documentation. \$\endgroup\$ – user34299 Aug 3 '19 at 13:42
  • \$\begingroup\$ There are lots of terms that mean the same thing because they originate from slightly different places. You may also here "st coordinates" instead of "uv coordinates," for example. It's a fact of life, I'm afraid. \$\endgroup\$ – user1430 Aug 3 '19 at 13:46

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