CODEWITHSUNDEEP
opengltextures
jiandingzhe
jiandingzhe

Reputation: 2121

How to set all pixels of a texture to one value?

I'm using texture in grids: firstly a large texture (such as 1024x1024 or 2048x2048) is created without data, then areas being used are set with glTexSubImage2d calls. However, I want to have all pixels to have initial value of 0xffff, not zero. And I feel it's stupid to allocate megabytes of all-0xffff host memory only for initialize texture value. So is it possible to set all pixels of a texture to a specific value, with just a few calls?

Specifically, is it possible in OpenGL 2.1?

Upvotes: 3

Views: 451

Answers (1)

Yakov Galka
Yakov Galka

Reputation: 72449

There is glClearTexImage, but it was introduced in OpenGL 4.4; see if it's available to you with the ARB_clear_texture extension.

If you're absolutely restricted to the core OpenGL 2.1, allocating client memory and issuing a glTexImage2D call is the only way of doing that. In particular you cannot even render to a texture with unextended OpenGL 2.1, so tricks like binding the texture to a framebuffer (OpenGL 3.0+) and calling glClearColor aren't applicable. However, a one-time allocation and initialization of a 1-16MB texture isn't that big of a problem, even if it feels 'stupid'.

Also note that a newly created texture image is undetermined; you cannot rely on it being all zeros, thus you have to initialize it one way or another.

Upvotes: 4

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