Integer textures

[onesvenus]

Hi, I'm trying to use a 3d integer texture and I'm having some problems while doing a texture lookup in the fragment shader. I'm using OpenGL 3.1 in a GTX280 which supports the GL_EXT_gpu_shader4 extension.

In the call to glTexImage3D I'm using GL_UNSIGNED_INT_8_8_8_8 as the type parameter and GL_RGBA as the internal format.

In the shader I'm using the following call to do the texture lookup:

uvec4 vecColor = texture(3dtext, posFrag.xyz);

Now, I'm assuming that each component of the vecColor variable will be a 32-bit unsigned int where only the lower word has any kind of information. Is it wrong?

The problem is that when I write and load a texture that has all the values set as 0xFF000000 and check if vecColor.r is bigger than 0 (I'm using this comparison ((vecColor.r & 0xFFu) > 0u)), the comparison evaluates to false. In fact, checking any of the components evaluates this comparison to false.

Should I Bit-and each component with 0xFF before comparing or I can assume that the bigger words are 0x00?

A thing I have found while debugging and that may be of some help is that when I load the same texture using GL_UNSIGNED_BYTE and I do a texture lookup in the fragment shader using a sampler2d the results are the expected ones.

Well, if someone can help me I'd be appreciated, I've been looking at the OpenGL specs for hours without finding anything.

Thanks!

 

[Humus]

First of all, you need to use a sized format for internalformat, such as GL_RGBA8. That's true for all textures. For unsigned integer textures you should use GL_RGBA8UI_EXT. For the format parameter you use GL_RGBA_INTEGER_EXT.

http://www.opengl.org/registry/specs/EXT/texture_integer.txt

 

[onesvenus]

Thanks for your reply Humus. It now works.

As I'm using OpenGL 3.1 and integer are now part of the spec I just used GL_RGBA8UI as the internalformat and GL_RGBA_INTEGER as the format parameter. Looking at the Opengl 3.1 reference I can see some tables where RGBA8UI is mentioned but there isn't any kind of explanation.