OpenGL 4.5 Buffer Texture : extensions support

Question

I use OpenGL Version 4.5.0, but somehow I can not make texture_buffer_object extensions work for me ("GL_EXT_texture_buffer_object" or "GL_ARB_texture_buffer_object"). I am quite new with OpenGL, but if I understand right, these extensions are quite old and even already included in the core functionality...

I looked for the extensions with "OpenGL Extensions Viewer 4.1", it says they are supported on my computer, glewGetExtension("GL_EXT_texture_buffer_object") and glewGetExtension("GL_ARB_texture_buffer_object") both also return true.

But the data from the buffer does not appear in the texture sample (in the fragment shader the texture contains only zeros).

So, I thought maybe the extensions are somehow disabled by default, and I included enabling these extensions in my fragment shader:

#version 440 core
#extension GL_ARB_texture_buffer_object : enable
#extension GL_EXT_texture_buffer_object : enable

And now I get such warnings at run-time:

***GLSL Linker Log:
Fragment info
-------------
0(3) : warning C7508: extension ARB_texture_buffer_object not supported
0(4) : warning C7508: extension EXT_texture_buffer_object not supported

Please see the code example below:

//#define GL_TEXTURE_BIND_TARGET GL_TEXTURE2D
#define GL_TEXTURE_BIND_TARGET GL_TEXTURE_BUFFER_EXT

.....
    glGenTextures(1, &texObject);
    glBindTexture(GL_TEXTURE_BIND_TARGET, texObject);   

            GLuint bufferObject;
            glGenBuffers(1, &bufferObject);

            // Make this the current UNPACK buffer (OpenGL is state-based)
            glBindBuffer(GL_TEXTURE_BIND_TARGET, bufferObject);
            glBufferData(GL_TEXTURE_BIND_TARGET, nWidth*nHeight*4*sizeof(float), NULL, GL_DYNAMIC_DRAW);
            float *test = (float *)glMapBuffer(GL_TEXTURE_BIND_TARGET, GL_READ_WRITE); 
            for(int i=0; i<nWidth*nHeight*4; i++)
                test[i] = i/(nWidth*nHeight*4.0);
            glUnmapBuffer(GL_TEXTURE_BIND_TARGET); 

            glTexBufferEXT(GL_TEXTURE_BIND_TARGET, GL_RGBA32F_ARB, bufferObject);


    //glTexImage2D(GL_TEXTURE_BIND_TARGET, 0, components, nWidth, nHeight,
    //                0, format, GL_UNSIGNED_BYTE, data);

............

So if I use GL_TEXTURE2D target and load some data array directly to the texture, everything works fine. If I use GL_TEXTURE_BUFFER_EXT target and try to load texture from the buffer, then I get an empty texture in the shader.

Note: I have to load texture data from the buffer because in my real project I generate the data on the CUDA side, and the only way (that I know of) to visualize data from CUDA is using such texture buffers.

So, the questions are : 1) why I become no data in the texture, although the OpenGL version is ok, and Extensions Viewer shows the Extensions as supported ? 2) why trying to enable the extensions in the shader fails ?

Edit details : I updated the post, because I found out the reason for "Invalid Enum" error about that I mentioned first, it was caused by glTexParameteri that is not allowed for buffer textures.

Butterfly Butterfly · Accepted Answer · 2015-05-18T15:43:58

I solved this. I was in a hurry and stupidly missed a very important thing on a wiki page:

https://www.opengl.org/wiki/Buffer_Texture

Access in shaders

In GLSL, buffer textures can only be accessed with the texelFetch function. This function takes pixel offsets into the texture rather than normalized texture coordinates. The sampler types for buffer textures are samplerBuffer.

So in GLSL we should use buffer textures like this:

uniform samplerBuffer myTexture;

void main (void)  
{  
   vec4 color = texelFetch(myTexture, [index]);

not like usual textures:

uniform sampler1D myTexture;

void main (void)  
{  
   vec4 color = texture(myTexture, gl_FragCoord.x);

Warnings about not supported extensions : I think I get them because this functionality is included in the core since OpenGL 3.1, so they should not be enabled additionally any more.

OpenGL 4.5 Buffer Texture : extensions support

1 Answers