Question

I intend to make Graphics calculation with OpenCL such as ray casting, ray marching and others. And I want to use OpenGL to display result of this calculations (pixel images). I use texture buffer attached to frame buffer. OpenCL writes the result into the texture and then I use glBlitFrameBuffer function to copy texture data to application window framebuffer.
I met a CL/GL inter problem during the implementation of it. I wrote a simple example to show it. This example shows framebuffer object and texture object initialization, their conjunction, OpenCL buffer creation from GL texture buffer. At the end the main render loop is shown. It consists of texture writing with new data in each frame, framebuffer attachment and copying of this framebuffer.

Texture Initialization:

for (int i = 0; i < data.Length; i +=4) {
    data [i] = 255;
}
GL.BindTexture (TextureTarget.Texture2D, tboID [0]);
GL.TexImage2D<byte>(TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba8, w, h, 0,
                    PixelFormat.Rgba, PixelType.UnsignedByte, data);
GL.BindTexture (TextureTarget.Texture2D, 0)

TBO+FBO Initialization:

 GL.BindFramebuffer (FramebufferTarget.FramebufferExt, fboID [0]);
 GL.FramebufferTexture2D (FramebufferTarget.FramebufferExt, FramebufferAttachment.ColorAttachment0,
                          TextureTarget.Texture2D, tboID [0], 0);
 GL.BindFramebuffer (FramebufferTarget.FramebufferExt, 0);

CL/GL Initialization:

bufferID = CL.CreateFromGLTexture2D (context, memInfo, textureTarget, mipLevel, glBufferObject, out errorCode);

Render Loop:

 for (int i = 0; i < data.Length; i += 4) {
     data [i] = tt;
 }
 tt++;
 GL.BindTexture (TextureTarget.Texture2D, tboID [0]);
 GL.TexImage2D<byte> (TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba8, w, h, 0,
                      PixelFormat.Rgba, PixelType.UnsignedByte, data);

 GL.BindTexture (TextureTarget.Texture2D, 0);
 GL.BindFramebuffer (FramebufferTarget.FramebufferExt, fboID [0]);
 GL.FramebufferTexture2D (FramebufferTarget.FramebufferExt, FramebufferAttachment.ColorAttachment0,
                          TextureTarget.Texture2D, tboID [0], 0);
 GL.BindFramebuffer (FramebufferTarget.FramebufferExt, 0);GL.BindFramebuffer (FramebufferTarget.ReadFramebuffer, fboID [0]);

 GL.ReadBuffer (ReadBufferMode.ColorAttachment0);
 GL.DrawBuffer (DrawBufferMode.Back);

 GL.BlitFramebuffer (0, 0, w, h, 0, 0, w, h, ClearBufferMask.ColorBufferBit, BlitFramebufferFilter.Nearest);

 GL.BindFramebuffer (FramebufferTarget.ReadFramebuffer, 0);

At the first glance this code looks weird, but it completely shows my problem. CL does not work at all here. In this application OpenCL context is created and OpenCL buffer initialization is occured.
The work of this should be simple. The color of screen is being changed from black to red. And It does not work in this way. The color does not change from the initial red (texture initialization).
But it works normal when I comment the CL/GL Initialization (creation of CL buffer from GL texture).
Why is it so? Why the behavior of the GL buffer is changed depending on CL attachments? How to fix it and make it works?

Answer 1

Finally we were able to run Itun’ code on my system (Windows 7 / AMD Radeon HD 5870). Recall that Itun’ code gradually changes color in texture from black to red by means of GL after activating GL/CL Interop on this texture.

The results are at least strange. On my system it works as intended. However, on Itun’ system (Windows 7 / NVidia GeForce) the same code does not work at all and does not provide any exceptions or error codes. In addition, I would like to mention that CL works with this texture properly on both systems. Therefore, something is wrong with GL in this case.

We have no idea on what’s going on – it could be either Itun’ outdated GPU hardware or buggy NVidia drivers.