No expert here (heck, I've done maybe 5 minutes of OpenGL so far).
It reads like they use a special pixel shader to color each pixel of a texture in a more of less unique color based on when the pixel (or maybe block) was scheduled to be shaded (I'm guessing here based on the atomic counter bit). This yields a texture that shows the order in which pixel shaders are run on a texture. This seems to be different for different GPUs and architectures (unsurprisingly) and also seems to give insights into how certain things are implemented.
But that's all just a bit of guessing. Someone else might be able to give an actual explanation.
Yea well reading it closely, the red's value is what you see with the highest frequency of change. You can see that red increases then increments green, then starts over again at zero, so by looking closely at red, you can see where the computations stop and start over again, thus giving you the reds pattern. As to what it means, who knows.
It reads like they use a special pixel shader to color each pixel of a texture in a more of less unique color based on when the pixel (or maybe block) was scheduled to be shaded (I'm guessing here based on the atomic counter bit). This yields a texture that shows the order in which pixel shaders are run on a texture. This seems to be different for different GPUs and architectures (unsurprisingly) and also seems to give insights into how certain things are implemented.
But that's all just a bit of guessing. Someone else might be able to give an actual explanation.