EXT_histogram -> ARB_imaging subset
I would like to try it out to measure how much texels are being rendered.
However, looks like it works only for {Copy,Draw,Read}Pixels and this is bad.
I remember of a nVidia whitepaper in which they said there’s a way to count how much pixels passed thuru the pipe. Does anyone knows something about it? Maybe they were referring only to {Copy,Draw,Read} operations?
On any hardware you can count pixels by either incrementing the stencil buffer back or by doing something similar with alpha blending and GL_ONE, GL_ONE, it requires a readback and software addition on the CPU.
The business of coarse z optimization makes the number you get less meaningful these days. You may want to do this test with depth testing on rather than off, but it still won’t give you a perfect answer because of the approximate nature of coarse z elimination of fragments.
Doesn’t hp_occlusion_query (or something similar) give you the number of pixels drawn?
Charles
Histogramming of written fragments would be very useful for deciding on f-stop/exposure settings. Unfortunately, it’s un-clear how to properly do histogramming of floating-point fragment data in hardware… maybe one sample point per exponent value?
“On any hardware you can count pixels by either incrementing the stencil buffer back or by doing something similar with alpha blending and GL_ONE, GL_ONE, it requires a readback and software addition on the CPU.”
Histogram was looking much faster than that. Too bad it cannot be used 
“The business of coarse z optimization makes the number you get less meaningful these days”
This is true if I want to check out brute force fillrate, but this is not what I want to do. I was thinking in using it to measure the texels drawn. In some way, I could figure out how much texels were discarded by early z thus figurng out how much efficient my front to back rendering is. The advantage of doing this was to have the vertex pipes bottlenecks out of the way.
“Doesn’t hp_occlusion_query (or something similar) give you the number of pixels drawn?”
No, the HP just gives true/false. The NV gives you the number you want… And this is nice. Maybe I can try play a little with it. I totally missed out that.
“Histogramming of written fragments would be very useful for deciding on f-stop/exposure settings. Unfortunately, it’s un-clear how to properly do histogramming of floating-point fragment data in hardware… maybe one sample point per exponent value?”
I simply does not get this. I guess it is related to HDR but I don’t think it’s a great problem… Oh well, I simply don’t know anyway.
Thank you everyone for the useful feedback!