Is it possible, that two or more fragments (perhaps from different primitives) with the SAME xy target (screen) coordinates are ever being executed concurrently by multiple GPU threads?
It sounds weird, let me rephrase it just to be sure
Say I submit 2 triangles that will project to the very same target xy pixels (they might or might not have different z (depth)).
1. For each of the 6 vertices a vertex shader will be invoked and all these 6 vertex shaders run at once (there's plenty of groups and units on the GPU, right?)
2. There is no geometry shader (irrelevant). Both triangles will project to the same pixels of the target. Rasteriser rasterises and pixel shaders get invoked...
3. Is there a possibility that two pixel shaders (one for a fragment on triangle 0 and one for another fragment on triangle 1), which want to shade (and possibly write or scatter) at the very same target (screen) location, get executed really concurrently (obviously on different thread groups)???
I suppose yes. I am obviously looking for the worst-case scenario. Am I right? Early-Z, presence of discards and explicit depth-writes and similar peculiarities probably have a say in this.
Next question would be (DX11/GL4) if it is necessary to have ANY output target bound to the output merger, or is it enough to bind 0 RTVs and 1 UAV (OMSetRenderTargetsAndUnorderedAccessViews()). I'm not talking compute shaders.
