I found the incorrect calculation of the indirect lamp emission, which causes white pixels in a rendered image
Testing the patch with the scene shared by pafurijaz user here:
I hope I have applied the patch correctly, otherwise my apologies if it was not so.
Blender whitout the patch:
There are less fireflies, but something in lighting has also changed. See especially the windows.
Just in case, here the image with blender unpatched, but Clamp indirect=8
The change seems strange to me. For the rays which are not marked to be skipped from MIS (PATH_RAY_MIS_SKIP) you are kind of accommodating for ls.pdf twice (due to the power heuristic above). For the rays which are marked to be skipped from MIS you're accommodating for ls.pdf.
Not sure how this is supposed to work.
It may be that there is something to be fixed or improved here. The first thing I would suggest to investigate would be rendering the two MIS components separately, by replacing power_heuristic() by 0 or 1, that might reveal something. On the other hand it might just be a case where both MIS components are noisy.
thank you for comments.
I still think the L value from direct_emissive_eval function is too big for adding to emission value and has to be smaller value.
In the scene Vray_vs_Cycles_vs_Maxwell.blend are two types of white pixels (the first from direct lamp and second from indirect lamp). I tested it on all frames of scene 01_04_B from Agent327 and I think it worked. The white pixels had >>100 value for each channel of RGB.
I will continue to investigate in this area.