Twice usage of i in nested loop

[fetian-code]

I found in the loop of renderCUDA() in backward.cu, you use i twice in a nested loop. I wonder if it may cause an issue, because it seems the i in the inner loop will change the value of i in outer loop.

[hbb1]

Oh Thank you for pointing out this. This will not cause issue because of the properties of C/CUDA. But definitely, we should replace the second $i$ with something like $j$ for avoiding misinterpretation and potential risks.