# Assignment 4 Discussion

Don't hesitate to ask questions.

Q1: The first question says "L(phi, theta) = cos(theta) when theta > PI/2 and L(phi, theta) = 0 otherwise." Shouldn't this be for theta < PI/2, so that it's cosine-weighted hemisphere sampling, which is more appropriate here? If theta > PI / 2, the arrangement doesn't make much sense - the luminance would be negative! And Shouldn't we also be weighting by the cos(theta) term in the radiance function (or is this already implied)?

I agree (PaulTarjan)

### A1:

It should be `theta < PI/2`. It was a mistake in the assignment and has now been fixed. The intent of the question was for you to sample with respect to `L = cos(theta)`, which is exactly what `infinitesample.cpp` does. However, it is true that the integral you are estimating does contain an additional term `cos(theta)`. In this case, it is possible to analytically sample with respect to more than just the value of `L`. If you choose to do this, please state so explicitly.

Q2: I've extracted the "string sample" parameter from the paramter set in directlighting.cpp, but how do I access this data when I'm doing the re-weighting in transport.cpp? Can I just cast around the Light * object? (BillDwyer)