* The termination probability of paths can be determined based on the [overall throughput](http://15462.courses.cs.cmu.edu/fall2015/lecture/globalillum/slide_044) of the path (you'll likely need to add a field to the Ray structure to implement this) or based on the value of the BSDF given wo and wi in the current step. Keep in mind that delta function BSDFs can take on values greater than one, so clamping termination probabilities derived from BSDF values to 1 is wise.
* To convert a Spectrum to a termination probability, we recommend you use the luminance (overall brightness) of the Spectrum, which is available via Spectrum::illum()
* To convert a Spectrum to a termination probability, we recommend you use the luminance (overall brightness) of the Spectrum, which is available via `Spectrum::luma`
* We've given you some [pretty good notes](http://15462.courses.cs.cmu.edu/fall2015/lecture/globalillum/slide_047) on how to do this part of the assignment, but it can still be tricky to get correct.
