Visualize ray tracing


I want to visualize ray paths in Blender in a similar way to what this ray tracing web application achieves:

In a blender conference talk, Paul Melis showed a solution to this (which is exactly what I need):
But I can’t find any available script or add-on that actually achieves this result.

Does anyone know how I can visualize ray tracing in blender?

You cannot access to that information from addons or scripts… you need to hook a watch code inside the render routines, and recompile Blender (which was what Paul Melis did). Just remeber that the amount of rays being throwned by Cycles is enormous!

how would one hook a watch code to the render routines? I too am trying to make a visualization like what Zazizizou was asking for

what is this web app btw?

I believe this is it