Eigen2 Debug mode

Eigen's main page claims "Disabling asserts, by defining -DNDEBUG or -DEIGEN_NO_DEBUG, improves performance in some cases."
What they mean is that we need to call g++ with the -DEIGEN_NO_DEBUG option.

In this post, we test the effect of disabling asserts on a few test scenes. The first scene is a 512x512 render of a refractive sphere with reflective cornell room walls. The second scene is the same room, but 9 refractive spheres. The third scene is obtained by rendering the second scene at 1024x1024 with shadow rays. All scenes have 2 light sources.

Average running times with default settings (eigen in debug mode), were 3.6 seconds for the first scene, 4.3 seconds for the 2nd scene and 47 seconds for the third scene.



This reduces code run times pretty drastically (2.4, 2.8 and 33 seconds approximately for the three scenes described above). There is a clear 30% and above performance improvement when debug mode is disabled. Anyway, debugging with eigen is a nightmare (way too much boilerplate to sift through), and I use my own Vector library while doing serious debugging.