I have implemented something, which should hopefully (after testing and bugfixing) be able to reproduce the behavior of both systems. Now it's time to test.
Is there any simple way to test the whole volume on the projected light?
I mean, ordinary testing against floor only shows light behavior on one planar section, and I'd like to see many sections at once. I know that this is exactly what "volumetric light" should achieve, but maybe there is some stupid way, like putting many small objects, or several transparent planes, or maybe grids...