Here is a little more info: http://software.primefocusworld.com/software/support/krakatoa/main_controls.php#Load_Percentage
It keeps every Nth particle, but it occurs very late in the stack of operations so all particles are still loaded, colored, culled, transformed, KCM’d, etc. The density is multiplied by 1.0/Fraction, so with 10% global load each particle will have 10x the density.
Which parts of Krakatoa are the slowest for you? Are you familiar with the profiling results shown in the Krakatoa Log Window during a render?
As it turns out, the density compensation isn’t documented AND isn’t consistent with the PRT Loaders which don’t change the density when loading. I personally think that if you want less dense particles its pretty easy to set the density appropriately with the myriad of other options for tweaking density.
The >Iterative mode button has some options for lowering the render resolution and trying to compensate the density accordingly. http://software.primefocusworld.com/software/support/krakatoa/iterative_mode_scale_output.php
EDIT: Bobo says this feature probably doesn’t do anything to the density in most situations. Apparently it was only for tweaking the density of additive renders.
Can you elaborate on this? The PRT Loader is effectively a diskcache, isn’t it? A PRT Volume cache can be created by saving the particles to disk. Granted its difficult to set up a scene, THEN save the particles from a single object to disk, but we are working on making that easier.
You should be able to mess around with the resolution of the PRT Volume to improve speed and can compensate density accordingly.
For example, if you double the ‘Spacing’ value in the PRT Volume you can increase the density by 8 times (A 1x1x1 cube became an 2x2x2 cube) and expect a similar image when viewed from a sufficient distance.
If your geometry is complicated I imagine that the majority of the time is spent pre-processing the geometry, and that is heavily related to the ‘Spacing’ value in the PRT Volume. That’s unfortunate too since that part is the least responsive once it has started.