Are there tricks for getting proper sort ordering on particle systems?

Question

If you have a bunch of particles to render, using different shaders and/or render states, that have some level of transparency, the naive solution of sorting all particles by depth can be extremely inefficient since it is likely to turn a few large batch draw calls into a multitude of smaller batch calls which have expensive render state switches between those draw calls.

I know of a few ways to help fake things such as sorting particle batches by their emitter location, or using something like additive blending, which gives the same result regardless of draw order.

I also know there are some techniques out there to attempt order independent transparency, often being an approximation, requiring a (sometimes unbounded) amount of memory, or some combination thereof.

Does anyone know any pragmatic solutions (fast/low extra memory requirements/absolute correctness not required) for dealing with this situation?

Answer 1

First option should be to make all particles able to go through the same pipeline. Perhaps with an uber shader. That way you can batch them all.

Positive ieee floating point numbers can be sorted like unsigned integer. And there are O(n) algorithms to sort those for example radix sort.

Answer 2

Sort the particles by Z each rendering cycle using an algorithm such as bubble sort which is good when element changes position in small steps. If the perspective does not change much the errors would be few enough over time to be unnoticable. The technique is easy to configure between quality and performance dependning on the target platform by adjusting how much sorting is performed each cycle.