Pope Kim Feb 2, 2010
When batching particles in order to boost the performance, we usually make texture pages, or sprite sheets, (it is a giant texture which contains all textures used for the particles. you can easily use the sub images you want by playing with UV coordiate on vertex data), to minimize the number of draw calls. However, you can go one step further and even batch particles with two different blend modes, alpha and additive blend mode, together and draw'em as one draw call.
That's when pre-multiplied alpha becomes handy. I was planning to write about this, but Shawn Hargreaves already covered this topic a couple of months ago. So here is the link. Enjoy :)