a rendered version of the rain test with wetmaps.
the wetmap is created as described in this tutorial: vimeo.com/5801619
ive tried to add some waves to the wet are.
It's done with another particle system that holds the position where the rain drops collide with the ground with a low life expectancy that is written to a pointcloud file and read by the shader. the shader uses the life attribute of the particles to drive the phase of a sine wave centered at the particles position.