Seeing as we wanted rain i thought it would be good to check around for tutorials or the like, and voila there was plenty of information on how to create the effect. I chose to go with an alpha plane solution, mainly because it’s the easiest way to implement it in addition to being far less of a performance hog.
The effect was very simple to achvie.
1.) Black and white picture of rain, also use the nvidia photoshop plugin to create a normal map from it as it will be used later on
2.) FBX file with a simple plane that can be imported to UDK
3.) Some work in the material edtior
Basically what happens is that the texture sample (the texture we created) is tiled a different number of times across the U/V axis and then panned down to create the moving effect. The example projects in UDK has a more advanced version of this material that looks roughly the same but has a much larger node network.
The material in itself is translucent and two sided with no lighting.
It’s not perfect and still needs more work to make it look better, using more then one texture for example and fading the edges better. But for now this will do more then well.