Any pointers on how to get this to simulate rays of sunshine through an semi-opaque surface with holes(sheet of paper,water,wood,fence,stone etc)

I want to be simulate sun rays penetrating a material which has holes in it.

Here is the sketch
http://openprocessing.org/visuals/?visualID=23478

Here is the code in one compact link
http://emoc.org/opcode/23478code

Any one that needs the code pasted here can indicate such.

Thanks.