IME, crackle will produce a passable stained glass-ish effect and MIGHT 
be good for scenes where you're not looking right at the window, but the 
only way to get a really authentic-looking stained glass window is to 
use a photo as an image map, or make your own in an image editor or 
something similar.

The reason is that most stained glass windows aren't truly broken up 
into random cells; instead, they use thick leading to create heavy 
outlines, like a picture in a coloring book, and then fills in those 
outlines with colored glass in a way that may OR MAY NOT be random. 
There's no simple way to do this algorithmically, and in order to even 
try, you would need to create a texture with some kind of edge-finding 
ability, to create the heavy outlines.

(If you wanted to cheat halfway, I suppose you could create an image map 
with just the outlines, and then use a crackle or turbulated cells 
pattern to fill in the colored areas.)

As long as I'm on this subject, I should point out that a lot of stained 
glass isn't crystal clear or consistently colored. A good deal of 
stained glass is milky-looking, or has milky-looking swirls in it; some 
is clear but too dark to really see anything through, and small 
variations in color, color intensity, and transparency/milkiness are 
common. If you don't already have a pretty good idea of what stained 
glass is really like, it would be wise to hunt down some photos to study.

-Xplo

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