Hi All.
I've added this to the Ashunder collection as well but I thought I'd post a copy here as well.
After messing around with complex leaf surfaces for trees (which are working nicely) I aplied the same surfaces to leaves. It looked good as well, but the render times were ridiculous (10-15 minutes per clump) so I went back to my basic grass surface.
What I've added this time is a duplicate surface with a different colour, comined with a mixer. This allows for blending colours via a mask at a leaf level rather than just changing the colour for the entire population. Thus with one population (for example) you could have the proportion of dead grass blades in each object increase towards the edge of a flow map... or animating a transition of colour by changing individual leaves in conjunction with the overall colour of the object.
I made a basic 10 frame animation to demonstrate this (2 fps)
http://www.path.unimelb.edu.au/~bernardk/tgdemo/mix_grass.avi (102kb)
<edit> redone with 3ivx codec. Here's a collage of the frames for anyone else with codec issues
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The mixer function was a white surface layer with a fractal breakup.
First frame: Coverage = 0, fractal breakup = 2
Last frame: Coverage = 1, fractal breakup = 0
This approach should also be useful for my tree leaf surfaces, and provides a simpler means of mixing the colours with the flexibility of whatever masks you use.
Once again.... please send me any improvements if you make any.
Enjoy