Using two shaders, first one is a solely red + green channels with a feedback loop to calculate the chemicals. Then using the first shader's colors to work out the final colors based on the difference between red and green in the first ones. twitter tutorial
Paint with the mouse. expand
https://keith.superhi.com/ HEIGHT 600
See Gray-Scott Explorer for another implementation.
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Natural pattern simulation using the Gray Scott algorithm with WebGL with a interactive simulation. post