I was looking at supreme commander, and how they have rage circles that are painted on the terrain for each unit, and I was curious on how they did that ?

I am thinking they might be using a textured quad with a circle shape in the alpha buffer, and then stretch that to what they need, and use a shader to get it the color they want but, that would produce jaggies if the texture was too low of a res.

Doing the "normal" way of using a vertex array seems to be way too slow, since they would have to factor in the terrain height.

Are they doing something special here ?
Here is a pic:

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