I've been trying to understand this so that I can optimize models with transparent portions as best as possible and I'm having a hard time finding info.
Where exactly is the drain from overdraw issues? The name "overdraw" would seem to imply that the more transparent space that is rendered on screen, the worse it is, if that is the case does it help to add geometry to reduce the amount of transparent space on screen? Also is it ONLY the amount of transparent space that gets rendered on screen? Does the issue affect the entire material, or just the portions of the material that are transparent in the alpha mask?
Help illustrate the point:
(Sorry for busting out the good old transparent magenta)
A) where we're reducing geometry as much as possible, but it results in more transparent space being rendered
We've doubled the geometry count to make the shape fit the model better, reducing the transparent space being rendered
C) Exact same size as B, but it is completely transparent space unlike B which has an opaque portion of the material in it.
1) Between A and B which is the more ideal solution? More geometry for a better shape? The main question I'm trying to answer is, is the amount of transparent space on screen important to overdraw, and is adding more geometry to match the shape a worthwhile effort? I'm not looking for a hard rules to follow, I'm just trying to understand where the performance problem is.
2) Are B and C equivalent performance wise? Or does the fact that there is an opaque area of the texture make B more attractive? The question I'm mainly getting at here is whether or not the entire material becomes a drain on performance, or if JUST the transparent area is? Meaning would it be better for example if you were making a tree, to seperate the trunk texture (which is probably 100% opaque) from the canopy leaf textures, or does it make no difference and you can include them all in the same material?
I apologize if this is confusing, I had a hard time trying to think of the right way to ask this question.