Why is depth test not done on geometry before rasterization?

by Colin   Last Updated January 12, 2018 17:13 PM - source

It seems the only time depth is used to discard data is during rasterization, i.e. at the fragment level.

In the geometry stage, I've only see culling and clipping of vertices. Is it not possible to determine whether if a triangle is behind another triangle using just vertex data (depth?) and discard if so? Wouldn't this save all the work later in scan conversion?

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