Depth buffers only work well for opaque objects, which cover each other completely. With partial coverage or blending, multiple objects could end up contributi

Depth buffers only work well for opaque objects, which cover each other completely. With partial coverage or blending, multiple objects could end up contributing to a pixel in an order-dependent way (e.g., if you're viewing an anti-aliased leaf edge under the surface of water through a window). The depth buffer, which only stores a single depth, doesn't solve this problem directly -- you can use it to render each transparent layer one-by-one ("depth peeling"), but this can be slow.