   shadows and z-sorting of transparent billboards
  I''m planning un using quads textured with partially-transparent images to represent a lot of the trees and foilage in my current project, but i have some questions about rendening these.Firstly, i suppose you''ll have to draw these after the opaque geometry, and z-sort them before drawing, since they will appear in the z-buffer as if they were opaque, thus preventing things drawn behind them from showing up. Is there a better way to do this? I''m planning on having quite a lot of these billboards in my scenes, and sorting them could be a pain in the ass and a burden on the cpu.Secondly, i''d like to have these things cast shadows in a more-or-less realistic way. It seems the standard shadow casting methods rely on the light-blocking objects to be represented in polygons. I could probably hack up some incorrect-but-not-too-disturbing method of blending a darkened gray version of the textures over the geometry that would receive the shadows (since my project has a fixed camera angle), but if there is a proper way to do this i''d be interested.Marijn 