Yon Uriarte wrote: > Hi, > > On Sun, Dec 14, 2008 at 6:12 PM, Heiko Schulz <aeitsch...@yahoo.de > <mailto:aeitsch...@yahoo.de>> wrote: > > > My last cloudset has fewer but larger sprites. I did this because I > noticed that it saves a lot of fps. On the forum Gijs noticed the > same with my cloudset. > > Mores sprites means more alpha and more textures which is always a > fps-killer. No, the cost of blending is proportional to the area blended on the screen, so a few large sprites vs. many small sprites should cost about the same. It is true that it takes longer to sort a large number of sprites, but I'm not worried about the sorting cost at this point. > I'm pretty sure that there is another solution looking to X-plane > which seems to use the same technic for their clouds. > > > > Fewer bigger sprites with few parts of the sprite with 0 < alpha < 1. > One opaque pre-pass drawing front to back with > alpha culling != 1 and blending off to fill up z-buffer then a second > pass back to front with alpha culling < 1 and blending on. > Second pass gets massively z-culled, saving on rop blending bandwidth. > First pass gets also z-culled by itself. > This is a good idea if, in fact, the cloud sprites are mostly opaque. I think we are doing various tricks where the sprites end up being completely transparent. Also, I don't think that the blending stage is a bottleneck for us at the moment. > It's a tradeoff between cpu and gpu fill and blend rate, whatever is > your bottleneck. > Sadly, that changes between machines, so the opaque pre-pass should be a > configurable. Tim
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