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Archive Notice: This thread is old and no longer active. It is here for reference purposes. This thread was created on an older version of the flipcode forums, before the site closed in 2005. Please keep that in mind as you view this thread, as many of the topics and opinions may be outdated.

July 10, 1999, 03:15 PM

I am confused on how new gaming engines use BSP trees to elliminate overdraw. The point of the BSP is to get perfect depth sorting I thought. I read quake engine games then use a span buffer to keep track of the polygons that are drawn, in a front to back order. However hardware engines will run slow with this method due to state changes involved when rendering front to back with all the texture switches. Do they just use a delayed rendering where the faces are calculated front to back, but not drawn then - but ordered by texture type and drawn later? Does the BSP help out that much, or could standard depth sorting w/face splitting be nearly as fast if using a span buffer in this approach?

Gilles Berguet

July 11, 1999, 12:37 PM

In Quake engines, the BSP is used for its space division capabilities.
For each leaf of the bsp (polyhedre) a PVS is precomputed (PVS = Potentially Visible Set = Polygons which can be view when the camera is in this area, watching in every direction).
PVS calculation is quite slow and complex too program anyway.


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