BSP Tree question

[aurora]

Once you've constructed a BSP tree how do you render it?

on this site

ftp://ftp.sgi.com/other/bspfaq/faq/bspfaq.html#9.txt

they show some pseudo code for rendering a bsp tree, and I was wondering if rendering it requires a dot product per polygon? And if that's the case why are they efficient?

Any help would be apprechiated.

[Fool Running]

The way I understand it (not that I'm an expert :roll: ) you just need to check whether the node of the BSP tree lies in the viewing area, not each individual polygon (i.e. the cube that represents the polygons) by going through the tree. It should be very fast to do that. :lol:

[aurora]

Thanks for the reply.

If I the way I'm understanding is correct then it is pretty slow compared to a bounding box method..

The way I see it is that it uses a dot product per node in the tree except the leafs, to check if the camera is in front or behind the nodes..

But if what I'm saying is true it wouldn't explain the popularity of the method, there must be some other trick I'm not seeing here..

It would still be nice to get some more replies if that's possible?

[tomb]

Bsp trees is not a popular method used in rendering any more. That paper you linked to is almost 10 years old. It's outdated. It's excelent when doing software renderers because you can render the polygons perfectly back to front. So you don't need a depth buffer wich can double the fillrate. It is still used for collision detection since raytracing can be speeded up greatly.

[aurora]

Thanks for the reply, I think I understand now.