Hi, I just thought about some techniques to use in my 3d-engine. The first one was to use octrees, because collision-detection would be really easy and clipping away big parts of the world also wouldn''t take too many cycles. So, additionally, I''d use BSP-Trees in each of the octree-nodes and also use portal-rendering. That should normally be relatively fast, shouldn''t it ? For the outdoor-rendering part, someone suggested me R-Trees, could someone explain them to me ? CU Graphix Coding @ Skullpture Entertainment

I would have to say that combining BSPs, octrees and portals would be doing way too much. Using octrees or BSPs inside a portal engine isn''t too bad to implement, and indeed has some benefits. I''m not sure how you''d handle sticking a protal system inside an octree though, or what the benefit would be. Are you having different lists for display and collision?

Hi,
about the portal rendering with Octrees, the portal-rendering would minimize the PVS and using octrees, I could easily clip away the rest of the polygons which are not in the viewing frustum. I''d split the data in each of the cell into an octree, so that I''d have the same number of cells and octrees.

For collision, checking a cube against another one isn''t that hard. If it doesn''t collide with one parent-node, it can''t collide with a child-node, so that would make things really easy. About BSP-Trees in Octrees, you would have all benefits of BSP, but could easily clip away big parts of the world data, and I think this should make things fast.

CU

Graphix Coding @
Skullpture Entertainment

Using a BSP into an octree seems useless to me, because when using a BSP alone, you can also quickly cull large parts of geometry. Portals are very nice for indoor scenes, not outdoor, and a good recursive portal set leaves an almost perfect visible set.

For my new engine I have planned to use octrees as the main culling method since it is fast and works quite well. For determining a PVS within the view frustrum, I planned on using occlusion beams. These two mechanisms should give me a set of polygons that is not too far off of the perfectly visible set and should not cost many CPU cycles to calculate. It is also reasonably suited for outdoor rendering (which portals are not), it is suitable for completely automatic generation of the scene description out of polygon soup (also not possible with portals)and it is usable with dynamic ''actors'' (which BSP''s are not).

DaBit.