QuadTree Object Occlusion

How expensive is it to use 4 planes to define the left,right, top, and bottom viewing volume to determine whether something is in or out of the volume? The idea is to use the x,y,z location a normal vector for the plane, then just check to see if the normal points outside the box, or inside the box. A normal of length zero would mean that the object should be drawn as it is on the line.

Look at the portal example for finding if a quad is visible.
You could also do it by transforming the points yourself, as in example 17. Check the flags of the vdata structure. If flags are 0, the vertex wasn''t clipped and is visible.

I really don''t want to use a static quadtree structure for the objects. I want everything to move around and possibly be destroyed.

For example if a regular grid was used, an object that moves would quickly be able to figure out what square it was in.
Big objects that cross many squares could have a flag and just use the regular bounding box check.

Chris

Hi,
The way it works at the moment, works nicely for static objects. I think I can write it so that it accounts for moving objects, if I predefine the minimum Quad Node size as 1 grid, and store the Nodes neghbours within the node.
I was more writing it to cope with large numbers of trees, rocks etc, that won''t move, and if they are destroyed, remain in the same position.




FYI Chris, the sim I am currently working on has destroyable objects, works like this.

Create pro original object, blah.PRO.
Create Polytope object, blah.HIT.
Create Explosion animation for object, blah.EXP. (Quite good, can use dynamics within 3DStudio to get some nice object exploding anim)

Then within the sim, I can change the Object pointer from the .PRO to the .EXP when the object is destroyed, and play the animation of the EXP until the last frame.

I also made allowances for sub objects, ie a boat, where the hull is the main object, and there are 3 different areas on deck that you can destroy, which are linked to the hull.

May post some shots if anyone is interested.
Cheers
Darrin

Actually the more I think about the regular grid method, the more I am starting to like it.
Will look at going down this path. (Can also use a modified form of the Quad Algo to determine visible grids, which should improve culling speeds.)

Cheers
Darrin

in the present LS do tiles which are not seen also rendered? i.e terrain parts which are in the viewing distance but are not seen due to obstuctions (like undulations) also transformed and rendered.

Yes

It would be good if they were not ..maybe in PR4

Sorry the engine doesn''t work that way. Each section of the quadtree has a bounding box that is tested against the viewport for visibility. There is no easy way to check if part of the landscape is behind a hill, especially with deformable terrain.

With hardware T&L there is no problem with how much terrain is drawn. The slow parts right now are the hundreds of trees and other objects that I want to draw. I just added LOD switching which helps a bit, however I think I need to add in triangle stripping to get the speed I want.

This may be a little off beat, but has anyone looked at using ROAM not for the terrain but for objects like buildings?