[ODE] Terrain: collision test culling

[Hannes Norda]

Hi,

have a look at collide/category bits 
http://www.ode.org/ode-latest-userguide.html#sec_10_5_1

They let you cull collisions early, just before the AABB-test I think.

Also you could try to put all your static geometry in one space and 
dynamic (and static you still wanna check against 'static world') in 
another space.

Now when you check for collisions you just collide the dynamic with the 
static and then the dynamic with itself. Thus not checking for 
collisions between static world at all.

http://www.ode.org/ode-latest-userguide.html#sec_10_5_2

pseudo:
dSpaceCollide2(dynamicspace, staticspace)
dSpaceCollide(dynamicspace)

If you use the second version it is a good idea to still use 
collide/category bits and cull collisions that you don't want, maybe 
between different dynamic objects, like camera vs enemyshots and so on.

I also built my staticspace with subspaces, based on the octree I use 
for rendering.

Hope this helped, sunday morning and no coffee yet.

/Hannes

johnmcTemp at netscape.net wrote:
> Hi. My name is John and this is my first time posting. Ive been using ODE for 
> about 2 weeks. Currently just working on getting better knowledge and 
> testing performance with different terrain sizes to see what I can shoot for on my PC
> as far as a small 3d game.
> 
> I am wondering HOW I call reduce the number of NearCollisionCallback() calls 
> each simulation. Currently, all I am doing is inserting 'chunks' of terrain as trimesh
> geoms into a space. Depending on the space, the number of calls just in these static
> geoms 'colliding' with each other can quite litterly bring my application to a 
> screaching halt (0 to 1 fps).
> 
> So I have some data here, and if possible, would like to see what some of you out
> there that have had experience in terrain chunks, what I may do to improve
> upon my situation. My curiousity is in the number of callbacks every tick. I am really
> not sure why there are so many possible collisions between static geoms, and whether
> there is a simple solution.
> 
> Thanks, and any comments or questions would be great.
> 
> ///////////////////////////////////////////////////////////
> I much cleaner html version can be found here:
> http://home.earthlink.net/~gqjohnm/ODETerrainResults.htm
> 
> ///////////////////////////////////////////////////////////
> Text version in case website is down (excuse the crappy formatting, see html version above):
> 
> [ODE Space Type]          [Num terrain trimesh geoms] [Num NearCollisionCallback() calls] [Num dCollide() collisions]
> Terrain Size = 65x65
> Simple with testing types                           4                                   6                           0
> Simple w/o testing types                            4                                   6                           6
> QuadTree with testing                               4                                   2                           0
> QuadTree w/o testing                                4                                   2                           2
> 
> Terrain Size = 129x129
> Simple with testing types                          16                                  42                           0
> Simple w/o testing types                           16                                  42                          39
> QuadTree with testing                              16                                  12                           0
> QuadTree w/o testing                               16                                  12                          12
> 
> Terrain Size = 256x256
> Simple with testing types                          64                                 207                           0
> Simple w/o testing types                           64                                 207                         186
> QuadTree with testing                              64                                  56                           0
> QuadTree w/o testing                               64                                  56                          56
> 
> Terrain Size = 513x513
> Simple with testing types                         256                                 918                           0
> Simple w/o testing types                          256                                 918                         658
> QuadTree with testing                             256                                 240                           0
> QuadTree w/o testing                              256                                 240                         240
>      
> TERRAIN DETAILS:     
> Terrain is broken up into 33x33 chunks. Each chunk creates an ODE trimesh geom and adds it to the space/world. 
> The reason for the odd numbers is so when terrain is broken into chunks, each will have even numbers, such as 0 to 32, or 32 to 64,.. 
> For quadtree spaces, the center is at 0, with extents being equal to terrain size.    
> The number of levels deep should be such that at all the chunks fit perfectly at the bottom/deepest level. Here are some numbers: 
> Terrain size = 65x65 chunks = 4 total, 2 across Quadtree size = 65x65 Quadtree depth = 2  
> Terrain size = 129x129 chunks = 16 total, 4 across Quadtree size = 129x129 Quadtree depth = 3  
> Terrain size = 257x257 chunks = 64 total, 8 across Quadtree size = 257x257 Quadtree depth = 4  
> Terrain size = 513x513 chunks=256 total, 16 across Quadtree size = 512x512 Quadtree depth = 5  
>      
> NEARCOLLISIONCALLBACK DETAILS ("With/Without Testing"):     
> I use the basic NearCollisionCallback() given in most of the simple examples from ODE.   
> The only difference is that I set classification, in the geom paramater, so I can identify what the geom is, such as a 'terrain chunk'. 
> So, during the NearCollisionCallback(), if neither of the geoms are spaces, then next I test if both are terrain chunks.   
> If so, then early out! I don’t want terrain chunks colliding with each other!!   
> 
> 
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