What about this ?
10.5.1. Category and Collide Bitfields
Each geom has a ``category'' and ``collide'' bitfield that can be used to assist the space algorithms in determining which geoms should interact and which should not. Use of this feature is optional - by default geoms are considered to be capable of colliding with any other geom.
Each bit position in the bitfield represents a different category of object. The actual meaning of these categories (if any) is user defined. The category bitfield indicates which categories a geom is a member of. The collide bitfield indicates which categories the geom will collide with during collision detection.
A pair of geoms will be considered by dSpaceCollide and dSpaceCollide2 for passing to the callback only if one of them has a collide bit set that corresponds to a category bit in the other. The exact test is as follows:
// test if geom o1 and geom o2 can collide
cat1 = dGeomGetCategoryBits (o1);
cat2 = dGeomGetCategoryBits (o2);
col1 = dGeomGetCollideBits (o1);
col2 = dGeomGetCollideBits (o2);
if ((cat1 & col2) || (cat2 & col1)) {
// call the callback with o1 and o2
}
else {
// do nothing, o1 and o2 do not collide
}
Note that only dSpaceCollide and dSpaceCollide2 use these bitfields, they are ignored by dCollide.
Typically a geom will belong only to a single category, so only one bit will be set in the category bitfield. The bitfields are guaranteed to be at least 32 bits wide, so the user is able to specify an arbitrary pattern of interactions for up to 32 objects. If there are more than 32 objects then some of them will obviously have to have the same category.
Sometimes the category field will contain multiple bits set, e.g. if the geom is a space them you may want to set the category to the union of all the geom categories that are contained.
10.5.1. Category and Collide Bitfields
Each geom has a ``category'' and ``collide'' bitfield that can be used to assist the space algorithms in determining which geoms should interact and which should not. Use of this feature is optional - by default geoms are considered to be capable of colliding with any other geom.
Each bit position in the bitfield represents a different category of object. The actual meaning of these categories (if any) is user defined. The category bitfield indicates which categories a geom is a member of. The collide bitfield indicates which categories the geom will collide with during collision detection.
A pair of geoms will be considered by dSpaceCollide and dSpaceCollide2 for passing to the callback only if one of them has a collide bit set that corresponds to a category bit in the other. The exact test is as follows:
// test if geom o1 and geom o2 can collide
cat1 = dGeomGetCategoryBits (o1);
cat2 = dGeomGetCategoryBits (o2);
col1 = dGeomGetCollideBits (o1);
col2 = dGeomGetCollideBits (o2);
if ((cat1 & col2) || (cat2 & col1)) {
// call the callback with o1 and o2
}
else {
// do nothing, o1 and o2 do not collide
}
Note that only dSpaceCollide and dSpaceCollide2 use these bitfields, they are ignored by dCollide.
Typically a geom will belong only to a single category, so only one bit will be set in the category bitfield. The bitfields are guaranteed to be at least 32 bits wide, so the user is able to specify an arbitrary pattern of interactions for up to 32 objects. If there are more than 32 objects then some of them will obviously have to have the same category.
Sometimes the category field will contain multiple bits set, e.g. if the geom is a space them you may want to set the category to the union of all the geom categories that are contained.