One way collision meshes?

[GameQ]

Is it possible to have one way collisions? I thinking of a a typical platform game where the characters can pass through a platform while going up, but land on top of it going down.

If it isn't supported directly by bullet, then does anyone have a good efficient solution. My first guess is to set the characters collision filter mask based on the current Y velocity.

Thanks,
~GameQ

[scottw]

The filter mask is a good idea if the object you are moving is dynamic. Have you implemented it that way, or found a better solution?

I am currently trying to do this with a kinematic object. I am using sweep checks and ignoring certain types of collision based on my object's y-velocity.

Does anybody know of any other way of setting up a one-way collison other than dyamic/mask or kinematic/manual sweep-checks?

-scott

[sparkprime]

Here's some code i use to do this for gimpact meshes. It hasn't killed anyone yet.

Code: Select all

 121 void process_contact (btManifoldPoint& cp,
  122                       const btCollisionObject* colObj,
  123                       int partId, int index, bool gimpact)
  124 {
  125         (void) partId;
  126         (void) index;
  127         const btCollisionShape *shape = colObj->getCollisionShape();
  128 
  129         if (shape->getShapeType() != TRIANGLE_SHAPE_PROXYTYPE) return;
  130         const btTriangleShape *tshape =
  131                static_cast<const btTriangleShape*>(colObj->getCollisionShape());
  132 
  133 
  134         const btCollisionShape *parent = colObj->getRootCollisionShape();
  135         if (parent == NULL) return;
  136 
  137 
  138         btVector3 normal;
  139         tshape->calcNormal(normal);
  140 
  141         const btMatrix3x3 &orient =
  142                 colObj->getWorldTransform().getBasis();
  143 
  144         normal = orient * normal;
  145 
  146         btScalar dot = normal.dot(cp.m_normalWorldOnB);
  147 
  148 
  149         if (gimpact) {
  150                 if (parent->getShapeType()==GIMPACT_SHAPE_PROXYTYPE) {
  151                         if (dot > 0) {
  152                                 cp.m_normalWorldOnB -= 2 * dot * normal;
  153                         }
  154                 }
  155         } else {
  156                 if (parent->getShapeType()==TRIANGLE_MESH_SHAPE_PROXYTYPE) {
  157 
  158                         btScalar magnitude = cp.m_normalWorldOnB.length();
  159                         normal *= dot > 0 ? magnitude : -magnitude;
  160 
  161                         cp.m_normalWorldOnB = normal;
  162 
  163                 }
  164         }
  165 
  166 }
  167 
  168 bool contact_added_callback (btManifoldPoint& cp,
  169                              const btCollisionObject* colObj0,
  170                              int partId0, int index0,
  171                              const btCollisionObject* colObj1,
  172                              int partId1, int index1)
  173 {
  174         (void) colObj1;
  175         (void) partId1;
  176         (void) index1;
  177         // 0 is always the gimpact?
  178         // 1 is always the scenery?
  179         process_contact(cp, colObj0, partId0, index0, true);
  180         process_contact(cp, colObj1, partId1, index1, false);
  181         //std::cout << to_ogre(cp.m_normalWorldOnB) << std::endl;
  182         return true;
  183 }

The idea is that the triangles are one-way, so that you don't get objects rattling around inside your vehicle body.

[sparkprime]

Note, this also contains the 'bumpy triangle mesh' fix, search forums for more info