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Excluding certain models from ray casting


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#1 Medo3337   Members   -  Reputation: 665

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Posted 25 November 2012 - 05:43 PM

I need to exclude certain models/meshes from ray casting, this might include bounding box, glasses, certain models, etc...

Any sample code for ray casting with exclude list?

I'm using Bullet ray casting.

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#2 Bacterius   Crossbones+   -  Reputation: 8694

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Posted 25 November 2012 - 06:08 PM

Not sure you can exclude glass from ray casting, it doesn't just let light through, it refracts it. This is negligible if you are looking at an ordinary window model, but if you consider large blocks of glass (or even water) it's probably necessary to trace the ray through multiple bounces, otherwise you'd end up being able to see an enemy which cannot see you (which is impossible).

The slowsort algorithm is a perfect illustration of the multiply and surrender paradigm, which is perhaps the single most important paradigm in the development of reluctant algorithms. The basic multiply and surrender strategy consists in replacing the problem at hand by two or more subproblems, each slightly simpler than the original, and continue multiplying subproblems and subsubproblems recursively in this fashion as long as possible. At some point the subproblems will all become so simple that their solution can no longer be postponed, and we will have to surrender. Experience shows that, in most cases, by the time this point is reached the total work will be substantially higher than what could have been wasted by a more direct approach.

 

- Pessimal Algorithms and Simplexity Analysis


#3 Medo3337   Members   -  Reputation: 665

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Posted 26 November 2012 - 12:30 AM

@Bacterius: I would appreciate if you could point me to sample source code for excluding certain models, I have been trying to use raycasting "All Hit" callback and go through the hits from 0 to the number of hits but it's not working as expected.

#4 Steve_Segreto   Crossbones+   -  Reputation: 1519

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Posted 26 November 2012 - 01:33 AM

Sigh ... this is a repost from a previous response about Pathfinding in Bullet.

Pretty much you can just use dynamicWorld->RayTest() for ray to world testing. Here's an example of how to do that and also setup some collision filters (like how to dynamically select one single object to ignore (collision filter) while ray testing against everything else).
typedef struct _COLLISION_DATA
{
    class CCollideeInstance    *m_pCollideeInstance;
    class CCharacterController *m_pDynamicObj;
    class btCollisionObject    *m_pRigidBody;
} COLLISION_DATA;
#define GET_GHOST(x) (btGhostObject *)(((COLLISION_DATA *)x->getUserPointer())->m_pRigidBody)
class GhostPairCallback : public btOverlappingPairCallback
{
public:
GhostPairCallback()
{
}
virtual ~GhostPairCallback()
{
}
virtual btBroadphasePair* addOverlappingPair(btBroadphaseProxy* proxy0,btBroadphaseProxy* proxy1)
{
  btCollisionObject* colObj0 = (btCollisionObject*) proxy0->m_clientObject;
  btCollisionObject* colObj1 = (btCollisionObject*) proxy1->m_clientObject;
  btGhostObject* ghost0 =   btGhostObject::upcast(colObj0);
  btGhostObject* ghost1 =   btGhostObject::upcast(colObj1);
  if (ghost0 && ghost0 != GET_GHOST(colObj1))
	    {
   ghost0->addOverlappingObjectInternal(proxy1, proxy0);
	    }
  if (ghost1 && ghost1 != GET_GHOST(colObj0))
   ghost1->addOverlappingObjectInternal(proxy0, proxy1);
  return 0;
}
virtual void* removeOverlappingPair(btBroadphaseProxy* proxy0,btBroadphaseProxy* proxy1,btDispatcher* dispatcher)
{
  btCollisionObject* colObj0 = (btCollisionObject*) proxy0->m_clientObject;
  btCollisionObject* colObj1 = (btCollisionObject*) proxy1->m_clientObject;
  btGhostObject* ghost0 =   btGhostObject::upcast(colObj0);
  btGhostObject* ghost1 =   btGhostObject::upcast(colObj1);
  if (ghost0 && ghost0 != GET_GHOST(colObj1))
   ghost0->removeOverlappingObjectInternal(proxy1,dispatcher,proxy0);
  if (ghost1 && ghost1 != GET_GHOST(colObj0))
   ghost1->removeOverlappingObjectInternal(proxy0,dispatcher,proxy1);
  return 0;
}
virtual void removeOverlappingPairsContainingProxy(btBroadphaseProxy* proxy0,btDispatcher* dispatcher)
{
  btAssert(0);
  //need to keep track of all ghost objects and call them here
  //m_hashPairCache->removeOverlappingPairsContainingProxy(proxy0,dispatcher);
}
};
struct ActorFilterCallback : public btOverlapFilterCallback
{
// return true when pairs need collision
virtual bool needBroadphaseCollision(btBroadphaseProxy* proxy0,btBroadphaseProxy* proxy1) const
{
  bool collides = (proxy0->m_collisionFilterGroup & proxy1->m_collisionFilterMask) != 0;
  collides = collides && (proxy1->m_collisionFilterGroup & proxy0->m_collisionFilterMask);
  //add some additional logic here that modifies 'collides'
  btCollisionObject* colObj0 = (btCollisionObject*) proxy0->m_clientObject;
  btCollisionObject* colObj1 = (btCollisionObject*) proxy1->m_clientObject;
	    if (GET_GHOST(colObj0) == colObj1)
	    {
		    return false;
	    }
	    if (GET_GHOST(colObj1) == colObj0)
	    {
		    return false;
	    }
	    return collides;
}
};
void ActorNearCallback(btBroadphasePair& collisionPair, btCollisionDispatcher& dispatcher, const btDispatcherInfo& dispatchInfo)
{
    // Do your collision logic here
    // Only dispatch the Bullet collision information if you want the physics to continue
btCollisionObject* colObj0 = (btCollisionObject*) collisionPair.m_pProxy0->m_clientObject;
btCollisionObject* colObj1 = (btCollisionObject*) collisionPair.m_pProxy1->m_clientObject;
    if (GET_GHOST(colObj0) == colObj1)
    {
	    return;
    }
    if (GET_GHOST(colObj1) == colObj0)
    {
	    return;
    }
    dispatcher.defaultNearCallback(collisionPair, dispatcher, dispatchInfo);
}
D3DXVECTOR3 CPhysicsEngine::CastRayToWorld(
										   const D3DXVECTOR3	 &rayOrigin,
										   const D3DXVECTOR3	 &rayDir,
										   CCollidee		    **hitObj,
										   CCollideeInstance    **hitInstance,
										   CCharacterController **hitDynamicObj,
										   bool				   skipDynamicObjects,
										   bool				   skipBackfaces,
										   CCharacterController  *pSkipObj,
										   D3DXPLANE			 *pHitPlane
										   )
{
    btVector3 rayFromW, rayToW, newRay;
    short oldGroup1;
    short oldGroup2;
    if (pSkipObj &&
	    pSkipObj->getGhostObject() &&
	    pSkipObj->m_sphereCollider &&
	    pSkipObj->getGhostObject()->getBroadphaseHandle()
	    )
    {
	    oldGroup1 = pSkipObj->getGhostObject()->getBroadphaseHandle()->m_collisionFilterGroup;
	    oldGroup2 = pSkipObj->m_sphereCollider->getBroadphaseHandle()->m_collisionFilterGroup;
	    pSkipObj->getGhostObject()->getBroadphaseHandle()->m_collisionFilterGroup = 0x00;
	    pSkipObj->m_sphereCollider->getBroadphaseHandle()->m_collisionFilterGroup = 0x00;
    }
    rayFromW = btVector3( rayOrigin.x, rayOrigin.y, rayOrigin.z );
    rayToW = btVector3( rayDir.x, rayDir.y, rayDir.z );
    btCollisionWorld::ClosestRayResultCallback cb(rayFromW, rayToW);
    if (skipBackfaces)
    {
	    cb.m_flags = 1 << 0;
    }
    *hitObj	    = NULL;
    *hitDynamicObj = NULL;
    newRay		 = rayToW;
    m_dynamicsWorld->rayTest( rayFromW, rayToW, cb );
    if (cb.hasHit ())
    {
	    btCollisionObject *pObj = cb.m_collisionObject;
	    if (pObj)
	    {
		    COLLISION_DATA *pCD;
		    pCD = (COLLISION_DATA *)pObj->getUserPointer();
		    if (pCD && pCD->m_pCollideeInstance)
		    {
			    CCollideeInstance *pInstance = pCD->m_pCollideeInstance;
			    if (pInstance)
			    {
				    newRay = cb.m_hitPointWorld;
				    if (pHitPlane)
				    {
					    D3DXPlaneFromPointNormal( pHitPlane,
						    &D3DXVECTOR3( newRay.getX(), newRay.getY(), newRay.getZ() ),
						    &D3DXVECTOR3( cb.m_hitNormalWorld.getX(), cb.m_hitNormalWorld.getY(), cb.m_hitNormalWorld.getZ() ) );
				    }
				    *hitObj = pInstance->m_pCollidee;
				    if (hitInstance)
				    {
					    *hitInstance = pInstance;
				    }
			    }
		    }
		    //
		    // If we still haven't matched, it's likely we hit a ghost
		    // object.
		    //
		    if (*hitObj == NULL)
		    {
			    if (pCD && pCD->m_pDynamicObj)
			    {
				    if (!skipDynamicObjects)
				    {
					    newRay	 = cb.m_hitPointWorld;
					    if (pHitPlane)
					    {
						    D3DXPlaneFromPointNormal( pHitPlane,
							    &D3DXVECTOR3( newRay.getX(), newRay.getY(), newRay.getZ() ),
							    &D3DXVECTOR3( cb.m_hitNormalWorld.getX(), cb.m_hitNormalWorld.getY(), cb.m_hitNormalWorld.getZ() ) );
					    }
				    }
				    *hitObj	    = NULL;
				    if (hitInstance)
				    {
					    *hitInstance   = NULL;
				    }
				    *hitDynamicObj = pCD->m_pDynamicObj;
			    }
	 }
}
if (pSkipObj &&
		    pSkipObj->getGhostObject() &&
		    pSkipObj->m_sphereCollider &&
		    pSkipObj->getGhostObject()->getBroadphaseHandle()
		    )
{
		    pSkipObj->getGhostObject()->getBroadphaseHandle()->m_collisionFilterGroup = oldGroup1;
		    pSkipObj->m_sphereCollider->getBroadphaseHandle()->m_collisionFilterGroup = oldGroup2;
}
return D3DXVECTOR3( newRay.getX(), newRay.getY(), newRay.getZ() );
}
void Example()
{
    m_defaultContactProcessingThreshold = BT_LARGE_FLOAT;
    m_collisionConfiguration = new btDefaultCollisionConfiguration();
    m_dispatcher = new btCollisionDispatcher(m_collisionConfiguration);
    m_overlappingPairCache = new btDbvtBroadphase();
 
    m_ghostPairCallback = new GhostPairCallback();
    m_overlappingPairCache->getOverlappingPairCache()->setInternalGhostPairCallback(m_ghostPairCallback);
    m_constraintSolver = new btSequentialImpulseConstraintSolver();
    m_dynamicsWorld = new btDiscreteDynamicsWorld( m_dispatcher,
												   m_overlappingPairCache,
												   m_constraintSolver,
												   m_collisionConfiguration
												 );
    m_filterCallback = new ActorFilterCallback();
    m_dynamicsWorld->getPairCache()->setOverlapFilterCallback(m_filterCallback);
    m_dispatcher->setNearCallback(ActorNearCallback);
}


#5 Medo3337   Members   -  Reputation: 665

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Posted 26 November 2012 - 02:43 AM

Hi Steve,

The other question about Pathfinding was completely different (I was trying to implement Pathfinding which has nothing to do with using raycasting while excluding certain models (like they don't exist).

I believe that the above code is not exactly what I'm looking for, here is the prototype of the method that I'm looking for:

void Raycast(btVector3 rayOrigin, btVector3 rayDir, vector<DWORD> excludeModelsIDs);

body->getUserPointer() will point to a number, the number will represent the ID of the model, so excludeModelsIDs should include list of models ID that I want to exclude (at this point ray casting will act like they don't exists).

Edited by Medo3337, 26 November 2012 - 02:44 AM.


#6 Steve_Segreto   Crossbones+   -  Reputation: 1519

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Posted 26 November 2012 - 11:39 AM

Good luck to you! Remember, it's your job to write your code not mine :)

You can scrape out the concept of collision filters from the code snippet I already gave you or use the Bullet documentation and examples to learn more about it. Basically a collision filter is how to exclude a shape from raycasting. The example I gave you above allows you to exclude static and dynamic objects, so that you can use collision ghost objects for dynamic objects (like MOBs) and exclude one of them (like yourself) so that certain kinds of operations are simpler ... the code above was cut from code I used for movement routines.

#7 Medo3337   Members   -  Reputation: 665

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Posted 26 November 2012 - 11:59 AM

Of course it's my job to write my code, I'm asking for the parts that I don't understand yet.

I think collision filter will not work because I ONLY want to exclude certain models from ray casting and still detect collision with them, I could exclude a character/vehicle or anything mesh from ray casting even this mesh is still physical and still need to detect collision with it.

#8 Steve_Segreto   Crossbones+   -  Reputation: 1519

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Posted 26 November 2012 - 02:46 PM

Yeah sorry, that came off a bit rude - typed text always sounds on a bad note :)

The collision filter could work if you set it right before you do a raycast and then reset it to the original value right after, then you could still collide with it during your StepSimulation part. It works for me at least.

#9 Medo3337   Members   -  Reputation: 665

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Posted 26 November 2012 - 10:49 PM

Okay, thank you, I will take a look over collision filter.

If you have knowledge about Bullet Vehicle, please take a look over this thread:
http://www.gamedev.net/topic/634827-bullet-vehicle-wheels-direction-problem-code-attached/

The vehicle is working except one problem, the wheels are looking at the sides of the vehicle instead of the front direction therefore the wheels are rotating incorrectly.




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