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Bullet physics mass center and weird object reaction


Bullet physics mass center and weird object reaction

By : abhikpma
Date : November 22 2020, 10:38 AM
it should still fix some issue This will be caused by your model having it's pivot point / transform origin at or near the base of the bowling pin. In Bullet the rigid body transform is the center of mass, so what you are seeing is the heavy center of mass correcting itself with gravity and thus pulling the pin upright.
You have a couple of options:
code :


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Bullet physics engine, how to freeze an object?

Bullet physics engine, how to freeze an object?


By : user2055309
Date : March 29 2020, 07:55 AM
Any of those help The documentation is a bit lacking but one would assume that the method below could be used to disable gravity on a specific body:
code :
void btRigidBody::setGravity(const btVector3 &acceleration)
apply force to an object in specefic direction with bullet physics

apply force to an object in specefic direction with bullet physics


By : Maria Eduarda duda
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , I'm trying to fire cubes from the camera origin, using the cameras direction as the firing line. I would like to be able to alter the amount of power delivered in the shot with an int. , This is how it works for me:
code :
float force = 10.0f;   //but any value that works for you
Vector3 dir = normalize(cam.origin + cam.direction) * force; //suppose your camera moves around
body->applyCentralImpulse(dir);
Box2D Farseer Physics Center of Mass and origin inconsistent

Box2D Farseer Physics Center of Mass and origin inconsistent


By : Anahit Tosunyan
Date : March 29 2020, 07:55 AM
I wish this helpful for you You can have the pivot and mass center correctly set if you create your compound polygon from a list of points relative to the center.
For a 20 units side square : instead of : [0,0][20,0][20,20][-20,20] use : [-10,-10][10,-10][10,10][-10,10]
Good way to start playing sound when two object collide in Bullet Physics

Good way to start playing sound when two object collide in Bullet Physics


By : Pattanapong Suwan
Date : March 29 2020, 07:55 AM
it fixes the issue Ok, so I found one way to do what I was looking for but it seems very unoptimized and kinda hacky. I am still wondering if there is an easy way to do this that I am not seeing. Here is what I did for now. I keep a list of persistent collisions and compare it to another list of current collisions. If current collisions have an entry that does not exist in persistent collision list, I add that to persistent ones and I play a sound. After that, I iterate over persistent collision list and remove all entries that are not contained in current collision list. Here is the code.
code :
// persistentCollisions map.
std::map<int, std::vector<int>> persistentCollisions;

// Main game loop
while (!glfwWindowShouldClose(window.getWindow()))
{
    //.
    //.
    //.

    physicsEngine->getDynamicsWorld()->stepSimulation(1.0f / 60.0f);

    // New collision map
    std::map<int, std::vector<int>> newCollisions;

    // Go over the collision manifold and extract all existing collisions
    int numManifolds = physicsEngine->getDynamicsWorld()->getDispatcher()->getNumManifolds();
    for (int i = 0; i < numManifolds; i++)
    {
        btPersistentManifold* contactManifold = physicsEngine->getDynamicsWorld()->getDispatcher()->getManifoldByIndexInternal(i);
        const btCollisionObject* obA = contactManifold->getBody0();
        const btCollisionObject* obB = contactManifold->getBody1();

        int numContacts = contactManifold->getNumContacts();
        for (int j = 0; j < numContacts; j++)
        {
            btManifoldPoint& pt = contactManifold->getContactPoint(j);
            if (pt.getDistance() < 0.f)
            {
                // If it is a new collision, add to the newCollision list
                if (std::find(newCollisions[obA->getUserIndex()].begin(), newCollisions[obA->getUserIndex()].end(), obB->getUserIndex()) == newCollisions[obA->getUserIndex()].end()) 
                {
                    newCollisions[obA->getUserIndex()].emplace_back(obB->getUserIndex());
                }
            }
        }
    }


    // Iterate over new collisions and add new collision to persistent collisions if it does not exist
    std::map<int, std::vector<int>>::iterator newCollisionIterator = newCollisions.begin();
    while (newCollisionIterator != newCollisions.end())
    {
        for (auto item : newCollisionIterator->second)
        {
            if (std::find(persistentCollisions[newCollisionIterator->first].begin(), persistentCollisions[newCollisionIterator->first].end(), item) == persistentCollisions[newCollisionIterator->first].end()) 
            {
                std::cout << "New collision between " << newCollisionIterator->first << " And " << item << std::endl;
                // We can play our collision audio here
                persistentCollisions[newCollisionIterator->first].emplace_back(item);
            }
        }

        newCollisionIterator++;
    }

    // Iterate over persistent collisions and remove all collisions that did not exist in new collision
    std::map<int, std::vector<int>>::iterator persistentCollisionIterator = persistentCollisions.begin();
    while (persistentCollisionIterator != persistentCollisions.end())
    {
        std::vector<int>::iterator iter;
        for (iter = persistentCollisionIterator->second.begin(); iter != persistentCollisionIterator->second.end(); ) 
        {
            if (std::find(newCollisions[persistentCollisionIterator->first].begin(), newCollisions[persistentCollisionIterator->first].end(), *iter) != newCollisions[persistentCollisionIterator->first].end())
            {
                ++iter;
            }
            else
            {
                iter = persistentCollisionIterator->second.erase(iter);
            }
        }

        persistentCollisionIterator++;
    }
}
corona physics - different mass object?

corona physics - different mass object?


By : defacid
Date : March 29 2020, 07:55 AM
I wish this help you
and i'm trying to change the mass of those ball, so the ball that higher from the ground can drop faster
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