Real-Time Physics Simulation Forum

My program was using v2.81, and I recently upgraded to v2.82. My rayTest calls are producing some very wacky behavior. What was changed with the rayTest between v2.81 and v2.82?

Specifically, I'm performing a ray test against a btBvhTriangleMesh.

Yes, exactly the same timestep. A lot of times the m_partId* and m_index* will return 0 instead of the uninitialized -8655302 (whatever). Even if I change the bullet code to initialize these variables to -1, it will still return bogus 0 values. I have had to hardcode to ignore index 0 and pad out my...

Turns out masks aren't all you have to do... I get fewer manifolds if I also toss out the collision if both objects have a linear velocity of zero. I'm surprised that bullet doesn't do this automatically for CF_NO_CONTACT_RESPONSE objects, but maybe there's a good reason...?

I have a world with a LOT of collectible items (think like coins in Mario). What's the best way of representing these in bullet's world? Right now they are spheres with CF_NO_CONTACT_RESPONSE, but they still seem to be generating a lot of unnecessary manifolds and contact points, even when I am not ...

I have a rigid body that is riding an elevator, slowly rising. I've tried creating the elevator out of btBvhTriangleMeshShape, btConvexShape, btBoxShape, and all have the same behavior -- as the elevator slowly rises, the rigid body on top (btSphereShape), jitters up and down. What is causing this a...

My program runs on both Win32/x86 and iOS/ARM. I am getting different collision results from both - the Win32/x86 seems to be more reliable. On iOS/ARM, Sometimes my sphere will stop on the edge of a cliff on a btBvhTriangleMesh, and the wrong m_index for the contact point's polygon index will be re...

Just set the gravity to each of your objects every tic like so:

objectGravity = normalize(planetCentroid - objectPosition) * gravityStrength

The issue was that the files were added as 'blue folders' when I dragged & dropped them - I guess in this sense, XCode treats them like resources and doesn't compile them. I had to manually create yellow 'Group' folders and add the files individually to each. Now it works!

I want to build bullet directly into my project, not as a 'framework'. On Visual Studio 2010, I just had to copy the relevant sources files and everything worked dandy. Doing the same in XCode gives me trouble when I reach the linker stage: Undefined symbols for architecture armv7: "btCollision...

You need to also call ->activate()

There's also a way to disable it from going to sleep altogether. setActivationFlags? It escapes me ATM..

I want to do an ad-hoc query for collision objects that are X distance away from a btVector3 point. What's the best way to go about doing this?

You will probably need to make your btGhostObject a btRigidBody to get what you want. Or you could do something kludgy and perhaps shoot a ray downwards from your btGhostObject every tick, get the moving object's getLinearVelocity(), and do btGhostObject.setLinearVelocity() with the result... howeve...

Then related to bullet (or any physics library) would a kinematic object mean moved by keys, joystick, simply time or whatever you want to, a force by the physics library (which needs to be implemented ofcourse). As function like colObj.collidesWith (or something like that) how does a kinematic obj...

In my post-tick callback, I evaluate the contact points and perform different actions. One of these actions is that I want to change, essentially 'teleport' the btRigidBody. But I have an eerie feeling it's not a good idea to be adding & removing objects from the dynamicsWorld until the entire s...

btCollisionObject is the parent class of btRigidBody. So a btCollisionObject could be a Rigid Body, a Soft Body, or Kinematic body. I would suggest keeping track of btCollisionObject pointers and upcasting to btRigidBody when needed. Then it would be easier to add things like soft bodies to your app...