Bullet Wrapper Custom classes - s76/libgdx GitHub Wiki

In some cases it's not possible to wrap a C++ bullet class/method in a Java class/method, in which case a custom class or method is used to bridge the two. The following list describes those. Note that the list might not be complete.

The btCollisionObject is modified to reuse Java objects instead of creating a new Java object every time. This is done using the static btCollisionObject.instances map. To remove an object from the map and delete the native object use the dispose method.

Besides reusing instances, the Bullet wrappers allows you to provide a unique number to identify the instance. For example the index/ID of the entity in your entity system. Some frequently called methods allow you to use that value instead of the instance itself. This completely eliminates the overhead of mapping C++ and Java instances. You can set this value using the setUserValue(int); method and retrieve the value using the getUserValue(); method.

public class MyGameObject {
  public btCollisionObject body;
}
...
Array<MyGameObject> gameObjects;
...
gameObjects.add(myGameObject);
myGameObject.setUserValue(gameObjects.size-1);

You can use the userData field to add some additional data. For example:

btCollisionObject obj = new btCollisionObject();
obj.userData = myGameObject;
...
if (obj.userData instanceof MyGameObject)
  myGameObject = (MyGameObject)obj.userData;

btCollisionObject adds the methods takeOwnership and releaseOwnership which can be used to remove or make the wrapper responsable for destroying the native object when the Java object is destroyed by the garbage collector.

The btCollisionObject also adds the following methods:

• getAnisotropicFriction(Vector3)
• getWorldTransform(Matrix4)
• getInterpolationWorldTransform(Matrix4)
• getInterpolationLinearVelocity(Vector3)
• getInterpolationAngularVelocity(Vector3)
• getContactCallbackFlag() and setContactCallbackFlag(int)
• getContactCallbackFilter() and setContactCallbackFilter(int)

The ClosestNotMeConvexResultCallback class is a custom ClosestConvexResultCallback implementation which you can use to perform a convexSweepTest on all objects except the specified one.

The ClosestNotMeRayResultCallback class is a custom ClosestRayResultCallback implementation which you can use to perform a rayTest on all objects except the specified one.

The InternalTickCallback is implemented to bridge the callback required by btDynamicsWorld#setInternalTickCallback to a java class. You can extend the class and override onInternalTick method. You can use the attach and detach methods to start and stop getting tick callbacks.

In some cases it's easier to use btDefaultMotionState instead of extending btMotionState. The following custom methods are available for btDefaultMotionState.

• getGraphicsWorldTrans(Matrix4)
• getCenterOfMassOffset(Matrix4)
• getStartWorldTrans(Matrix4) Note that extending btMotionState with your own implementation is the preferred method.

The btCompoundShape class allows to keep a reference to child shapes, so you don't have to do that. To use it, use the addChildShape with the third managed argument set to true. Note that this will delete the managed child shape if the compound shape is deleted. Therefor the managed shapes should be exclusive for the compound shape.

The btIndexedMesh class adds the constructor:

• btIndexedMesh(Mesh) And the methods:
• setTriangleIndexBase(ShortBuffer)
• setVertexBase(FloatBuffer)
• set(Mesh) For easy constructing or setting a btIndexedMesh based on a Mesh instance or a vertex and index buffer. The buffers itself are not managed by the wrapper and should out-live the object.

The btTriangleIndexVertexArray class adds the ability to maintain a reference to the Java btIndexedMesh classes it holds. To use it call addIndexedMesh with the last argument managed set to true. When the btTriangleIndexVertexArray is destroyed it will also destroy it's managed btIndexedMesh children.

Also, the btTriangleIndexVertexArray class adds the addMesh and addModel methods and likewise constructors, for easy constructing and setting the class.

The btBvhTriangleMeshShape class adds the ability to maintain a reference to the Java btStridingMeshInterface class. To use it construct the class with the argument managed set to true. When the btBvhTriangleMeshShape is destroyed it will also destroy the managed btStridingMeshInterface.

Also, the btBvhTriangleMeshShape class add constructors for easy constructing one or more Mesh or Model instances.

The btConvexHullShape class adds a convenience constructor btConvexHullShape(btShapeHull).

The btBroadphasePairArray class adds methods to get all collision objects within it at once:

btBroadphasePairArray.getCollisionObjects(Array<btCollisionObject> out, btCollisionObject other, int[] tempArray)
btBroadphasePairArray.getCollisionObjectsValue(int[] out, btCollisionObject other)