// Create a constraint between me (root of linkset) and the passed prim (the child).
// Called at taint time!
private void PhysicallyLinkAChildToRoot(BSPhysObject rootPrim, BulletBody rootBody,
BSPhysObject childPrim, BulletBody childBody)
{
// Zero motion for children so they don't interpolate
childPrim.ZeroMotion();
// Relative position normalized to the root prim
// Essentually a vector pointing from center of rootPrim to center of childPrim
OMV.Vector3 childRelativePosition = childPrim.Position - rootPrim.Position;
// real world coordinate of midpoint between the two objects
OMV.Vector3 midPoint = rootPrim.Position + (childRelativePosition / 2);
DetailLog("{0},PhysicallyLinkAChildToRoot,taint,root={1},rBody={2},child={3},cBody={4},rLoc={5},cLoc={6},midLoc={7}",
rootPrim.LocalID,
rootPrim.LocalID, rootBody.ptr.ToString("X"),
childPrim.LocalID, childBody.ptr.ToString("X"),
rootPrim.Position, childPrim.Position, midPoint);
// create a constraint that allows no freedom of movement between the two objects
// http://bulletphysics.org/Bullet/phpBB3/viewtopic.php?t=4818
// There is great subtlty in these paramters. Notice the check for a ptr of zero.
// We pass the BulletBody structure into the taint in order to capture the pointer
// of the body at the time of constraint creation. This doesn't work for the very first
// construction because there is no body yet. The body
// is constructed later at taint time. Thus we use the body address at time of the
// taint creation but, if it is zero, use what's in the prim at the moment.
// There is a possible race condition since shape can change without a taint call
// (like changing to a mesh that is already constructed). The fix for that would be
// to only change BSShape at taint time thus syncronizing these operations at
// the cost of efficiency and lag.
BS6DofConstraint constrain = new BS6DofConstraint(
PhysicsScene.World,
rootBody.ptr == IntPtr.Zero ? rootPrim.BSBody : rootBody,
childBody.ptr == IntPtr.Zero ? childPrim.BSBody : childBody,
midPoint,
true,
true
);
/* NOTE: below is an attempt to build constraint with full frame computation, etc.
* Using the midpoint is easier since it lets the Bullet code manipulate the transforms
* of the objects.
* Code left as a warning to future programmers.
* // ==================================================================================
* // relative position normalized to the root prim
* OMV.Quaternion invThisOrientation = OMV.Quaternion.Inverse(rootPrim.Orientation);
* OMV.Vector3 childRelativePosition = (childPrim.Position - rootPrim.Position) * invThisOrientation;
*
* // relative rotation of the child to the parent
* OMV.Quaternion childRelativeRotation = invThisOrientation * childPrim.Orientation;
* OMV.Quaternion inverseChildRelativeRotation = OMV.Quaternion.Inverse(childRelativeRotation);
*
* // create a constraint that allows no freedom of movement between the two objects
* // http://bulletphysics.org/Bullet/phpBB3/viewtopic.php?t=4818
* DetailLog("{0},PhysicallyLinkAChildToRoot,taint,root={1},child={2}", rootPrim.LocalID, rootPrim.LocalID, childPrim.LocalID);
* BS6DofConstraint constrain = new BS6DofConstraint(
* PhysicsScene.World, rootPrim.Body, childPrim.Body,
* OMV.Vector3.Zero,
* OMV.Quaternion.Inverse(rootPrim.Orientation),
* OMV.Vector3.Zero,
* OMV.Quaternion.Inverse(childPrim.Orientation),
* // A point half way between the parent and child
* // childRelativePosition/2,
* // childRelativeRotation,
* // childRelativePosition/2,
* // inverseChildRelativeRotation,
* true,
* true
* );
* // ==================================================================================
*/
PhysicsScene.Constraints.AddConstraint(constrain);
// zero linear and angular limits makes the objects unable to move in relation to each other
constrain.SetLinearLimits(OMV.Vector3.Zero, OMV.Vector3.Zero);
constrain.SetAngularLimits(OMV.Vector3.Zero, OMV.Vector3.Zero);
// tweek the constraint to increase stability
constrain.UseFrameOffset(PhysicsScene.BoolNumeric(PhysicsScene.Params.linkConstraintUseFrameOffset));
constrain.TranslationalLimitMotor(PhysicsScene.BoolNumeric(PhysicsScene.Params.linkConstraintEnableTransMotor),
PhysicsScene.Params.linkConstraintTransMotorMaxVel,
PhysicsScene.Params.linkConstraintTransMotorMaxForce);
constrain.SetCFMAndERP(PhysicsScene.Params.linkConstraintCFM, PhysicsScene.Params.linkConstraintERP);
if (PhysicsScene.Params.linkConstraintSolverIterations != 0f)
{
constrain.SetSolverIterations(PhysicsScene.Params.linkConstraintSolverIterations);
}
RecomputeLinksetConstraintVariables();
}