public bool StickyPreSolve(cpArbiter arb, object data)
{
// We want to fudge the collisions a bit to allow shapes to overlap more.
// This simulates their squishy sticky surface, and more importantly
// keeps them from separating and destroying the joint.
// Track the deepest collision point and use that to determine if a rigid collision should occur.
float deepest = cp.Infinity;
// Grab the contact set and iterate over them.
cpContactPointSet contacts = arb.GetContactPointSet();
for (int i = 0; i < contacts.count; i++)
{
// Sink the contact points into the surface of each shape.
contacts.points[i].pointA = cpVect.cpvsub(contacts.points[i].pointA, cpVect.cpvmult(contacts.normal, STICK_SENSOR_THICKNESS));
contacts.points[i].pointB = cpVect.cpvadd(contacts.points[i].pointB, cpVect.cpvmult(contacts.normal, STICK_SENSOR_THICKNESS));
deepest = cp.cpfmin(deepest, contacts.points[i].distance); // + 2.0f*STICK_SENSOR_THICKNESS);
}
// Set the new contact point data.
arb.SetContactPointSet(ref contacts);
// If the shapes are overlapping enough, then create a
// joint that sticks them together at the first contact point.
if (arb.GetUserData() == null && deepest <= 0.0f)
{
cpBody bodyA, bodyB;
arb.GetBodies(out bodyA, out bodyB);
// Create a joint at the contact point to hold the body in place.
cpVect anchorA = bodyA.WorldToLocal(contacts.points[0].pointA);
cpVect anchorB = bodyB.WorldToLocal(contacts.points[0].pointB);
cpConstraint joint = new cpPivotJoint(bodyA, bodyB, anchorA, anchorB);
// Give it a finite force for the stickyness.
joint.SetMaxForce(3e3f);
// Schedule a post-step() callback to add the joint.
space.AddPostStepCallback(
(s, o1, o2) => PostStepAddJoint(joint, null),
joint, null);
// Store the joint on the arbiter so we can remove it later.
arb.SetUserData(joint);
}
// Position correction and velocity are handled separately so changing
// the overlap distance alone won't prevent the collision from occuring.
// Explicitly the collision for this frame if the shapes don't overlap using the new distance.
return(deepest <= 0.0f);
// Lots more that you could improve upon here as well:
// * Modify the joint over time to make it plastic.
// * Modify the joint in the post-step to make it conditionally plastic (like clay).
// * Track a joint for the deepest contact point instead of the first.
// * Track a joint for each contact point. (more complicated since you only get one data pointer).
}
private void Draw(cpPivotJoint constraint)
{
cpVect a = cpTransform.Point(constraint.a.transform, constraint.GetAnchorA());
cpVect b = cpTransform.Point(constraint.b.transform, constraint.GetAnchorB());
//DrawSegment(a, b, 1, cpColor.Grey);
DrawDot(a, 3, CONSTRAINT_COLOR);
DrawDot(b, 3, CONSTRAINT_COLOR);
}
//static PhysicsJointPin* ruct(PhysicsBody* a, PhysicsBody* b, cpVect anchr);
#region PROTECTED FUNC
protected bool Init(CCPhysicsBody a, CCPhysicsBody b, CCPoint anchr)
{
if (!base.Init(a, b))
{
return(false);
}
cpConstraint joint = new cpPivotJoint(GetBodyInfo(a).Body, GetBodyInfo(b).Body,
PhysicsHelper.CCPointToCpVect(anchr));
if (joint == null)
{
return(false);
}
_info.Add(joint);
return(true);
}
protected bool Init(CCPhysicsBody a, CCPhysicsBody b, CCPoint anchr)
{
if (!base.Init(a, b))
{
return(false);
}
GetBodyNode(a).Position = anchr;
GetBodyNode(b).Position = anchr;
// add a pivot joint to fixed two body together
//cpConstraint joint = cpPivotJoint.cpPivotJointNew(getBodyInfo(a).getBody(),
// getBodyInfo(b).getBody(),
// anchr);
cpConstraint joint = new cpPivotJoint(GetBodyInfo(a).Body, GetBodyInfo(b).Body, PhysicsHelper.CCPointToCpVect(anchr));
if (joint == null)
{
return(false);
}
_info.Add(joint);
// add a gear joint to make two body have the same rotation.
joint = new cpGearJoint(GetBodyInfo(a).Body, GetBodyInfo(b).Body, 0, 1);
if (joint == null)
{
return(false);
}
_info.Add(joint);
SetCollisionEnable(false);
return(true);
}
