Function stickyPreSolve

src/examples/physics/physics.cpp:387–446

}

cpBool stickyPreSolve( Arbiter* arb, Space* space, void* ) {
	// 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.
	cpFloat deepest = INFINITY;

	// Grab the contact set and iterate over them.
	cpContactPointSet contacts = arb->getContactPointSet();

	for ( int i = 0; i < contacts.count; i++ ) {
		// Increase the distance (negative means overlapping) of the
		// collision to allow them to overlap more.
		// This value is used only for fixing the positions of overlapping shapes.
		cpFloat dist = contacts.points[i].dist + 2.0f * STICK_SENSOR_THICKNESS;
		contacts.points[i].dist = eemin<Float>( 0.0f, dist );
		deepest = eemin<Float>( deepest, dist );
	}

	// Set the new contact point data.
	arb->setContactPointSet( &contacts );

	// If the shapes are overlapping enough, then create a
	// joint that sticks them together at the first contact point.

	if ( !arb->getUserData() && deepest <= 0.0f ) {
		Body *bodyA, *bodyB;
		arb->getBodies( &bodyA, &bodyB );

		// Create a joint at the contact point to hold the body in place.
		PivotJoint* joint =
			eeNew( PivotJoint, ( bodyA, bodyB, tovect( contacts.points[0].point ) ) );

		// Dont draw the constraint
		joint->setDrawPointSize( 0 );

		// Give it a finite force for the stickiness.
		joint->setMaxForce( 3e3 );

		// Schedule a post-step() callback to add the joint.
		space->addPostStepCallback( &postStepAddJoint, 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 occurring.
	// 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