axmol/tests/cpp-tests/Source/ChipmunkTestBed/demo/Sticky.cpp

/* Copyright (c) 2007 Scott Lembcke
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include "chipmunk/chipmunk.h"
#include "ChipmunkDemo.h"

enum
{
    COLLISION_TYPE_STICKY = 1,
};

#define STICK_SENSOR_THICKNESS 2.5f

static void PostStepAddJoint(cpSpace* space, void* key, void* data)
{
    //	printf("Adding joint for %p\n", data);

    cpConstraint* joint = (cpConstraint*)key;
    cpSpaceAddConstraint(space, joint);
}

static cpBool StickyPreSolve(cpArbiter* arb, cpSpace* space, void* 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.
    cpFloat deepest = INFINITY;

    // Grab the contact set and iterate over them.
    cpContactPointSet contacts = cpArbiterGetContactPointSet(arb);
    for (int i = 0; i < contacts.count; i++)
    {
        // Sink the contact points into the surface of each shape.
        contacts.points[i].pointA = cpvsub(contacts.points[i].pointA, cpvmult(contacts.normal, STICK_SENSOR_THICKNESS));
        contacts.points[i].pointB = cpvadd(contacts.points[i].pointB, cpvmult(contacts.normal, STICK_SENSOR_THICKNESS));
        deepest                   = cpfmin(deepest, contacts.points[i].distance);  // + 2.0f*STICK_SENSOR_THICKNESS);
    }

    // Set the new contact point data.
    cpArbiterSetContactPointSet(arb, &contacts);

    // If the shapes are overlapping enough, then create a
    // joint that sticks them together at the first contact point.
    if (!cpArbiterGetUserData(arb) && deepest <= 0.0f)
    {
        CP_ARBITER_GET_BODIES(arb, bodyA, bodyB);

        // Create a joint at the contact point to hold the body in place.
        cpVect anchorA      = cpBodyWorldToLocal(bodyA, contacts.points[0].pointA);
        cpVect anchorB      = cpBodyWorldToLocal(bodyB, contacts.points[0].pointB);
        cpConstraint* joint = cpPivotJointNew2(bodyA, bodyB, anchorA, anchorB);

        // Give it a finite force for the stickyness.
        cpConstraintSetMaxForce(joint, 3e3);

        // Schedule a post-step() callback to add the joint.
        cpSpaceAddPostStepCallback(space, PostStepAddJoint, joint, NULL);

        // Store the joint on the arbiter so we can remove it later.
        cpArbiterSetUserData(arb, 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).
}

static void PostStepRemoveJoint(cpSpace* space, void* key, void* data)
{
    //	printf("Removing joint for %p\n", data);

    cpConstraint* joint = (cpConstraint*)key;
    cpSpaceRemoveConstraint(space, joint);
    cpConstraintFree(joint);
}

static void StickySeparate(cpArbiter* arb, cpSpace* space, void* data)
{
    cpConstraint* joint = (cpConstraint*)cpArbiterGetUserData(arb);

    if (joint)
    {
        // The joint won't be removed until the step is done.
        // Need to disable it so that it won't apply itself.
        // Setting the force to 0 will do just that
        cpConstraintSetMaxForce(joint, 0.0f);

        // Perform the removal in a post-step() callback.
        cpSpaceAddPostStepCallback(space, PostStepRemoveJoint, joint, NULL);

        // NULL out the reference to the joint.
        // Not required, but it's a good practice.
        cpArbiterSetUserData(arb, NULL);
    }
}

static void update(cpSpace* space, double dt)
{
    cpSpaceStep(space, dt);
}

static cpSpace* init(void)
{
    ChipmunkDemoMessageString = "Sticky collisions using the cpArbiter data pointer.";

    cpSpace* space = cpSpaceNew();
    cpSpaceSetIterations(space, 10);
    cpSpaceSetGravity(space, cpv(0, -1000));
    cpSpaceSetCollisionSlop(space, 2.0);

    cpBody* staticBody = cpSpaceGetStaticBody(space);
    cpShape* shape;

    // Create segments around the edge of the screen.
    shape = cpSpaceAddShape(space, cpSegmentShapeNew(staticBody, cpv(-340, -260), cpv(-340, 260), 20.0f));
    cpShapeSetElasticity(shape, 1.0f);
    cpShapeSetFriction(shape, 1.0f);
    cpShapeSetFilter(shape, NOT_GRABBABLE_FILTER);

    shape = cpSpaceAddShape(space, cpSegmentShapeNew(staticBody, cpv(340, -260), cpv(340, 260), 20.0f));
    cpShapeSetElasticity(shape, 1.0f);
    cpShapeSetFriction(shape, 1.0f);
    cpShapeSetFilter(shape, NOT_GRABBABLE_FILTER);

    shape = cpSpaceAddShape(space, cpSegmentShapeNew(staticBody, cpv(-340, -260), cpv(340, -260), 20.0f));
    cpShapeSetElasticity(shape, 1.0f);
    cpShapeSetFriction(shape, 1.0f);
    cpShapeSetFilter(shape, NOT_GRABBABLE_FILTER);

    shape = cpSpaceAddShape(space, cpSegmentShapeNew(staticBody, cpv(-340, 260), cpv(340, 260), 20.0f));
    cpShapeSetElasticity(shape, 1.0f);
    cpShapeSetFriction(shape, 1.0f);
    cpShapeSetFilter(shape, NOT_GRABBABLE_FILTER);

    for (int i = 0; i < 200; i++)
    {
        cpFloat mass   = 0.15f;
        cpFloat radius = 10.0f;

        cpBody* body = cpSpaceAddBody(space, cpBodyNew(mass, cpMomentForCircle(mass, 0.0f, radius, cpvzero)));
        cpBodySetPosition(body, cpv(cpflerp(-150.0f, 150.0f, frand()), cpflerp(-150.0f, 150.0f, frand())));

        cpShape* shape = cpSpaceAddShape(space, cpCircleShapeNew(body, radius + STICK_SENSOR_THICKNESS, cpvzero));
        cpShapeSetFriction(shape, 0.9f);
        cpShapeSetCollisionType(shape, COLLISION_TYPE_STICKY);
    }

    cpCollisionHandler* handler = cpSpaceAddWildcardHandler(space, COLLISION_TYPE_STICKY);
    handler->preSolveFunc       = StickyPreSolve;
    handler->separateFunc       = StickySeparate;

    return space;
}

static void destroy(cpSpace* space)
{
    ChipmunkDemoFreeSpaceChildren(space);
    cpSpaceFree(space);
}

ChipmunkDemo Sticky = {
    "Sticky Surfaces", 1.0 / 60.0, init, update, ChipmunkDemoDefaultDrawImpl, destroy,
};