/* 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.h" #include "ChipmunkDemo.h" enum { COLLIDE_STICK_SENSOR = 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++){ // Increase the distance (negative means overlaping) 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 = cpfmin(0.0f, dist); deepest = cpfmin(deepest, dist); } // 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. cpConstraint *joint = cpPivotJointNew(bodyA, bodyB, contacts.points[0].point); // 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) { int steps = 1; cpFloat dt = 1.0f/60.0f/(cpFloat)steps; for(int i=0; i<steps; i++){ 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); cpShapeSetCollisionType(shape, COLLIDE_STICK_SENSOR); cpShapeSetLayers(shape, NOT_GRABABLE_MASK); shape = cpSpaceAddShape(space, cpSegmentShapeNew(staticBody, cpv( 340,-260), cpv( 340, 260), 20.0f)); cpShapeSetElasticity(shape, 1.0f); cpShapeSetFriction(shape, 1.0f); cpShapeSetCollisionType(shape, COLLIDE_STICK_SENSOR); cpShapeSetLayers(shape, NOT_GRABABLE_MASK); shape = cpSpaceAddShape(space, cpSegmentShapeNew(staticBody, cpv(-340,-260), cpv( 340,-260), 20.0f)); cpShapeSetElasticity(shape, 1.0f); cpShapeSetFriction(shape, 1.0f); cpShapeSetCollisionType(shape, COLLIDE_STICK_SENSOR); cpShapeSetLayers(shape, NOT_GRABABLE_MASK); shape = cpSpaceAddShape(space, cpSegmentShapeNew(staticBody, cpv(-340, 260), cpv( 340, 260), 20.0f)); cpShapeSetElasticity(shape, 1.0f); cpShapeSetFriction(shape, 1.0f); cpShapeSetCollisionType(shape, COLLIDE_STICK_SENSOR); cpShapeSetLayers(shape, NOT_GRABABLE_MASK); 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))); cpBodySetPos(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, COLLIDE_STICK_SENSOR); } cpSpaceAddCollisionHandler(space, COLLIDE_STICK_SENSOR, COLLIDE_STICK_SENSOR, NULL, StickyPreSolve, NULL, StickySeparate, NULL); return space; } static void destroy(cpSpace *space) { ChipmunkDemoFreeSpaceChildren(space); cpSpaceFree(space); } ChipmunkDemo Sticky = { "Sticky Surfaces", init, update, ChipmunkDemoDefaultDrawImpl, destroy, };