text: /* 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 <stdlib.h>
  #include <stdio.h>
  #include <math.h>
  
  #include "chipmunk.h"
  #include "drawSpace.h"
  #include "ChipmunkDemo.h"
  
  static cpSpace *space;
  static cpBody *staticBody;
  
  typedef struct OneWayPlatform {
  	cpVect n; // direction objects may pass through
  	cpArray *passThruList; // list of objects passing through
  } OneWayPlatform;
  
  static OneWayPlatform platformInstance;
  
  static int
  preSolve(cpArbiter *arb, cpSpace *space, void *ignore)
  {
  	CP_ARBITER_GET_SHAPES(arb, a, b);
  	OneWayPlatform *platform = (OneWayPlatform*)(a->data);
  	
  	if(cpArrayContains(platform->passThruList, b)){
  		// The object is in the pass thru list, ignore it until separates.
  		return 0;
  	} else {
  		cpFloat dot = cpvdot(cpArbiterGetNormal(arb, 0), platform->n);
  		
  		if(dot < 0){
  			// Add the object to the pass thrru list
  			cpArrayPush(platform->passThruList, b);
  			return 0;
  		} else {
  			return 1;
  		}
  	}
  }
  
  static void
  separate(cpArbiter *arb, cpSpace *space, void *ignore)
  {
  	CP_ARBITER_GET_SHAPES(arb, a, b);
  	
  	// remove the object from the pass thru list
  	cpArrayDeleteObj(((OneWayPlatform *)a->data)->passThruList, b);
  }
  
  static void
  update(int ticks)
  {
  	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)
  {
  	staticBody = cpBodyNew(INFINITY, INFINITY);
  	
  	cpResetShapeIdCounter();
  	
  	space = cpSpaceNew();
  	space->iterations = 10;
  	space->gravity = cpv(0, -100);
  	
  	cpBody *body;
  	cpShape *shape;
  	
  	// Create segments around the edge of the screen.
  	shape = cpSpaceAddStaticShape(space, cpSegmentShapeNew(staticBody, cpv(-320,-240), cpv(-320,240), 0.0f));
  	shape->e = 1.0f; shape->u = 1.0f;
  	shape->layers = NOT_GRABABLE_MASK;
  
  	shape = cpSpaceAddStaticShape(space, cpSegmentShapeNew(staticBody, cpv(320,-240), cpv(320,240), 0.0f));
  	shape->e = 1.0f; shape->u = 1.0f;
  	shape->layers = NOT_GRABABLE_MASK;
  
  	shape = cpSpaceAddStaticShape(space, cpSegmentShapeNew(staticBody, cpv(-320,-240), cpv(320,-240), 0.0f));
  	shape->e = 1.0f; shape->u = 1.0f;
  	shape->layers = NOT_GRABABLE_MASK;
  	
  	// Add our one way segment
  	shape = cpSpaceAddStaticShape(space, cpSegmentShapeNew(staticBody, cpv(-160,-100), cpv(160,-100), 10.0f));
  	shape->e = 1.0f; shape->u = 1.0f;
  	shape->collision_type = 1;
  	shape->layers = NOT_GRABABLE_MASK;
  	
  	// We'll use the data pointer for the OneWayPlatform struct
  	platformInstance.n = cpv(0, 1); // let objects pass upwards
  	platformInstance.passThruList = cpArrayNew(0);
  	shape->data = &platformInstance;
  	
  	
  	// Add a ball to make things more interesting
  	cpFloat radius = 15.0f;
  	body = cpSpaceAddBody(space, cpBodyNew(10.0f, cpMomentForCircle(10.0f, 0.0f, radius, cpvzero)));
  	body->p = cpv(0, -200);
  	body->v = cpv(0, 170);
  
  	shape = cpSpaceAddShape(space, cpCircleShapeNew(body, radius, cpvzero));
  	shape->e = 0.0f; shape->u = 0.9f;
  	shape->collision_type = 2;
  	
  	cpSpaceAddCollisionHandler(space, 1, 2, NULL, preSolve, NULL, separate, NULL);
  	
  	return space;
  }
  
  static void
  destroy(void)
  {
  	cpBodyFree(staticBody);
  	cpSpaceFreeChildren(space);
  	cpSpaceFree(space);
  	
  	cpArrayFree(platformInstance.passThruList);
  }
  
  chipmunkDemo OneWay = {
  	"One Way Platforms",
  	NULL,
  	init,
  	update,
  	destroy,
  };
  