Jump Path

[sagarsarma]

I am creating a platform jumping game where the jump path for player from Platform A to Platform B is as given in the link.
http://chipmunk-physics.net/forum/downl ... view&id=81

I have modified the oneWay platform example of Chimpmunk Engine to implement a prototype jump. The video for the outcome is provided in http://www.youtube.com/watch?v=6CA9lTfXFjg.

Question 1 : My implementation is based on application of horizontal force ( cpBodySetForce call) to the object after giving an upward velocity. To obtain the projectile path I did trial & error to determine the force vector. I need a definitive way to determine the force vector to be applied given the distance between platforms ( say A and B). Any guidance will be appreciated.

Question 2 : While the body lands on platform after the jump, it falls with any one of the 4 edges. How do I make it land on a given edge?

Code: Select all

#include <cstdio>
#include "chipmunk.h"
#include "ChipmunkDemo.h"

typedef struct OneWayPlatform {
	cpVect n; // direction objects may pass through
} OneWayPlatform;

FILE *fp;
static OneWayPlatform platformInstance;
static cpBody *body, *staticBody,*staticBody1,*staticBody2; 
static cpShape *shape;

static cpBool
preSolve(cpArbiter *arb, cpSpace *space, void *ignore)
{
	CP_ARBITER_GET_SHAPES(arb, a, b);
	OneWayPlatform *platform = (OneWayPlatform *)cpShapeGetUserData(a);
		
	if(cpvdot(cpArbiterGetNormal(arb, 0), platform->n) < 0){
		cpArbiterIgnore(arb);
		return cpFalse;
	}
	return cpTrue;
}

static void
update(cpSpace *space)
{
	static cpFloat startTime, diffTime;
	cpVect end, jump={0,0};
	int steps = 1;
	cpFloat dt = 1.0f/60.0f/(cpFloat)steps;
	
	for(int i=0; i<steps; i++){
		cpSpaceStep(space, dt);
	}

	/* execute only once while right click is pressed & initiate the jump */ 
	if (ChipmunkDemoRightClick) {
		 		end = ChipmunkDemoMouse; 
				cpVect start = cpBodyGetPos(body);
     			cpBodySetAngVel(body, 1.0f);
				cpBodySetVel(body, cpv(-98, 145));
				cpBodySetForce(body,cpv(40,0));
				}

	//if vertical velocity has reached + then make force= 0 
	jump =  cpBodyGetVel(body); 
	if ( jump.y < 0.5 && jump.y > -0.5) { 
		cpBodySetForce(body,cpv(0,0)); 
	}
 }
static cpSpace *
init(void)
{
	ChipmunkDemoMessageString = "Experiment for Jumping Distance on Mouse Click.";
	fp=fopen("logfile.txt","w"); 
	cpSpace *space = cpSpaceNew();
	cpSpaceSetIterations(space, 10);
	cpSpaceSetGravity(space, cpv(0, -75));
	
	staticBody = cpSpaceGetStaticBody(space);
	staticBody1 = cpSpaceGetStaticBody(space);
	staticBody2 = cpSpaceGetStaticBody(space);

	// Create segments around the edge of the screen.
	shape = cpSpaceAddShape(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 = cpSpaceAddShape(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 = cpSpaceAddShape(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 = cpSpaceAddShape(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 1st one way segment
//	cpBodySetPos(staticBody1, cpvmult(cpvadd(cpv(260,-100),cpv(310,-100)), 0.5));
	shape = cpSpaceAddShape(space, cpSegmentShapeNew(staticBody1, cpv(260,-100), cpv(310,-100), 5.0f));
	cpShapeSetElasticity(shape, 1.0f);
	cpShapeSetFriction(shape, 0.95f);
	cpShapeSetCollisionType(shape, 1);
	cpShapeSetLayers(shape, NOT_GRABABLE_MASK);
	
	// We'll use the data pointer for the OneWayPlatform struct
	platformInstance.n = cpv(0, 1); // let objects pass upwards
	cpShapeSetUserData(shape, &platformInstance);

	// Add our 2nd one way segment

	shape = cpSpaceAddShape(space, cpSegmentShapeNew(staticBody2, cpv(250,-200), cpv(310,-200), 5.0f));
	cpShapeSetElasticity(shape, 1.0f);
	cpShapeSetFriction(shape, 1.0f);
	cpShapeSetCollisionType(shape, 1);
	cpShapeSetLayers(shape, NOT_GRABABLE_MASK);
	
	// We'll use the data pointer for the OneWayPlatform struct
	platformInstance.n = cpv(0, 1); // let objects pass upwards
	cpShapeSetUserData(shape, &platformInstance);
	
	
	// Add a ball to make things more interesting
//	cpFloat radius = 8.0f;
//	body = cpSpaceAddBody(space, cpBodyNew(10.0f, cpMomentForCircle(10.0f, 0.0f, radius, cpvzero)));
	cpFloat mass = 0.5f;
	cpFloat moment = cpMomentForBox( mass, 20,20); 
	body = cpBodyNew(mass, moment);
	cpSpaceAddBody(space,body); 
	cpBodySetPos(body, cpv(260, -170));

	shape = cpBoxShapeNew(body, 20,20);
	cpShapeSetElasticity(shape, 0.0f);
	cpShapeSetFriction(shape, 0.9f);
	cpSpaceAddShape(space, shape);
	cpShapeSetCollisionType(shape, 2);
	
	cpSpaceAddCollisionHandler(space, 1, 2, NULL, preSolve, NULL, NULL, NULL);
	
	return space;
}

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

ChipmunkDemo OneWay = {
	"One Way Platforms",
	init,
	update,
	ChipmunkDemoDefaultDrawImpl,
	destroy,
};

jump.jpg (8.53 KiB) Viewed 3557 times

[slembcke]

So I'm not exactly certain what you are asking for, but it sounds like question one can be answered using some basic physics formulas:

distance = velocity*time + acceleration*time^2/2
acceleration = force/mass

Start with how long the object will be in the air and use the above equations to solve for time in the vertical direction. Then solve for the horizontal force. I think that's what you are after anyway.

In your second question, are you asking how to make the object not rotate? You are setting the angular velocity specifically to make it rotate. Just don't do that. Also if you give it an infinite moment of inertia, no force will be strong enough to make it rotate.

[sagarsarma]

thanks for your response.

For the 1st question, you got it right. I need sometime to figure out the implementation based on these formulae. I will take help of your player control example to get through it.

for the 2nd one, I want to rotate the sprite once during the flight path and was thinking of using the angular velocity of the box to get it. Now I am rethinking on it to achieve by other mechanism.

Thanks again.