Character Jump using Box2D - iphone

Question

I am using box2d and cocos2d for my jump based game. I need to jump the character on platforms as they come.
Any ideas of how to do it using box2d ?

Answer 1

You try this:
//OBSTACLE_1:
{
CCSprite *sprite = [CCSprite spriteWithFile:#"hungObstacle1_C2H18.png"];
sprite.position = ccp(1568,704);
sprite.tag = 4;
[self addChild:sprite];
//SHAPE :
{
b2BodyDef bodyDefinition;
bodyDefinition.type = b2_dynamicBody;
bodyDefinition.position.Set(1568/PTM_RATIO, 704/PTM_RATIO);
bodyDefinition.userData = sprite;
body = world->CreateBody(&bodyDefinition);//body is a b2Body
// Create body shape
b2PolygonShape bodyShape;
//row 1, col 1
int num = 8;
b2Vec2 verts[] = {
b2Vec2(14.5f / PTM_RATIO, -27.0f / PTM_RATIO),
b2Vec2(19.5f / PTM_RATIO, -11.0f / PTM_RATIO),
b2Vec2(19.5f / PTM_RATIO, 11.0f / PTM_RATIO),
b2Vec2(16.5f / PTM_RATIO, 24.0f / PTM_RATIO),
b2Vec2(-14.5f / PTM_RATIO, 24.0f / PTM_RATIO),
b2Vec2(-19.5f / PTM_RATIO, 16.0f / PTM_RATIO),
b2Vec2(-19.5f / PTM_RATIO, -13.0f / PTM_RATIO),
b2Vec2(-12.5f / PTM_RATIO, -26.0f / PTM_RATIO)
};
bodyShape.Set(verts, num);
// Create shape definition and add to body
b2FixtureDef bodyFixtureDefinition;
bodyFixtureDefinition.shape = &bodyShape;
bodyFixtureDefinition.density = 5000.0f;
bodyFixtureDefinition.friction = 1.0f;
bodyFixtureDefinition.restitution = 1.0f;//*
fixture=body->CreateFixture(&bodyFixtureDefinition);
}
}
*NOTE:by setting restitution to 1 body will keep jumping all the time just need little force

Answer 2

To simulate jumping, you can use the cpBodyApplyImpulse method and apply a force in a straight up direction. Assuming you've got gravity enabled, this should provide an accuracte simulation, although you may need to tweak it. For example, here is a line from a recent project of mine.
cpBodyApplyImpulse(charBody, cpv(0.0, -25 * scale), charBody->p);
This is making the sprite represented by the charBody jump.