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Editorial Team
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Asked: 2026-05-27T20:54:06+00:00

In my game every 2 seconds I create a new body and then I

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In my game every 2 seconds I create a new body and then I apply an impulse to this Box2d body.

My problem is that impulse is still the same, but the body behaves in two ways:

It slowly goes upwards , or another time it quickly falls down

I want the body to behave in the same way after impulse, is it possible?

Code:

- (void)newBullet
{
CGPoint touchedAt;
touchedAt.x = 184;
touchedAt.y = 1200;
bullet = [CCSprite spriteWithSpriteSheet:spriteSheet  rect:CGRectMake(586, 719, 32, 32)];
[spriteSheet addChild: bullet z: 10 tag: 8];

bullet.position = ccp( touchedAt.x , touchedAt.y);
bullet.rotation = 90;
bulletBodyDef.type = b2_dynamicBody;
bulletBodyDef.position.Set(touchedAt.x / PTM_RATIO, touchedAt.y / PTM_RATIO);
bulletBodyDef.userData = bullet;
bulletBodyDef.angle = CC_DEGREES_TO_RADIANS( 90 );
bulletBody = _world->CreateBody(&bulletBodyDef);

b2CircleShape bulletShape;
bulletShape.m_radius = bullet.contentSize.width/PTM_RATIO/2;

b2FixtureDef bulletShapeDef;
bulletShapeDef.shape = &bulletShape;
bulletShapeDef.density = 0.0f;
bulletShapeDef.friction = 0.9f;
bulletShapeDef.restitution = 0.0f;
bulletShapeDef.isSensor = false;
bulletFixture = bulletBody->CreateFixture(&bulletShapeDef);

b2Vec2 force = b2Vec2(6.0f, 4.0f );
bulletBody->ApplyImpulse(force, bulletBody->GetPosition());
}

Video(Sorry for poor quality, but you can see what I mean)
http://vimeo.com/34215327

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1 Answer

  1. Editorial Team

    I don’t know how you are calling this method, but I suggest that you have more control over where you call the method and where you do the box2d time step, it might not be related to that, but its worth checking out. What might be happening is that the impulse is not being applied because the solver which determines the speed of the body isn’t called until you reset forces (which I assume you are doing), and so the effect is lost.

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