Apply Linear Impulse to Rotation of Sprite- Cocos2d/Box2D

Question

I have an arrow and a ball. The anchorPoint for the arrow is on the bottom. All I need to do is have the sprite be able to rotate with touch, then a linear impulse is applied to the ball and shot in the direction the arrow is pointing to.

E.G.

Say you rotate the arrow 70 degrees then press the fire button. The ball is then shot in a 70 degree angle.

Currently, this is what I am using but the ball does not shoot in the direction the arrow is pointing too.

Rotates arrow with touch.

-(void)ccTouchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];

    //acquire the previous touch location
    CGPoint firstLocation = [touch previousLocationInView:[touch view]];
    CGPoint location = [touch locationInView:[touch view]];

    //preform all the same basic rig on both the current touch and previous touch
    CGPoint touchingPoint = [[CCDirector sharedDirector] convertToGL:location];
    CGPoint firstTouchingPoint = [[CCDirector sharedDirector] convertToGL:firstLocation];

    CGPoint firstVector = ccpSub(firstTouchingPoint, _arrow.position);
    CGFloat firstRotateAngle = -ccpToAngle(firstVector);
    CGFloat previousTouch = CC_RADIANS_TO_DEGREES(firstRotateAngle);

    CGPoint vector = ccpSub(touchingPoint, _arrow.position);
    CGFloat rotateAngle = -ccpToAngle(vector);
    CGFloat currentTouch = CC_RADIANS_TO_DEGREES(rotateAngle);

    //keep adding the difference of the two angles to the dial rotation
    arrowRotation += currentTouch - previousTouch;
}

Fire Button to shoot the ball in the direction the arrow is pointing too.

-(void) fireBall: (id)sender
{
    [self unscheduleUpdate];

    direction = arrowRotation;
    b2Vec2 force = b2Vec2(direction, 24.8);
    _ballBody->ApplyLinearImpulse(force, _ballBody->GetWorldCenter());
}

Any help is greatly appreciated! Thanks in advance!

James Webster James Webster · Accepted Answer · 2011-09-05T07:24:50

The impulse you are applying to the ball is (direction, 24.8). Should it not be: (direction.x * 24.8, direction.y * 24.8). This may not be the only problem, but it's one that jumped out at me.

Apply Linear Impulse to Rotation of Sprite- Cocos2d/Box2D

1 Answers