ApplyLinearImpulse() working in one direction only

I am trying to use both b2PrismaticJoint and b2MouseJoint. I need to move my projectile along x-axis to position it for target and want to only swipe vertically without moving the projectile to throw it in that direction. I am using ApplyLinearImpulse() but no matter in which direction i swipe it's direction is always towards top-right. The code is:

- (void)ccTouchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {


   UITouch *myTouch = [touches anyObject];
   CGPoint location = [myTouch locationInView:[myTouch view]];
   location = [[CCDirector sharedDirector] convertToGL:location];
   b2Vec2 locationWorld = b2Vec2(location.x/PTM_RATIO, location.y/PTM_RATIO);

   if (_mouseJoint) {   
           _world->DestroyJoint(_mouseJoint);
           _mouseJoint = NULL;
      }
   if(_primJoint) {
          _world->DestroyJoint(_primJoint);
          _primJoint = NULL;
   }    

   if (hit) {       
    _strikerBody-开发者_如何转开发>ApplyLinearImpulse(locationWorld, _strikerBody->GetPosition());       
   }
}

Looks like your locationWorld vector is pointing in the same direction every time. I think you want something like this:

b2Vec2 impulseDirection = locationWorld - _strikerBody->GetPosition();
impulseDirection.Normalize();

const double Force = 10 * _strikerBody->GetMass(); //or anything you want
_strikerBody->ApplyLinearImpulse( Force*impulseDirection, _strikerBody->GetPosition() );

Now the impulse will be applied to the center of the _strikerBody in the touch direction (relative to the _strikerBody) .