Linear Impulses - Cocos2d/Objective-C/Box2d - iphone

Question

I have a cannon, a ball, and a trigger. When you press the trigger a linear impulse is applied to the ball.
short int direction = [level.cannon cannon].rotation;
short int power = 24.8;
b2Vec2 force = b2Vec2(direction, power);
[level.ball body]->ApplyLinearImpulse(force, [level.ball body]->GetWorldCenter());
My problem is, when the trigger is pressed, the linear impulse is applied to the ball, but the ball doesn't actually come out of the top of the cannon sprite.
The reason it is doing this (I think) is because I have set the anchor point, for the cannon, to (0.5, 0).
cannon.anchorPoint = ccp(0.5, 0);
I have figured out that for every 5 degrees the cannon rotates, a multiple of 2 needs to be added/subtracted to the rotation.
E.G.
For 0 to 55 Degrees
0 to 5 subtract 2 from the rotation
5 to 10 subtract 4 from the rotation
10 to 15 subtract 6 from the rotation
etc.
For 0 to -55 Degrees
0 to -5 add 2 to the rotation
-5 to -10 add 4 to the rotation
-10 to -15 add 6 to the rotation
Currently, I am using this code to accomplish this.
if (_cannon.rotation == 0)
{
direction = _cannon.rotation;
} else if (_cannon.rotation >= 1 && _cannon.rotation < 6)
{
direction = _cannon.rotation - 2;
} else if (_cannon.rotation >= 6 && _cannon.rotation < 11)
{
direction = _cannon.rotation - 4;
} else if (_cannon.rotation >= 11 && _cannon.rotation < 16)
{
direction = _cannon.rotation - 6;
} else if (_cannon.rotation >= 16 && _cannon.rotation < 21)
{
direction = _cannon.rotation - 8;
} else if (_cannon.rotation >= 21 && _cannon.rotation < 26)
{
direction = _cannon.rotation - 10;
} else if (_cannon.rotation >= 26 && _cannon.rotation < 31)
{
direction = _cannon.rotation - 12;
} else if (_cannon.rotation >= 31 && _cannon.rotation < 36)
{
direction = _cannon.rotation - 14;
} else if (_cannon.rotation >= 36 && _cannon.rotation < 41)
{
direction = _cannon.rotation - 16;
} else if (_cannon.rotation >= 41 && _cannon.rotation < 46)
{
direction = _cannon.rotation - 18;
} else if (_cannon.rotation >= 46 && _cannon.rotation < 55)
{
direction = _cannon.rotation - 20;
} else if (_cannon.rotation <= -1 && _cannon.rotation > -6)
{
direction = _cannon.rotation + 2;
} else if (_cannon.rotation <= -6 && _cannon.rotation > -11)
{
direction = _cannon.rotation + 4;
} else if (_cannon.rotation <= -11 && _cannon.rotation > -16)
{
direction = _cannon.rotation + 6;
} else if (_cannon.rotation <= -16 && _cannon.rotation > -21)
{
direction = _cannon.rotation + 8;
} else if (_cannon.rotation <= -21 && _cannon.rotation > -26)
{
direction = _cannon.rotation + 10;
} else if (_cannon.rotation <= -26 && _cannon.rotation > -31)
{
direction = _cannon.rotation + 12;
} else if (_cannon.rotation <= -31 && _cannon.rotation > -36)
{
direction = _cannon.rotation + 14;
} else if (_cannon.rotation <= -36 && _cannon.rotation > -41)
{
direction = _cannon.rotation + 16;
} else if (_cannon.rotation <= -41 && _cannon.rotation > -46)
{
direction = _cannon.rotation + 18;
} else if (_cannon.rotation <= -46 && _cannon.rotation > -55)
{
direction = _cannon.rotation + 20;
}
I know there has to be an easier way to do this, but I'm still learning. Can someone please help me?

Answer 1

short int val, val2;
val = _cannon.rotation/5;
val2 = _cannon.rotation%5; //remainder of the division
//it will be zero when rotation is a multiple of 5.
if(val2 > 0)
val += 1;
direction = _cannon.rotation - 2*val;
I'm not sure if this is what you want, and I didn't test it. Just made some mental tests to see if it works for the cases you put.
But I hope you can use this as a starting point for making your code smaller.