How to calculate vector of force to apply to my physics body in Sprite Kit?

1
votes

I'm making a Lular Lander game. I have a Lander object, for simplicity let's imagine it is simple square.

When I tap the screen I apply the force to said square, by default it is CGVectorMake(0,40) This makes the square slowly move up.

Now I want to rotate the sprite based on accelerometer, I do it like so:

// update method

CGFloat updatedAccelX = accelerX;
CGFloat updatedAccelY = -accelerY;
CGFloat angle = vectorAngle(CGPointMake(updatedAccelX, updatedAccelY)) - 1.61;
self.lander.zRotation = angle;

// end of update

static inline CGFloat vectorAngle(CGPoint v){
    return atan2f(v.y, v.x);
}

Now that my rotation has changed, I want to apply the force relative to the new orientation. So for example, my if my Lander rotation is 90 degrees to the right I want to apply (40,0) impulse.

How do I calculate the new vector of force to apply to the physics body?

Adding Box2d as tag since underneath it is Box2d physics.

1
ios7box2dsprite-kit

1 Answers

2
votes

Considering that you have the rotation

float rotation = lander.zRotation;

You can calculate the vector for the lander as follows:

rotation += M_PI_2;

float intensity = 40.0;

CGVector newVec = CGVectorMake(intensity * cosf(rotation), intensity * sinf(rotation));

[lander.physicsBody applyForce:newVec];