SpriteKit move rotated physicsBody with applyImpulse

Question

I want to move a physicsBody with the applyImpulse method in a direction based on the physicsBody rotation.

Foe example, the physicsBody is a square in shape, I call a "move" which will apply an impulse to make it move up vertically. I then call a method to rotate the physicsBody 45 degrees right. If I call the "move" method again, the physicsBody will move diagonally right and up.

Can anyone help please?

Answer 1

I suggest that you follow Sprite Kit’s coordinate and rotation conventions. Specifically, your sprite image should be facing right at zero degrees (the default value), and a positive value is a counter-clockwise rotation. That said, here's one way to apply an impulse in the direction a sprite is facing:

// Specify the force to apply to the SKPhysicsBody
CGFloat r = 5;

// Create a vector in the direction the sprite is facing
CGFloat dx = r * cos (sprite.zRotation);
CGFloat dy = r * sin (sprite.zRotation);

// Apply impulse to physics body
[sprite.physicsBody applyImpulse:CGVectorMake(dx,dy)];

Answer 2

UPDATED:

Fixed with the below thanks to @0x141E

-(void)characterJump {

    CGFloat radianFactor = 0.0174532925;
    CGFloat rotationInDegrees = _body.zRotation / radianFactor;
    CGFloat newRotationDegrees = rotationInDegrees + 90;
    CGFloat newRotationRadians = newRotationDegrees * radianFactor;

    CGFloat r = 500;

    CGFloat dx = r * cos(newRotationRadians);
    CGFloat dy = r * sin(newRotationRadians);

    [_body.physicsBody applyImpulse:CGVectorMake(dx, dy)];
}