Shoot from rotating body

Question

I have a rotating enemy body that shoots bullets. It's working pretty good, but it appears to fire in all directions except straight down. It's been a while since I took trig, and I think I'm forgetting something. Do I have to check the rotation of the enemy?

        SKAction *shoot = [SKAction moveTo:CGPointMake(2000*cosf(enemy.zRotation),2000*sinf(enemy.zRotation)) duration:5];
        SKAction *remove = [SKAction removeFromParent];

        [bullet runAction:[SKAction sequence:@[shoot,remove]]];

Ok. I am trying to understand your code's logic. Why don't you use a simple zRotation = XXX on your enemy sprite to rotate your sprite instead of what you have? — sangony, Apr 07 '14 at 21:17
Ah I'm not trying to rotate the enemy sprite or bullet. The enemy is rotating and bullets are firing from it. I want the bullet to fire from the front of the enemy as its rotating. — Negora, Apr 07 '14 at 21:40
Got it. This link might help you in so far that you can substitute the angle value in the equation by your sprites zRotation. Good luck. http://stackoverflow.com/questions/14096138/find-the-point-on-a-circle-with-given-center-point-radius-and-degree — sangony, Apr 07 '14 at 21:54
Or take a look at this tutorial: http://www.raywenderlich.com/57370/trigonometry-game-programming-sprite-kit-version-part-2 — , Apr 08 '14 at 11:23

score 1 · Accepted Answer · answered Apr 10 '14 at 01:55

Here is some code for a ship that can turn 360 degrees and fire from any angle. Touch the left hand side of the screen to slightly rotate the ship and the right side of the screen to shoot.

@implementation MyScene
{
    SKSpriteNode *ship1;
    SKShapeNode *beam1;
}

-(id)initWithSize:(CGSize)size 
{
    if (self = [super initWithSize:size])
    {
        //self.physicsWorld.contactDelegate = self;
        [self createSpaceships];
    }
    return self;
}


-(void)createSpaceships 
{
    ship1 = [SKSpriteNode spriteNodeWithColor:[SKColor blueColor] size:CGSizeMake(50, 50)];
    ship1.position = CGPointMake(300, 150);
    ship1.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:ship1.size];
    ship1.physicsBody.dynamic = NO;
    [self addChild:ship1];

    SKSpriteNode *frontOfShip = [SKSpriteNode spriteNodeWithColor:[SKColor grayColor] size:CGSizeMake(2, 50)];
    frontOfShip.position = CGPointMake(25, 0);
    [ship1 addChild:frontOfShip];
}

// touch the left side of the screen to rotate the ship by +0.0785398 radians
// touch the right hand side of the screen to fire laser

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint touchLocation = [touch locationInNode:self.scene];

    if(touchLocation.x < self.size.width/2) // left side of screen
    {
        SKAction *block0 = [SKAction runBlock:^{
            ship1.zRotation = ship1.zRotation +0.0785398;
        }];
        [self runAction:block0];
    } else // right side of screen
    {
        int x = ship1.position.x + 1000 * cos(ship1.zRotation);
        int y = ship1.position.y + 1000 * sin(ship1.zRotation);

        beam1 = [SKShapeNode node];
        CGMutablePathRef pathToDraw = CGPathCreateMutable();
        CGPathMoveToPoint(pathToDraw, NULL, ship1.position.x, ship1.position.y);
        CGPathAddLineToPoint(pathToDraw, NULL, x, y);
        beam1.path = pathToDraw;
        [beam1 setStrokeColor:[UIColor redColor]];
        [self addChild:beam1];
    }
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    //[beam1 removeFromParent];
}

-(void)update:(CFTimeInterval)currentTime
{
    //
}

@end

Shoot from rotating body

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