Really need SKSpriteNode children to shoot correctly - ios

Question

So I have a shipNode (which is initially facing right) with two children called _laserCannon1(and 2) that are configured by the method below:
-(void)initializeLaserCannonLocations
{
CGSize size = CGSizeMake(4.0, 4.0);
_laserCannon1 = [SKSpriteNode spriteNodeWithColor:[SKColor yellowColor] size:size];
_laserCannon2 = [SKSpriteNode spriteNodeWithColor:[SKColor yellowColor] size:size];
_laserCannon1.position = CGPointMake(self.size.width/2, self.size.height/2 + 15);
_laserCannon2.position = CGPointMake(self.size.width/2, self.size.height/2 - 15);
[self addChild:_laserCannon1];
[self addChild:_laserCannon2];
}
Then I am later "firing" lasers from them based off of the ship's zRotation as follows
-(void)fireLocalLaser
{
CGVector standardLaserVelocity = CGVectorMake(700*cosf(_myShip.zRotation - _myShip.laserCannon1.zRotation),
700*sinf(_myShip.zRotation - _myShip.laserCannon2.zRotation));
[self spawnLaserFrom:CGPointAdd(_myShip.laserCannon1.position, ship.position); withVelocity:standardLaserVelocity fromShip:_myShip];
[self spawnLaserFrom:CGPointAdd(_myShip.laserCannon2.position, ship.position); withVelocity:standardLaserVelocity fromShip:_myShip];
}
Now everything works fine when the ships is facing directly left or right, but for some odd reason as the ship begins to face more towards the top or bottom the shots are fired increasingly towards the middle of the ship, to the point that once the ship is facing vertically both shots are fired from the middle.position.x of the ship. Does it have to do with something from where I placed my _laserCannons?

Answer 1

I hope my math teacher doesn't see this!
Your problem is with the relative position of your 2 laser cannons as they rotate. I have included a picture so I don't have to go into a long winded description of what is happening.
I have included code for a kinda, sorta, duct tape solution on how you can do this if you really want to. It ain't pretty but it works. The code is good from 0 to 90 degrees so you should be able to work out the rest from there if you have your heart set on having 2 cannons. BUT I would strongly suggest your Mighty Space Empire invest in single cannon ships, as it will make your coding job a whole lot easier!
#implementation MyScene {
SKSpriteNode *ship1;
SKShapeNode *turret1;
SKShapeNode *turret2;
}
-(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];
}
-(void)update:(CFTimeInterval)currentTime {
/* Called before each frame is rendered */
}
// 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 lasers
-(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
{
float turret1offsetX = 0;
float turret1offsetY = 0;
float turret2offsetX = 0;
float turret2offsetY = 0;
if((ship1.zRotation >0) && (ship1.zRotation <=0.785399))
{
turret1offsetX = (14/0.785398) * ship1.zRotation;
turret1offsetY = (23/0.785398) * ship1.zRotation;
turret2offsetX = (-20/0.785398) * ship1.zRotation;
turret2offsetY = (10/0.785398) * ship1.zRotation;
}
if((ship1.zRotation >0.785399) && (ship1.zRotation <=1.570797))
{
turret1offsetX = (14 - (9/0.785398)) * ship1.zRotation;
turret1offsetY = -4 + (27/0.785398) * ship1.zRotation;
turret2offsetX = (3 - (25/0.785398)) * ship1.zRotation;
turret2offsetY = 20 - (10/0.785398) * ship1.zRotation;
}
int x = ship1.position.x + 1000 * cos(ship1.zRotation);
int y = ship1.position.y + 1000 * sin(ship1.zRotation);
turret1 = [SKShapeNode node];
CGMutablePathRef pathToDraw = CGPathCreateMutable();
CGPathMoveToPoint(pathToDraw, NULL, (ship1.position.x+20)+turret1offsetX, (ship1.position.y-25)+turret1offsetY);
CGPathAddLineToPoint(pathToDraw, NULL, x, y);
turret1.path = pathToDraw;
[turret1 setStrokeColor:[UIColor redColor]];
[self addChild:turret1];
turret2 = [SKShapeNode node];
CGMutablePathRef pathToDraw2 = CGPathCreateMutable();
CGPathMoveToPoint(pathToDraw2, NULL, (ship1.position.x+20)+turret2offsetX, (ship1.position.y+25)+turret2offsetY);
CGPathAddLineToPoint(pathToDraw2, NULL, x, y);
turret2.path = pathToDraw2;
[turret2 setStrokeColor:[UIColor redColor]];
[self addChild:turret2];
}
}
-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
[turret1 removeFromParent];
[turret2 removeFromParent];
}
#end

Answer 2

Yes as sangony put it, it really just has to do with your relative positioning of the _laserCannons from your shipNode. I would personally just start with a singular laserCannon for now, and get more comfortable with the math involved until you feel ready to move on to adding more.