SKShapeNode not maintaining center position while applying scale

Question

I'm starting to develop a game, and in a moment I need to show a circle which increases its size, I got that, but the problem is that it increases its size and change its position and finally disappear from the screen. I want it to stay on its initial position and increase its size from the initial center.

My code is the following:

CGRect circle = CGRectMake(skRand(0, self.size.width), skRand(0, self.size.height), 20, 20);
SKShapeNode *shapeNode = [[SKShapeNode alloc] init];
shapeNode.position = CGPointMake(skRand(0, self.size.width), skRand(0, self.size.height));
shapeNode.path = [UIBezierPath bezierPathWithOvalInRect:circle].CGPath;
shapeNode.fillColor = [SKColor blueColor];
shapeNode.strokeColor = nil;
[self addChild:shapeNode];
SKAction* zoom = [SKAction scaleTo:15.0 duration:10.0];
[shapeNode runAction:zoom];

Any ideas?

Than you very much!

Answer 1

If you want your circle to increase size from the center, try constructing the circle not by using CGRectMakebut instead use a CGMutablePathRef, make the path and set the circle's path to the one you created. I have something similar in my game and this worked for me:

SKShapeNode *turnSphere = [[SKShapeNode alloc] init];
    CGMutablePathRef path = CGPathCreateMutable();
    CGPathAddArc(path, NULL, 0, 0, 30, 0.0, (2 * M_PI), NO);
    turnSphere.path = path;
    turnSphere.position = CGPointMake(220, 440);
[self addChild:turnSphere];

    [turnSphere runAction:[SKAction scaleBy:3 duration:2]];

The circle should now scale up from the center. Hope this works!