How to zoom in/out a drawn circle from the original center of its frame?

Question

I would like to increase or decrease the size of a drawn circle that expands from the center point of its original frame based on a user's pinchGesture as captured by the pinchGestureRecognizer.

So far, the issue I am having is convincing showcasing the expansion of the circle as it comes out from its center. I am able to get the circle to expand, but it always appears as if its expanding from its upper left corner as opposed to the center. I have attached screenshots illustrating the issue:

Here is my code that draws the circle:

    int size = 120;
    int radius = size/2;

    self.tapSelectionView = [[UIView alloc] initWithFrame:CGRectMake(longPressedPoint.x - radius, longPressedPoint.y - radius, size, size)];
    self.tapSelectionView.layer.cornerRadius = radius;
    self.tapSelectionView.layer.borderColor = [UIColor greenColor].CGColor;
    self.tapSelectionView.backgroundColor = [UIColor clearColor];
    self.tapSelectionView.layer.borderWidth = 2;
    [self.view addSubview:self.tapSelectionView];

    CGPoint centerOfOriginalFrame = CGPointMake(self.tapSelectionView.frame.origin.x + radius, self.tapSelectionView.frame.origin.y + radius);
    centerOfDrawnCircle = centerOfOriginalFrame;

And in my pinch gesture method, this is what I am doing:

- (void)pinchGesture: (UIPinchGestureRecognizer *)pinchGestureRecognizer
{
    int size = 120;
    int radius = size/2;

    self.tapSelectionView.layer.cornerRadius = pinchGestureRecognizer.scale * radius;
    self.tapSelectionView.frame = CGRectMake(centerOfDrawnCircle.x - radius, centerOfDrawnCircle.y - radius, size * pinchGestureRecognizer.scale, size * pinchGestureRecognizer.scale);
}

Thanks!

Answer 1

self.tapSelectionView.layer.cornerRadius = pinchGestureRecognizer.scale * radius;
self.tapSelectionView.frame = CGRectMake(centerOfDrawnCircle.x - radius * pinchGestureRecognizer.scale, centerOfDrawnCircle.y - radius * pinchGestureRecognizer.scale, size * pinchGestureRecognizer.scale, size * pinchGestureRecognizer.scale);