Why does My Rotation only go Anti Clockwise when I want to go Clockwise?

Question

[CATransaction begin];
            [CATransaction setAnimationDuration:5];
            CGAffineTransform currentTransform = squareLayer.affineTransform;
            CGFloat angle = M_PI;

            squareLayer.affineTransform = CGAffineTransformRotate(currentTransform, angle);
            [CATransaction commit];

and

[CATransaction begin];
            [CATransaction setAnimationDuration:5];
            CGAffineTransform currentTransform = squareLayer.affineTransform;
            CGFloat angle = (M_PI * -1);

            squareLayer.affineTransform = CGAffineTransformRotate(currentTransform, angle);
            [CATransaction commit];

I would have thought the -1 would have reversed the direction but apparently not?

Answer 1

EDIT: Instead of -M_PI use -3 * M_PI, for anti-clockwise

and remove '-' sign for opposite direction.

Answer 2

The angle is the same. To go full circle you need 2 * Pi, so half a circle is Pi. If you take -Pi it would end at the same point.

EDIT: If you need to make it turn clockwise you can go slightly off -Pi. Instead of -M_PI use -3.141593 for example.

Answer 3

Just ran into this and while @radicalraid's solution works fine, I prefer adjusting the starting angle before rotation vs rotating to an angle less than the desired end point. Also, you can animate CALayer transforms using animation blocks.

My code:

// iOS will rotate the shortest distance to the end angle,
// using counter-clockwise if equal.
// Force the rotation to open clockwise and close counter-clockwise by bumping
// the initial angle
CGFloat startRadians, endRadians;
if (isOpening) {
    startRadians = 0.01f;
    endRadians = M_PI;

}
else {
    startRadians = M_PI - 0.01f;
    endRadians = 0.0f;
}

self.myImageView.layer.affineTransform = CGAffineTransformMakeRotation(startRadians);

[UIView animateWithDuration:0.3f
                 animations:^{
                     self.myImageView.layer.affineTransform = CGAffineTransformMakeRotation(endRadians);
                 }];