Question

How can one image be rotated with axis of rotation as image centre using NSAffineTransform.

Answer 1

You need to translate the origin to the point you want to rotate around, do the rotation and then translate the origin back:

@implementation NSAffineTransform (Rotation)
+ (NSAffineTransform *)transformRotatingAroundPoint:(NSPoint) p byDegrees:(CGFloat) deg
{
    NSAffineTransform * transform = [NSAffineTransform transform];
    [transform translateXBy: p.x yBy: p.y];
    [transform rotateByDegrees:deg];
    [transform translateXBy: -p.x yBy: -p.y];
    return transform;
}
@end

Swift version for CGAffineTransform for use on iOS:

extension CGAffineTransform {
    static func rotationAround(point: CGPoint, byDegrees degrees: CGFloat) -> CGAffineTransform {
        CGAffineTransform()
            .translatedBy(x: point.x, y: point.y)
            .rotated(by: degrees * .pi / 180)
            .translatedBy(x: -point.x, y: -point.y)
    }
}