CGAffineTransformMakeRotation goes the other way after 180 degrees (-3.14) - ios

Question

So,
i am trying to do a very simple disc rotation (2d), according to the user touch on it, just like a DJ or something.
It is working, but there is a problem, after certain amount of rotation, it starts going backwards, this amount is after 180 degrees or as i saw in while logging the angle, -3.14 (pi).
I was wondering, how can i achieve a infinite loop, i mean, the user can keep rotating and rotating to any side, just sliding his finger?
Also a second question is, is there any way to speed up the rotation?
Here is my code right now:
#import <UIKit/UIKit.h>
#interface Draggable : UIImageView {
CGPoint firstLoc;
UILabel * fred;
double angle;
}
#property (assign) CGPoint firstLoc;
#property (retain) UILabel * fred;
#end
#implementation Draggable
#synthesize fred, firstLoc;
- (id)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
angle = 0;
if (self) {
// Initialization code
}
return self;
}
-(void)handleObject:(NSSet *)touches
withEvent:(UIEvent *)event
isLast:(BOOL)lst
{
UITouch *touch =[[[event allTouches] allObjects] lastObject];
CGPoint curLoc = [touch locationInView:self];
float fromAngle = atan2( firstLoc.y-self.center.y,
firstLoc.x-self.center.x );
float toAngle = atan2( curLoc.y-(self.center.y+10),
curLoc.x-(self.center.x+10));
float newAngle = angle + (toAngle - fromAngle);
NSLog(#"%f",newAngle);
CGAffineTransform cgaRotate = CGAffineTransformMakeRotation(newAngle);
self.transform = cgaRotate;
if (lst)
angle = newAngle;
}
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch =[[[event allTouches] allObjects] lastObject];
firstLoc = [touch locationInView:self];
};
-(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
[self handleObject:touches withEvent:event isLast:NO];
};
-(void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
[self handleObject:touches withEvent:event isLast:YES];
}
#end
And in the ViewController:
UIImage *tmpImage = [UIImage imageNamed:#"theDisc.png"];
CGRect cellRectangle;
cellRectangle = CGRectMake(-1,self.view.frame.size.height,tmpImage.size.width ,tmpImage.size.height );
dragger = [[Draggable alloc] initWithFrame:cellRectangle];
[dragger setImage:tmpImage];
[dragger setUserInteractionEnabled:YES];
dragger.layer.anchorPoint = CGPointMake(.5,.5);
[self.view addSubview:dragger];
I am open to new/cleaner/more correct ways of doing this too.
Thanks in advance.

Answer 1

Flip the angle if it's below -180 or above 180 degrees. Consider the following touchesMoved implementation:
#implementation RotateView
#define DEGREES_TO_RADIANS(angle) ((angle) / 180.0 * M_PI)
CGFloat angleBetweenLinesInDegrees(CGPoint beginLineA, CGPoint endLineA, CGPoint beginLineB, CGPoint endLineB)
{
CGFloat a = endLineA.x - beginLineA.x;
CGFloat b = endLineA.y - beginLineA.y;
CGFloat c = endLineB.x - beginLineB.x;
CGFloat d = endLineB.y - beginLineB.y;
CGFloat atanA = atan2(a, b);
CGFloat atanB = atan2(c, d);
// convert radians to degrees
return (atanA - atanB) * 180 / M_PI;
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
CGPoint curPoint = [[touches anyObject] locationInView:self];
CGPoint prevPoint = [[touches anyObject] previousLocationInView:self];
// calculate rotation angle between two points
CGFloat angle = angleBetweenLinesInDegrees(self.center, prevPoint, self.center, curPoint);
// Flip
if (angle > 180) {
angle -= 360;
} else if (angle < -180) {
angle += 360;
}
self.layer.transform = CATransform3DRotate(self.layer.transform, DEGREES_TO_RADIANS(angle), .0, .0, 1.0);
}
#end
When dragging around the outer bounds of the view, it will rotate it continuously like a spinning wheel. Hope it helps.

Answer 2

You have some problems here:
1-)
CGPoint curLoc = [touch locationInView:self];
and
firstLoc = [touch locationInView:self];
You are transforming your view, and then asking for the location of a touch in it. You cannot get the correct location of a touch in a rotated view.
Make them something not transformed. (for example self.superview after putting it in a container)
2-)
cellRectangle = CGRectMake(-1,self.view.frame.size.height,tmpImage.size.width ,tmpImage.size.height );
You are placing your Draggable instance out of the screen by passing self.view.frame.size.height as the CGRect's y parameter.