UIImage which follow touches - ios

Question

I'm trying to draw a ruller which follow the touches on the screen. On the first touch, I set the first point and on all the other, the ruller follow the finger on ther screen resizing and rotating around the first point depending on where the finger is.
I tried to do this :
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [touches anyObject];
CGPoint p = [touch locationInView:self.view];
self.regleFirstPoint = p;
UIImageView* img = [[UIImageView alloc] initWithImage:self.regleImg];
img.frame = CGRectMake(self.regleFirstPoint.x, self.regleFirstPoint.y, 0, self.regleImg.size.height);
[self.view addSubview:img];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [touches anyObject];
CGPoint p = [touch locationInView:self.view];
// Width
float deltaY = p.y - self.regleFirstPoint.y;
float deltaX = p.x - self.regleFirstPoint.x;
float width = sqrt((deltaX * deltaX) + (deltaY * deltaY));
// Angle
float angleInRadians = atanf(deltaY / deltaX);
float angleInDegrees = angleInRadians * 180 / M_PI; // JUST FOR INFO
NSLog(#"angle : %f / %f", angleInRadians, angleInDegrees);
// Resizing image
UIImageView* img = [self.regles lastObject];
img.frame = CGRectMake(self.regleFirstPoint.x, self.regleFirstPoint.y, width, self.regleImg.size.height/2);
img.center = self.regleFirstPoint;
CGAffineTransform transform = CGAffineTransformIdentity;
img.transform = CGAffineTransformRotate(transform, angleInRadians);
}
The ruller doesn't follow the finger correctly, I think I missed something. What's wrong with my code ?
EDIT : I also tried this after some researches :
// Resizing images
img.frame = CGRectMake(self.regleFirstPoint.x, self.regleFirstPoint.y, largeur, self.regleImg.size.height/2);
[img.layer setAnchorPoint:CGPointMake(self.regleFirstPoint.x / img.bounds.size.width, self.regleFirstPoint.y / img.bounds.size.height)];
img.transform = CGAffineTransformRotate(img.transform, angleInRadians);

Answer 1

This is just a question of order:
Set transform of your view to identity
Change the frame of your view
Finally, apply your transform
Here is an updated piece of code, just used an UIView instead of your image:
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
// Hold first touch
self.regleFirstPoint = [touch locationInView:self.view];
// Reset view / image
_rulerView.transform = CGAffineTransformIdentity;
_rulerView.frame = CGRectMake(self.regleFirstPoint.x, self.regleFirstPoint.y, 0, CGRectGetHeight(_rulerView.frame));
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
CGPoint p = [touch locationInView:self.view];
// Compute width
float deltaX = p.x - self.regleFirstPoint.x;
float deltaY = p.y - self.regleFirstPoint.y;
float width = sqrt((deltaX * deltaX) + (deltaY * deltaY));
// Compute angle
float angleInRadians = atan2(deltaY, deltaX);
NSLog(#"angle (rad) : %f", angleInRadians);
NSLog(#"angle (deg) : %f", angleInRadians * 180 / M_PI);
// First reset the transformation to identity
_rulerView.transform = CGAffineTransformIdentity;
// Set anchor point
_rulerView.layer.anchorPoint = CGPointMake(0.0f, 0.5f);
// Resizing view / image
_rulerView.frame = CGRectMake(self.regleFirstPoint.x, self.regleFirstPoint.y, width, CGRectGetHeight(_rulerView.frame));
// Reset the layer position to the first point
_rulerView.layer.position = self.regleFirstPoint;
// Apply rotation transformation
_rulerView.transform = CGAffineTransformMakeRotation(angleInRadians);
}
Hope that helps.
Cyril