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I have one UIImageView having an image of an arrow. When user taps on the UIView this arrow should point to the direction of the tap maintaing its position it should just change the transform. I have implemented following code. But it not working as expected. I have added a screenshot. In this screenshot when i touch the point upper left the arrow direction should be as shown.But it is not happening so.

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{

 UITouch *touch=[[event allTouches]anyObject];
 touchedPoint= [touch locationInView:touch.view];
 imageViews.transform = CGAffineTransformMakeRotation(DEGREES_TO_RADIANS(rangle11));
 previousTouchedPoint = touchedPoint ;
}

- (CGFloat) pointPairToBearingDegrees:(CGPoint)startingPoint secondPoint:(CGPoint) endingPoint
{

 CGPoint originPoint = CGPointMake(endingPoint.x - startingPoint.x, endingPoint.y - startingPoint.y); // get origin point to origin by subtracting end from start
   float bearingRadians = atan2f(originPoint.y, originPoint.x); // get bearing in radians
float bearingDegrees = bearingRadians * (180.0 / M_PI); // convert to degrees
bearingDegrees = (bearingDegrees > 0.0 ? bearingDegrees : (360.0 + bearingDegrees)); // correct discontinuity
return bearingDegrees;
}

enter image description here

Prerna chavan
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4 Answers4

5

I assume you wanted an arrow image to point to where ever you touch, I tried and this is what i could come up with. I put an image view with an arrow pointing upwards (haven't tried starting from any other position, log gives correct angles) and on touching on different locations it rotates and points to touched location. Hope it helps ( tried some old math :-) )

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{

    UITouch *touch=[[event allTouches]anyObject];
    touchedPoint= [touch locationInView:touch.view];
    CGFloat angle = [self getAngle:touchedPoint];
    imageView.transform = CGAffineTransformMakeRotation(angle);

}

-(CGFloat) getAngle: (CGPoint) touchedPoints
{
    CGFloat x1 = imageView.center.x;
    CGFloat y1 = imageView.center.y;

    CGFloat x2 = touchedPoints.x;
    CGFloat y2 = touchedPoints.y;

    CGFloat x3 = x1;
    CGFloat y3 = y2;

    CGFloat oppSide = sqrtf(((x2-x3)*(x2-x3)) + ((y2-y3)*(y2-y3)));
    CGFloat adjSide = sqrtf(((x1-x3)*(x1-x3)) + ((y1-y3)*(y1-y3)));

    CGFloat angle = atanf(oppSide/adjSide);
    // Quadrant Identifiaction
    if(x2 < imageView.center.x)
    {
        angle = 0-angle;
    }


    if(y2 > imageView.center.y)
    {
        angle = M_PI/2 + (M_PI/2 -angle);
    }
     NSLog(@"Angle is %2f",angle*180/M_PI);
    return angle;

}

-anoop4real

anoop4real
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  • This answer works completely fine for the arrow pointing upwards. But why is it not working for any other direction? – Prerna chavan Jul 23 '12 at 04:10
  • Hi, this is the idea that i used, I have drawn two lines vertical and horizontal through the image center. Now I coded such that the vertical line drawn through the image center along with the imageview frame will point to the direction that you have tapped. Try putting any image and observe the image frame, you can see it point towards the tapped direction, it is just the position of the image that makes you feel it is not pointing to right dir. Hope you understood, I can post some notes that i used, dont have them right now. – anoop4real Jul 23 '12 at 05:16
1

Given what you told me, I think the problem is that you are not resetting your transform in touchesBegan. Try changing it to something like this and see if it works better:

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{

 UITouch *touch=[[event allTouches]anyObject];
 touchedPoint= [touch locationInView:touch.view];
 imageViews.transform = CGAffineTransformIdentity;
 imageViews.transform = CGAffineTransformMakeRotation(DEGREES_TO_RADIANS(rangle11));
 previousTouchedPoint = touchedPoint ;
}
Paul O.
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1

Do you need the line to "remove the discontinuity"? Seems atan2f() returns values between +π to -π. Won't those work directly with CATransform3DMakeRotation()?

nielsbot
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  • also, `-touchesBegan` will only be called once--you need to also override `-touchesMoved` to update continuously. (And make sure you all `super` from your overrides. – nielsbot Jul 17 '12 at 07:35
1

What you need is that the arrow points to the last tapped point. To simplify and test, I have used a tap gesture (but it's similar to a touchBegan:withEvent:).

In the viewDidLoad method, I register the gesture :

UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapped:)];
[self.view addGestureRecognizer:tapGesture];
[tapGesture release];

The method called on each tap :

- (void)tapped:(UITapGestureRecognizer *)gesture
{
    CGPoint imageCenter = mFlecheImageView.center;
    CGPoint tapPoint = [gesture locationInView:self.view];

    double deltaY = tapPoint.y - imageCenter.y;
    double deltaX = tapPoint.x - imageCenter.x;
    double angleInRadians = atan2(deltaY, deltaX) + M_PI_2;

    mFlecheImageView.transform = CGAffineTransformMakeRotation(angleInRadians);
}

One key is the + M_PI_2 because UIKit coordinates have the origin at the top left corner (while in trigonometric, we use a bottom left corner).

ıɾuǝʞ
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