Detecting the touch in CAShapeLayer stroke - ios

Question

I have created a simple audio player which plays a single audio. The views shows CAShapeLayer circular progress and also shows current time using CATextLayer. The figure below shows, the view:
Everything works fine until now, I can play, pause and the CAShapeLayer shows the progress. Now, I want to make it so that, when I touch the stroke (track) portion of the CAShapeLayer path, I would want to seek the player to that time. I tried few approaches but I could not detect touches on all parts of the stroke. It seems like the calculations I have done is not quite appropriate. I would be very happy if any body could help me with this.
Here is my complete code,
#interface ViewController ()
#property (nonatomic, weak) CAShapeLayer *progressLayer;
#property (nonatomic, weak) CAShapeLayer *trackLayer;
#property (nonatomic, weak) CATextLayer *textLayer;
#property (nonatomic, strong) AVAudioPlayer *audioPlayer;
#property (nonatomic, weak) NSTimer *audioPlayerTimer;
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
[self prepareLayers];
[self prepareAudioPlayer];
[self prepareGestureRecognizers];
}
- (void)prepareLayers
{
CGFloat lineWidth = 40;
CGRect shapeRect = CGRectMake(0,
0,
CGRectGetWidth(self.view.bounds),
CGRectGetWidth(self.view.bounds));
CGRect actualRect = CGRectInset(shapeRect, lineWidth / 2.0, lineWidth / 2.0);
CGPoint center = CGPointMake(CGRectGetMidX(actualRect), CGRectGetMidY(actualRect));
CGFloat radius = CGRectGetWidth(actualRect) / 2.0;
UIBezierPath *track = [UIBezierPath bezierPathWithArcCenter:center
radius:radius
startAngle:0 endAngle:2 * M_PI
clockwise:true];
UIBezierPath *progressLayerPath = [UIBezierPath bezierPathWithArcCenter:center
radius:radius
startAngle:-M_PI_2
endAngle:2 * M_PI - M_PI_2
clockwise:true];
progressLayerPath.lineWidth = lineWidth;
CAShapeLayer *trackLayer = [CAShapeLayer layer];
trackLayer.contentsScale = [UIScreen mainScreen].scale;
trackLayer.shouldRasterize = YES;
trackLayer.rasterizationScale = [UIScreen mainScreen].scale;
trackLayer.bounds = actualRect;
trackLayer.strokeColor = [UIColor lightGrayColor].CGColor;
trackLayer.fillColor = [UIColor whiteColor].CGColor;
trackLayer.position = self.view.center;
trackLayer.lineWidth = lineWidth;
trackLayer.path = track.CGPath;
self.trackLayer = trackLayer;
CAShapeLayer *progressLayer = [CAShapeLayer layer];
progressLayer.contentsScale = [UIScreen mainScreen].scale;
progressLayer.shouldRasterize = YES;
progressLayer.rasterizationScale = [UIScreen mainScreen].scale;
progressLayer.masksToBounds = NO;
progressLayer.strokeEnd = 0;
progressLayer.bounds = actualRect;
progressLayer.fillColor = nil;
progressLayer.path = progressLayerPath.CGPath;
progressLayer.position = self.view.center;
progressLayer.lineWidth = lineWidth;
progressLayer.lineJoin = kCALineCapRound;
progressLayer.lineCap = kCALineCapRound;
progressLayer.strokeColor = [UIColor redColor].CGColor;
CATextLayer *textLayer = [CATextLayer layer];
textLayer.contentsScale = [UIScreen mainScreen].scale;
textLayer.shouldRasterize = YES;
textLayer.rasterizationScale = [UIScreen mainScreen].scale;
textLayer.font = (__bridge CTFontRef)[UIFont systemFontOfSize:30.0];
textLayer.position = self.view.center;
textLayer.bounds = CGRectMake(0, 0, 300, 100);
[self.view.layer addSublayer:trackLayer];
[self.view.layer addSublayer:progressLayer];
[self.view.layer addSublayer:textLayer];
self.trackLayer = trackLayer;
self.progressLayer = progressLayer;
self.textLayer = textLayer;
[self displayText:#"Play"];
}
- (void)prepareAudioPlayer
{
NSError *error;
self.audioPlayer = [[AVAudioPlayer alloc]
initWithContentsOfURL:[[NSBundle mainBundle] URLForResource:#"Song" withExtension:#"mp3"]
error:&error];
self.audioPlayer.volume = 0.2;
if (!self.audioPlayer) {
NSLog(#"Error occurred, could not create audio player");
return;
}
[self.audioPlayer prepareToPlay];
}
- (void)prepareGestureRecognizers
{
UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self
action:#selector(playerViewTapped:)];
[self.view addGestureRecognizer:tap];
}
- (void)playerViewTapped:(UITapGestureRecognizer *)tap
{
CGPoint tappedPoint = [tap locationInView:self.view];
if ([self.view.layer hitTest:tappedPoint] == self.progressLayer) {
CGPoint locationInProgressLayer = [self.view.layer convertPoint:tappedPoint toLayer:self.progressLayer];
NSLog(#"Progress view tapped %#", NSStringFromCGPoint(locationInProgressLayer));
// this is called sometimes but not always when I tap the stroke
} else if ([self.view.layer hitTest:tappedPoint] == self.textLayer) {
if ([self.audioPlayer isPlaying]) {
[self.audioPlayerTimer invalidate];
[self displayText:#"Play"];
[self.audioPlayer pause];
} else {
[self.audioPlayer play];
self.audioPlayerTimer = [NSTimer scheduledTimerWithTimeInterval:1.0
target:self
selector:#selector(increaseProgress:)
userInfo:nil
repeats:YES];
}
}
}
- (void)increaseProgress:(NSTimer *)timer
{
NSTimeInterval currentTime = self.audioPlayer.currentTime;
NSTimeInterval totalDuration = self.audioPlayer.duration;
float progress = currentTime / totalDuration;
self.progressLayer.strokeEnd = progress;
int minute = ((int)currentTime) / 60;
int second = (int)currentTime % 60;
NSString *progressString = [NSString stringWithFormat:#"%02d : %02d ", minute,second];
[self displayText:progressString];
}
- (void)displayText:(NSString *)text
{
UIColor *redColor = [UIColor redColor];
UIFont *font = [UIFont fontWithName:#"HelveticaNeue" size:70];
NSDictionary *attribtues = #{
NSForegroundColorAttributeName: redColor,
NSFontAttributeName: font,
};
NSAttributedString *progressAttrString = [[NSAttributedString alloc] initWithString:text
attributes:attribtues];
self.textLayer.alignmentMode = kCAAlignmentCenter;
self.textLayer.string = progressAttrString;
}
- (void)viewWillTransitionToSize:(CGSize)size
withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator
{
[super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];
void(^animationBlock)(id<UIViewControllerTransitionCoordinatorContext>) =
^(id<UIViewControllerTransitionCoordinatorContext> context) {
CGRect rect = (CGRect){.origin = CGPointZero, .size = size};
CGPoint center = CGPointMake(CGRectGetMidX(rect), CGRectGetMidY(rect));
self.progressLayer.position = center;
self.textLayer.position = center;
self.trackLayer.position = center;
};
[coordinator animateAlongsideTransitionInView:self.view
animation:animationBlock completion:nil];
}
#end

Answer 1

As far as I know the CALAyer hitTest method does a very primitive bounds check. If the point is inside the layer's bounds, it returns YES, otherwise it returns NO.
CAShapeLayer doesn't make any attempt to tell if the point intersects the shape layer's path.
UIBezierPath does have a hitTest method, but I'm pretty sure that detects touches in the interior of a closed path, and would not work with a thick line arc line the one you're using.
If you want to hit test using paths I think you're going to have to roll your own hitTest logic that builds a UIBezierPath that is a closed path defining the shape you are testing for (your thick arc line). Doing that for an animation that's in-flight might be too slow.
Another problem you'll face: You're interrogating a layer that has an in-flight animation. Even when you're simply animating the center property of a layer that doesn't work. Instead you have to interrogate the layer's presentationLayer, which is a layer that approximates the settings of an in-flight animation.
I think your best solution will be to take the starting and ending position of your arc, convert the start-to end value to starting and ending angles, use trig to convert your touch position to an angle and radius, and see if the touch position is in the range of the start-to-end touch and within the inner and outer radius of the indicator line. That would just require some basic trig.
Edit:
Hint: The trig function you want to use to convert x and y position to an angle is arc tangent. arc tangent takes an X and a Y value and gives back an angle. However, to use the arc tangent properly you need to implement a bunch of logic to figure out what quadrant of the circle your point is in.In C, the math library function you want is atan2(). The atan2() function takes care of everything for you. You'll convert your point so 0,0 is in the center, and atan2() will give you the angle along the circle. To calculate the distance from the center of the circle you use the distance formula, a² + b² = c².