Track touch points in Multitouch

Question

I am working on a drawing project, I want to support multitouch, I have gone through documentation online, which suggest to track the touch points, I did it , But I am not g

Answer 1

I always try to use gesture-recognizers when possible. Here I use the UIPanGestureRecognizer:

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self.view addGestureRecognizer:[[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(didPan:)]];
}

- (void)didPan:(UIPanGestureRecognizer*)panGesture {
    for (NSUInteger touchIndex = 0; touchIndex < panGesture.numberOfTouches; touchIndex++) {
        // touchIndex is basically the "source" (the finger) from which the point comes from
        CGPoint p = [panGesture locationOfTouch:touchIndex inView:self.view];
        [self drawAtPoint:p withIndex:touchIndex];
    }
}


- (void)drawAtPoint:(CGPoint)point withIndex:(NSUInteger)index{
    UIView *smallPoint = [[UIView alloc] initWithFrame:CGRectMake(point.x, point.y, 3, 3)];
    [smallPoint setBackgroundColor:[self colorForIndex:index]];
    [self.view addSubview:smallPoint];
}

- (UIColor*)colorForIndex:(NSUInteger)index {
    switch (index) {
        case 0: return [UIColor redColor];
        case 1: return [UIColor orangeColor];
        case 2: return [UIColor yellowColor];
        case 3: return [UIColor blueColor];
        case 4: return [UIColor greenColor];
    }
    return [UIColor clearColor];
}

I don't draw a bezier path, but if you drop it in an empty ViewController and run it, you will see that when multi-touching the screen, each finger draws a different colour.

So if you take into consideration the touchIndex, basically you can keep track of different paths for different fingers.

Let's say you use two fingers to draw: you will have panGesture.numberOfTouches == 2, and touchIndex 0 will represent the first finger, and touchIndex 1 will represent the second finger. You can accumulate the points in different arrays and add the points to their corresponding path.