Find the overlapping area of two imageviews overlap, and make this area change colour

问题

I'd like to be able to drag one imageview onto another, such that when they overlap, the overlapping area changes colour. To help visualise the problem, these imageviews are circular: when they overlap, it should form a Venn diagram-style image as shown below.

I know you can detect whether the intersection has occurred by using:

if (self.imageview1.bounds.contains(self.imageview2.bounds)) {
    ...
}

But do not really know how to colour the area in between!

回答1:

so I figured out a way to do this mathematically! Basically you use basic trigonometry to find the angles required for the two "arcs" of the intersection, and make a Bezier Path composed of these two arcs. Then just superpose the bezier path and you're done! Here's my code if anyone is interested :)

Note: this assumes both circles have the same radius, and I have clipped my imageviews such that they are circular!

let circlePath = UIBezierPath()
let left_circle_center = left_image_view.center.x
let right_circle_center = right_image_view.center.x
let radius = left_image_view.frame.width/2
let angle = acos( (left_circle_center - right_circle_center)/radius) 
intersection_Path.addArc(withCenter: right_circle_center, radius: radius, startAngle: CGFloat(Double.pi-angle), endAngle: CGFloat(Double.pi+angle), clockwise: true)
intersection_Path.addArc(withCenter: left_circle_center, radius: radius, startAngle: CGFloat(-angle), endAngle: CGFloat(angle), clockwise: true               
let intersection_area = CAShapeLayer()
intersection_area.path = intersection_Path.cgPath
intersection_area.borderColor = ...
intersection_area.strokeColor = ...
intersection_area.fillColor = ...
self.view.layer.addSublayer(intersection_area)

来源：https://stackoverflow.com/questions/46361119/find-the-overlapping-area-of-two-imageviews-overlap-and-make-this-area-change-c