How to join a few rectangle UIBezierPath objects into one? - ios

Question

I simply do the following in code:
let path = UIBezierPath(rect: blurView.bounds)
path.usesEvenOddFillRule = true
path.append(UIBezierPath(rect: CGRect(x: 100, y: 100, width: 100, height: 100)))
path.append(UIBezierPath(rect: CGRect(x: 150, y: 150, width: 100, height: 100)))
//here you can add more paths, but the number is not known
let layer = CAShapeLayer()
layer.path = path.cgPath
layer.fillRule = .evenOdd
blurView.layer.mask = layer
and the effect is following:
Two rectangles overlapping one another. But all I need is to combine area from both rectanges, not to exclude everlapping area. Is it possible?

Answer 1

Using the "even-odd" fill rule is great for "cutting a hole" in a path. However, this code:
// create a big rect
let path = UIBezierPath(rect: blurView.bounds)
// cut a hole in it
path.append(UIBezierPath(rect: CGRect(x: 100, y: 100, width: 100, height: 100)))
// cut a hole overlapping a hole?
path.append(UIBezierPath(rect: CGRect(x: 150, y: 150, width: 100, height: 100)))
will be, as you've seen, problematic.
Depending on what all you are wanting to do, you could use a library such as ClippingBezier which allows you to manipulate paths with boolean actions.
Or, you can use a custom CALayer like this to "invert" multiple paths to use as a "cutout mask":
class BasicCutoutLayer: CALayer {
var rects: [CGRect] = []
func addRect(_ newRect: CGRect) {
rects.append(newRect)
setNeedsDisplay()
}
func reset() {
rects = []
setNeedsDisplay()
}
override func draw(in ctx: CGContext) {
// fill entire layer with solid color
ctx.setFillColor(UIColor.gray.cgColor)
ctx.fill(self.bounds);
rects.forEach { r in
ctx.addPath(UIBezierPath(rect: r).cgPath)
}
// draw clear "cutouts"
ctx.setFillColor(UIColor.clear.cgColor)
ctx.setBlendMode(.sourceIn)
ctx.drawPath(using: .fill)
}
}
To show it in use, we'll use this image:
In a standard UIImageView, overlaid with a blur UIVisualEffectView, and then use the BasicCutoutLayer class with two overlapping rects as the blur view's layer mask:
class BasicCutoutVC: UIViewController {
let myBlurView = UIVisualEffectView()
let myCutoutLayer = BasicCutoutLayer()
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .systemBlue
let imgView = UIImageView()
if let img = UIImage(named: "sampleBG") {
imgView.image = img
}
[imgView, myBlurView].forEach { v in
v.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(v)
}
let g = view.safeAreaLayoutGuide
NSLayoutConstraint.activate([
imgView.topAnchor.constraint(equalTo: g.topAnchor),
imgView.leadingAnchor.constraint(equalTo: g.leadingAnchor),
imgView.trailingAnchor.constraint(equalTo: g.trailingAnchor),
imgView.bottomAnchor.constraint(equalTo: g.bottomAnchor),
myBlurView.topAnchor.constraint(equalTo: g.topAnchor, constant: 0.0),
myBlurView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 0.0),
myBlurView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: 0.0),
myBlurView.bottomAnchor.constraint(equalTo: g.bottomAnchor, constant: 0.0),
])
myBlurView.effect = UIBlurEffect(style: .extraLight)
// set mask for blur view
myBlurView.layer.mask = myCutoutLayer
}
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
// set mask layer frame
myCutoutLayer.frame = myBlurView.bounds
// add two overlapping rects
let v: CGFloat = 160
let c: CGPoint = CGPoint(x: myBlurView.bounds.midX, y: myBlurView.bounds.midY)
var r: CGRect = CGRect(origin: c, size: CGSize(width: v, height: v))
r.origin.x -= v * 0.75
r.origin.y -= v * 0.75
myCutoutLayer.addRect(r)
r.origin.x += v * 0.5
r.origin.y += v * 0.5
myCutoutLayer.addRect(r)
}
}
Before applying the mask, it looks like this:
after applying the mask we get:
As we see, the "overlap" displays as we want.
That was a very simple, basic example. For a more advanced example, take a look at this:
struct MyPath {
var lineWidth: CGFloat = 0
var lineCap: CGLineCap = .butt
var lineJoin: CGLineJoin = .bevel
var isStroked: Bool = true
var isFilled: Bool = true
var pth: UIBezierPath = UIBezierPath()
}
class AdvancedCutoutLayer: CALayer {
var myPaths: [MyPath] = []
func addPath(_ newPath: MyPath) {
myPaths.append(newPath)
setNeedsDisplay()
}
func reset() {
myPaths = []
setNeedsDisplay()
}
override func draw(in ctx: CGContext) {
// fill entire layer with solid color
ctx.setFillColor(UIColor.gray.cgColor)
ctx.fill(self.bounds);
ctx.setBlendMode(.sourceIn)
myPaths.forEach { thisPath in
ctx.setStrokeColor(thisPath.isStroked ? UIColor.clear.cgColor : UIColor.black.cgColor)
ctx.setFillColor(thisPath.isFilled ? UIColor.clear.cgColor : UIColor.black.cgColor)
ctx.setLineWidth(thisPath.isStroked ? thisPath.lineWidth : 0.0)
ctx.setLineCap(thisPath.lineCap)
ctx.setLineJoin(thisPath.lineJoin)
ctx.addPath(thisPath.pth.cgPath)
ctx.drawPath(using: .fillStroke)
}
}
}
along with a subclassed UIVisualEffectView for convenience:
class CutoutBlurView: UIVisualEffectView {
let sl = AdvancedCutoutLayer()
override init(effect: UIVisualEffect?) {
super.init(effect: effect)
commonInit()
}
required init?(coder: NSCoder) {
super.init(coder: coder)
commonInit()
}
func commonInit() {
sl.isOpaque = false
layer.mask = sl
}
override func layoutSubviews() {
super.layoutSubviews()
sl.frame = bounds
sl.setNeedsDisplay()
}
func addPath(_ newPath: MyPath) {
sl.addPath(newPath)
}
func reset() {
sl.reset()
}
}
and an example controller:
class AdvancedCutoutVC: UIViewController {
let myView = CutoutBlurView()
var idx: Int = 0
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .systemBlue
let imgView = UIImageView()
if let img = UIImage(named: "sampleBG") {
imgView.image = img
}
[imgView, myView].forEach { v in
v.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(v)
}
let g = view.safeAreaLayoutGuide
NSLayoutConstraint.activate([
imgView.topAnchor.constraint(equalTo: g.topAnchor),
imgView.leadingAnchor.constraint(equalTo: g.leadingAnchor),
imgView.trailingAnchor.constraint(equalTo: g.trailingAnchor),
imgView.bottomAnchor.constraint(equalTo: g.bottomAnchor),
myView.topAnchor.constraint(equalTo: g.topAnchor),
myView.leadingAnchor.constraint(equalTo: g.leadingAnchor),
myView.trailingAnchor.constraint(equalTo: g.trailingAnchor),
myView.bottomAnchor.constraint(equalTo: g.bottomAnchor),
])
myView.effect = UIBlurEffect(style: .extraLight)
}
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
Timer.scheduledTimer(withTimeInterval: 2.0, repeats: true, block: { _ in
switch self.idx % 4 {
case 1:
self.addSomeOvals()
case 2:
self.addSomeLines()
case 3:
self.addSomeShapes()
default:
self.addSomeRects()
}
self.idx += 1
})
}
func addSomeRects() {
myView.reset()
let w: CGFloat = myView.frame.width / 4.0
let h: CGFloat = myView.frame.height / 4.0
var x: CGFloat = ((myView.frame.width - (w * 5.0 * 0.5)) * 0.5) - (w * 0.25)
var y: CGFloat = ((myView.frame.height - (h * 5.0 * 0.5)) * 0.5) - (h * 0.25)
for _ in 1...5 {
let bz = UIBezierPath(rect: CGRect(x: x, y: y, width: w, height: h))
myView.addPath(MyPath(lineWidth: 0, isStroked: false, isFilled: true, pth: bz))
x += w * 0.5
y += h * 0.5
}
}
func addSomeOvals() {
myView.reset()
let w: CGFloat = myView.frame.width / 4.0
let h: CGFloat = myView.frame.height / 4.0
var x: CGFloat = ((myView.frame.width - (w * 5.0 * 0.5)) * 0.5) - (w * 0.25)
var y: CGFloat = ((myView.frame.height - (h * 5.0 * 0.5)) * 0.5) - (h * 0.25)
for _ in 1...5 {
let bz = UIBezierPath(ovalIn: CGRect(x: x, y: y, width: w, height: h))
myView.addPath(MyPath(lineWidth: 0, isStroked: false, isFilled: true, pth: bz))
x += w * 0.5
y += h * 0.5
}
}
func addSomeLines() {
myView.reset()
let w: CGFloat = myView.frame.width / 2.0
let h: CGFloat = myView.frame.height / 4.0
let x: CGFloat = 80
var y: CGFloat = 80
var lw: CGFloat = 4
for _ in 1...5 {
let bz = UIBezierPath()
bz.move(to: CGPoint(x: x, y: y))
bz.addLine(to: CGPoint(x: x + w, y: y + 20))
myView.addPath(MyPath(lineWidth: lw, lineCap: .round, isStroked: true, isFilled: false, pth: bz))
y += h * 0.5
lw += 10
}
}
func addSomeShapes() {
myView.reset()
var bz: UIBezierPath!
bz = UIBezierPath(rect: CGRect(x: 80, y: 80, width: 80, height: 120))
myView.addPath(MyPath(isStroked: false, isFilled: true, pth: bz))
bz = UIBezierPath(rect: CGRect(x: 120, y: 120, width: 120, height: 60))
myView.addPath(MyPath(isStroked: false, isFilled: true, pth: bz))
bz = UIBezierPath(rect: CGRect(x: 80, y: 220, width: 220, height: 60))
myView.addPath(MyPath(lineWidth: 12, isStroked: true, isFilled: false, pth: bz))
bz = UIBezierPath(ovalIn: CGRect(x: 100, y: 240, width: 220, height: 60))
myView.addPath(MyPath(lineWidth: 12, isStroked: true, isFilled: false, pth: bz))
var r: CGRect = CGRect(x: 40, y: 320, width: myView.frame.width - 80, height: 200)
for _ in 1...4 {
bz = UIBezierPath(rect: r)
myView.addPath(MyPath(lineWidth: 8, isStroked: true, isFilled: false, pth: bz))
r = r.insetBy(dx: 20, dy: 20)
}
}
}
When run, this example will cycle through overlapping rect, overlapping ovals, some varying width lines, and some assorted shapes (just to give an idea):

Answer 2

I would go with ClippingBezier because it is fast, easy to use and neat. It'll be something like this:
let rect1 = CGRect(x: 100, y: 100, width: 200, height: 200)
let rect2 = CGRect(x: 150, y: 200, width: 200, height: 200)
let path0 = UIBezierPath(rect: blurView.bounds)
let path1 = UIBezierPath(rect: rect1)
let path2 = UIBezierPath(rect: rect2)
let unionPathArray = path1.union(with: path2)
let unionPath = UIBezierPath()
if let array = unionPathArray {
array.forEach(unionPath.append)
path0.append(unionPath.reversing())
let layerUnion = CAShapeLayer()
layerUnion.path = path0.cgPath
blurView.layer.mask = layerUnion
}
Output:
EDIT
It appears that this method doesn't work properly when using UIBezierPath(roundedRect:cornerRadius:). To overcome that, here is how we can construct our own func to do that:
extension UIBezierPath {
convenience init(rectangleIn rect: CGRect, cornerRadius: CGFloat) {
self.init()
move(to: CGPoint(x: rect.minX, y: rect.minY + cornerRadius))
addArc(withCenter: CGPoint(x: rect.minX + cornerRadius, y: rect.minY + cornerRadius), radius: cornerRadius, startAngle: .pi, endAngle: 3.0 * .pi / 2.0, clockwise: true)
addLine(to: CGPoint(x: rect.maxX - cornerRadius, y: rect.minY))
addArc(withCenter: CGPoint(x: rect.maxX - cornerRadius, y: rect.minY + cornerRadius), radius: cornerRadius, startAngle: 3.0 * .pi / 2.0, endAngle: 2 * .pi, clockwise: true)
addLine(to: CGPoint(x: rect.maxX, y: rect.maxY - cornerRadius))
addArc(withCenter: CGPoint(x: rect.maxX - cornerRadius, y: rect.maxY - cornerRadius), radius: cornerRadius, startAngle: 0.0, endAngle: .pi / 2.0, clockwise: true)
addLine(to: CGPoint(x: rect.minX + cornerRadius, y: rect.maxY))
addArc(withCenter: CGPoint(x: rect.minX + cornerRadius, y: rect.maxY - cornerRadius), radius: cornerRadius, startAngle: .pi / 2.0, endAngle: .pi, clockwise: true)
//addLine(to: CGPoint(x: rect.minX, y: rect.minY + cornerRadius))
close()
}
}
We can also extend the above-mentioned solution to multiple paths. Here is one way to create the union of multiple paths:
extension UIBezierPath {
class func getUnion(of paths: [UIBezierPath]) -> UIBezierPath {
var result = UIBezierPath()
paths.forEach { subPath in
guard let union = result.union(with: subPath) else { return }
let unionCombined = UIBezierPath()
union.forEach(unionCombined.append)
result = unionCombined
}
return result
}
}
Here is an example:
let rect1 = CGRect(x: 100, y: 100, width: 200, height: 180)
let rect2 = CGRect(x: 150, y: 200, width: 200, height: 200)
let rect3 = CGRect(x: 150, y: 500, width: 100, height: 100)
let rect4 = CGRect(x: 150, y: 800, width: 300, height: 100)
let pathBase = UIBezierPath(rect: blurView.bounds)
let path1 = UIBezierPath(rectangleIn: rect1, cornerRadius: 20.0)
let path2 = UIBezierPath(rect: rect2)
let path3 = UIBezierPath(ovalIn: rect3)
let path4 = UIBezierPath(ovalIn: rect4)
let union = UIBezierPath.getUnion(of: [path1, path2, path3, path4])
pathBase.append(union.reversing())
let layerUnion = CAShapeLayer()
layerUnion.path = pathBase.cgPath
blurView.layer.mask = layerUnion
And the output: