core graphics绘图时如何跳过一个区域（cutout）
How to skip an area (cutout) when drawing with core graphics
我想绘制一些项目，但为圆形区域留下真正的 alpha 透明度切口。我想达到的目标：
黄色是显示渗色的示例背景。
切口宽度实际上比弧线更宽，所以它们没有完全相交。我需要真正的剪切图，因为我要保存为具有透明度的图像。
我想也许我可以使用 setBlendMode()，但我相信只有当我希望我的切口与弧的宽度完全相同时，它才会起作用。但是我试图解决它的要点是：
Swift 工作簿如下。非常感谢有关实现此目的的任何提示。
import Foundation
import UIKit
var dimen: CGFloat = 200.0;
var strokeWidth: CGFloat = 20.0;
var cutoutWidth: CGFloat = 30.0;
class DonutView : UIView
{
override func draw(_ rect: CGRect)
{
// cutout
let cutoutColor = UIColor(red: 1, green: 0, blue: 0, alpha: 1)
cutoutColor.setFill()
let cutoutPath = UIBezierPath(ovalIn: CGRect(x: dimen-cutoutWidth, y: dimen/2-cutoutWidth/2, width: cutoutWidth, height: cutoutWidth))
cutoutPath.fill()
// let context = UIGraphicsGetCurrentContext()!
// context.setBlendMode(.sourceOut)
let ringOffset = cutoutWidth/2;
let circleWidth = dimen - ringOffset*2;
// ring
let ringPath = UIBezierPath(ovalIn: CGRect(x: ringOffset, y: ringOffset, width: circleWidth, height: circleWidth))
let ringColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.3)
ringColor.setStroke()
ringPath.lineWidth = strokeWidth
ringPath.stroke()
// arc
let arcRect = CGRect(x: ringOffset, y: ringOffset, width: circleWidth, height: circleWidth)
let arcPath = UIBezierPath()
arcPath.addArc(withCenter: CGPoint(x: arcRect.midX, y: arcRect.midY), radius: arcRect.width / 2, startAngle: -90 * CGFloat.pi/180, endAngle: 37 * CGFloat.pi/180, clockwise: true)
let arcColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.6)
arcColor.setStroke()
arcPath.lineWidth = strokeWidth
arcPath.stroke()
}
}
var view = DonutView(frame: CGRect.init(x: 0, y: 0, width: dimen, height: dimen))
view.backgroundColor = UIColor.yellow
// View these elements
view
（编辑：我应该在一开始就说明这一点：这是最终为 WatchKit 创建一个 UIImage）
在
的帮助下
import Foundation
import UIKit
import PlaygroundSupport
var dimen: CGFloat = 200.0;
var strokeWidth: CGFloat = 20.0;
var cutoutWidth: CGFloat = 30.0;
class DonutView : UIImageView
{
override init(frame: CGRect) {
super.init(frame: frame)
UIGraphicsBeginImageContextWithOptions(CGSize(width: dimen, height: dimen), false, 1)
let context = UIGraphicsGetCurrentContext()!
let ringOffset = cutoutWidth/2;
let circleWidth = dimen - ringOffset*2;
// ring
let ringPath = UIBezierPath(ovalIn: CGRect(x: ringOffset, y: ringOffset, width: circleWidth, height: circleWidth))
let ringColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.3)
ringColor.setStroke()
ringPath.lineWidth = strokeWidth
ringPath.stroke()
// arc
let arcRect = CGRect(x: ringOffset, y: ringOffset, width: circleWidth, height: circleWidth)
let arcPath = UIBezierPath()
arcPath.addArc(withCenter: CGPoint(x: arcRect.midX, y: arcRect.midY), radius: arcRect.width / 2, startAngle: -90 * CGFloat.pi/180, endAngle: 37 * CGFloat.pi/180, clockwise: true)
let arcColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.6)
arcColor.setStroke()
arcPath.lineWidth = strokeWidth
arcPath.stroke()
// Cutout circle
context.setFillColor(UIColor.clear.cgColor)
context.setBlendMode(.clear)
context.addEllipse(in: CGRect(x: dimen-cutoutWidth, y: dimen/2-cutoutWidth/2, width: cutoutWidth, height: cutoutWidth))
context.drawPath(using: .fill)
context.setBlendMode(.normal)
image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
}
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
var view = DonutView(frame: CGRect.init(x: 0, y: 0, width: dimen, height: dimen))
view.backgroundColor = UIColor.yellow
// View these elements
view
您可以使用另一个 CAShapeLayer 作为掩码来完成此操作。
alpha = 1.0 的遮罩层部分将完全透明。
所以...
如果我们将 Arc Layer 设为 Ring Layer 的子层，然后我们可以将 Cutout Layer 用作蒙版，结果：
这是 Playground 页面的来源：
class MyDonutView : UIView
{
let ringLayer = CAShapeLayer()
let arcLayer = CAShapeLayer()
let cutoutLayer = CAShapeLayer()
var strokeWidth: CGFloat = 20.0;
var cutoutWidth: CGFloat = 30.0;
override init(frame: CGRect) {
super.init(frame: frame)
commonInit()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
commonInit()
}
func commonInit() -> Void {
// add arcLayer as a sublayer of ringLayer
ringLayer.addSublayer(arcLayer)
// add ringLayer as a sublayer of self.layer
layer.addSublayer(ringLayer)
// ring layer stroke is black at 0.3 alpha, fill is clear
ringLayer.strokeColor = UIColor(red: 0.0, green: 0.0, blue: 0.0, alpha: 0.3).cgColor
ringLayer.fillColor = UIColor.clear.cgColor
ringLayer.lineWidth = strokeWidth
// arc layer stroke is black at 0.6 alpha, fill is clear
arcLayer.strokeColor = UIColor(red: 0.0, green: 0.0, blue: 0.0, alpha: 0.6).cgColor
arcLayer.lineWidth = strokeWidth
arcLayer.fillColor = UIColor.clear.cgColor
// cutout layer stroke is black (although we're using Zero line width
// fill is black
cutoutLayer.strokeColor = UIColor.red.cgColor
cutoutLayer.lineWidth = 0
cutoutLayer.fillColor = UIColor.red.cgColor
}
override func layoutSubviews() {
super.layoutSubviews()
// define the "padding" around the ring
let ringOffset = cutoutWidth / 2.0
// define the diameter of the ring
let circleWidth = bounds.size.width - cutoutWidth;
// ring path
let ringPath = UIBezierPath(ovalIn: CGRect(x: ringOffset, y: ringOffset, width: circleWidth, height: circleWidth))
// arc path
let arcRect = CGRect(x: ringOffset, y: ringOffset, width: circleWidth, height: circleWidth)
let arcPath = UIBezierPath()
arcPath.addArc(withCenter: CGPoint(x: arcRect.midX, y: arcRect.midY), radius: arcRect.width / 2, startAngle: -90 * CGFloat.pi/180, endAngle: 37 * CGFloat.pi/180, clockwise: true)
// set ring layer path
ringLayer.path = ringPath.cgPath
// set arc layer path
arcLayer.path = arcPath.cgPath
// create a rect path the full size of bounds of self
let fullPath = UIBezierPath(rect: bounds)
// create a cutout path (the small circle to cut-out of the ring/arc)
let cutoutPath = UIBezierPath(ovalIn: CGRect(x: bounds.size.width-cutoutWidth, y: bounds.size.width/2-cutoutWidth/2, width: cutoutWidth, height: cutoutWidth))
// append the cutout path to the full rect path
fullPath.append(cutoutPath)
// even-odd winding rule
cutoutLayer.fillRule = CAShapeLayerFillRule.evenOdd
// set cutout layer path
cutoutLayer.path = fullPath.cgPath
// use cutout layer to mask ring layer
ringLayer.mask = cutoutLayer
}
}
class TestViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .white
// instantiate a MyDonutView
let myDonutView = MyDonutView()
// we can set the stroke and cutout widths here
myDonutView.strokeWidth = 20.0
myDonutView.cutoutWidth = 30.0
// we're using auto-layout
myDonutView.translatesAutoresizingMaskIntoConstraints = false
// background color yellow to see the frame
//myDonutView.backgroundColor = .yellow
// otherwise, it should be clear
myDonutView.backgroundColor = .clear
// add as subview
view.addSubview(myDonutView)
// constrain centerX and centerY
// width = 200, height = width
NSLayoutConstraint.activate([
myDonutView.widthAnchor.constraint(equalToConstant: 200.0),
myDonutView.heightAnchor.constraint(equalTo: myDonutView.widthAnchor),
myDonutView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
myDonutView.centerYAnchor.constraint(equalTo: view.centerYAnchor),
])
}
}
let vc = TestViewController()
PlaygroundPage.current.liveView = vc
我想绘制一些项目，但为圆形区域留下真正的 alpha 透明度切口。我想达到的目标：
黄色是显示渗色的示例背景。
切口宽度实际上比弧线更宽，所以它们没有完全相交。我需要真正的剪切图，因为我要保存为具有透明度的图像。
我想也许我可以使用 setBlendMode()，但我相信只有当我希望我的切口与弧的宽度完全相同时，它才会起作用。但是我试图解决它的要点是：
Swift 工作簿如下。非常感谢有关实现此目的的任何提示。
import Foundation
import UIKit
var dimen: CGFloat = 200.0;
var strokeWidth: CGFloat = 20.0;
var cutoutWidth: CGFloat = 30.0;
class DonutView : UIView
{
override func draw(_ rect: CGRect)
{
// cutout
let cutoutColor = UIColor(red: 1, green: 0, blue: 0, alpha: 1)
cutoutColor.setFill()
let cutoutPath = UIBezierPath(ovalIn: CGRect(x: dimen-cutoutWidth, y: dimen/2-cutoutWidth/2, width: cutoutWidth, height: cutoutWidth))
cutoutPath.fill()
// let context = UIGraphicsGetCurrentContext()!
// context.setBlendMode(.sourceOut)
let ringOffset = cutoutWidth/2;
let circleWidth = dimen - ringOffset*2;
// ring
let ringPath = UIBezierPath(ovalIn: CGRect(x: ringOffset, y: ringOffset, width: circleWidth, height: circleWidth))
let ringColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.3)
ringColor.setStroke()
ringPath.lineWidth = strokeWidth
ringPath.stroke()
// arc
let arcRect = CGRect(x: ringOffset, y: ringOffset, width: circleWidth, height: circleWidth)
let arcPath = UIBezierPath()
arcPath.addArc(withCenter: CGPoint(x: arcRect.midX, y: arcRect.midY), radius: arcRect.width / 2, startAngle: -90 * CGFloat.pi/180, endAngle: 37 * CGFloat.pi/180, clockwise: true)
let arcColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.6)
arcColor.setStroke()
arcPath.lineWidth = strokeWidth
arcPath.stroke()
}
}
var view = DonutView(frame: CGRect.init(x: 0, y: 0, width: dimen, height: dimen))
view.backgroundColor = UIColor.yellow
// View these elements
view
（编辑：我应该在一开始就说明这一点：这是最终为 WatchKit 创建一个 UIImage）
在
import Foundation
import UIKit
import PlaygroundSupport
var dimen: CGFloat = 200.0;
var strokeWidth: CGFloat = 20.0;
var cutoutWidth: CGFloat = 30.0;
class DonutView : UIImageView
{
override init(frame: CGRect) {
super.init(frame: frame)
UIGraphicsBeginImageContextWithOptions(CGSize(width: dimen, height: dimen), false, 1)
let context = UIGraphicsGetCurrentContext()!
let ringOffset = cutoutWidth/2;
let circleWidth = dimen - ringOffset*2;
// ring
let ringPath = UIBezierPath(ovalIn: CGRect(x: ringOffset, y: ringOffset, width: circleWidth, height: circleWidth))
let ringColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.3)
ringColor.setStroke()
ringPath.lineWidth = strokeWidth
ringPath.stroke()
// arc
let arcRect = CGRect(x: ringOffset, y: ringOffset, width: circleWidth, height: circleWidth)
let arcPath = UIBezierPath()
arcPath.addArc(withCenter: CGPoint(x: arcRect.midX, y: arcRect.midY), radius: arcRect.width / 2, startAngle: -90 * CGFloat.pi/180, endAngle: 37 * CGFloat.pi/180, clockwise: true)
let arcColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.6)
arcColor.setStroke()
arcPath.lineWidth = strokeWidth
arcPath.stroke()
// Cutout circle
context.setFillColor(UIColor.clear.cgColor)
context.setBlendMode(.clear)
context.addEllipse(in: CGRect(x: dimen-cutoutWidth, y: dimen/2-cutoutWidth/2, width: cutoutWidth, height: cutoutWidth))
context.drawPath(using: .fill)
context.setBlendMode(.normal)
image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
}
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
var view = DonutView(frame: CGRect.init(x: 0, y: 0, width: dimen, height: dimen))
view.backgroundColor = UIColor.yellow
// View these elements
view
您可以使用另一个 CAShapeLayer 作为掩码来完成此操作。
alpha = 1.0 的遮罩层部分将完全透明。
所以...
如果我们将 Arc Layer 设为 Ring Layer 的子层，然后我们可以将 Cutout Layer 用作蒙版，结果：
这是 Playground 页面的来源：
class MyDonutView : UIView
{
let ringLayer = CAShapeLayer()
let arcLayer = CAShapeLayer()
let cutoutLayer = CAShapeLayer()
var strokeWidth: CGFloat = 20.0;
var cutoutWidth: CGFloat = 30.0;
override init(frame: CGRect) {
super.init(frame: frame)
commonInit()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
commonInit()
}
func commonInit() -> Void {
// add arcLayer as a sublayer of ringLayer
ringLayer.addSublayer(arcLayer)
// add ringLayer as a sublayer of self.layer
layer.addSublayer(ringLayer)
// ring layer stroke is black at 0.3 alpha, fill is clear
ringLayer.strokeColor = UIColor(red: 0.0, green: 0.0, blue: 0.0, alpha: 0.3).cgColor
ringLayer.fillColor = UIColor.clear.cgColor
ringLayer.lineWidth = strokeWidth
// arc layer stroke is black at 0.6 alpha, fill is clear
arcLayer.strokeColor = UIColor(red: 0.0, green: 0.0, blue: 0.0, alpha: 0.6).cgColor
arcLayer.lineWidth = strokeWidth
arcLayer.fillColor = UIColor.clear.cgColor
// cutout layer stroke is black (although we're using Zero line width
// fill is black
cutoutLayer.strokeColor = UIColor.red.cgColor
cutoutLayer.lineWidth = 0
cutoutLayer.fillColor = UIColor.red.cgColor
}
override func layoutSubviews() {
super.layoutSubviews()
// define the "padding" around the ring
let ringOffset = cutoutWidth / 2.0
// define the diameter of the ring
let circleWidth = bounds.size.width - cutoutWidth;
// ring path
let ringPath = UIBezierPath(ovalIn: CGRect(x: ringOffset, y: ringOffset, width: circleWidth, height: circleWidth))
// arc path
let arcRect = CGRect(x: ringOffset, y: ringOffset, width: circleWidth, height: circleWidth)
let arcPath = UIBezierPath()
arcPath.addArc(withCenter: CGPoint(x: arcRect.midX, y: arcRect.midY), radius: arcRect.width / 2, startAngle: -90 * CGFloat.pi/180, endAngle: 37 * CGFloat.pi/180, clockwise: true)
// set ring layer path
ringLayer.path = ringPath.cgPath
// set arc layer path
arcLayer.path = arcPath.cgPath
// create a rect path the full size of bounds of self
let fullPath = UIBezierPath(rect: bounds)
// create a cutout path (the small circle to cut-out of the ring/arc)
let cutoutPath = UIBezierPath(ovalIn: CGRect(x: bounds.size.width-cutoutWidth, y: bounds.size.width/2-cutoutWidth/2, width: cutoutWidth, height: cutoutWidth))
// append the cutout path to the full rect path
fullPath.append(cutoutPath)
// even-odd winding rule
cutoutLayer.fillRule = CAShapeLayerFillRule.evenOdd
// set cutout layer path
cutoutLayer.path = fullPath.cgPath
// use cutout layer to mask ring layer
ringLayer.mask = cutoutLayer
}
}
class TestViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .white
// instantiate a MyDonutView
let myDonutView = MyDonutView()
// we can set the stroke and cutout widths here
myDonutView.strokeWidth = 20.0
myDonutView.cutoutWidth = 30.0
// we're using auto-layout
myDonutView.translatesAutoresizingMaskIntoConstraints = false
// background color yellow to see the frame
//myDonutView.backgroundColor = .yellow
// otherwise, it should be clear
myDonutView.backgroundColor = .clear
// add as subview
view.addSubview(myDonutView)
// constrain centerX and centerY
// width = 200, height = width
NSLayoutConstraint.activate([
myDonutView.widthAnchor.constraint(equalToConstant: 200.0),
myDonutView.heightAnchor.constraint(equalTo: myDonutView.widthAnchor),
myDonutView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
myDonutView.centerYAnchor.constraint(equalTo: view.centerYAnchor),
])
}
}
let vc = TestViewController()
PlaygroundPage.current.liveView = vc