ios - 径向 CAGradientLayer 在运行时无法正确渲染
问题描述
我正在尝试快速创建一个径向 CAGradientLayer。普通的 CAGradientLayers (默认类型axial
)没有问题。它们在模拟器中的快照和运行时渲染良好。
当我拍摄我创建的 UIView(仅用于 CAGradientLayer)的快照时,它显示了一个漂亮的径向 CAGradientLayer。但是,当我使用这个视图并在模拟器中运行时查看它时,它看起来很糟糕。我不知道我做错了什么。
这是 CAGradientLayer 的代码:
import Foundation
class ChannelGradientView: UIView {
// MARK: - Init
override init(frame: CGRect) {
super.init(frame: frame)
setup()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setup()
}
// MARK: - Setup
private func setup() {
backgroundColor = .clear
setupGradient()
}
private func setupGradient() {
let gradient = layer as? CAGradientLayer
gradient?.type = .radial
gradient?.colors = [
UIColor.black.withAlphaComponent(0.8),
UIColor.black.withAlphaComponent(0)
].map { $0.cgColor }
let blackPoint = CGPoint(x: 1, y: 0)
let clearPoint = CGPoint(x: 1, y: 1)
// startpoint is center (for example black here)
gradient?.startPoint = blackPoint
gradient?.endPoint = clearPoint
}
// MARK: - Layer
override public class var layerClass: Swift.AnyClass {
return CAGradientLayer.self
}
}
这是我进行快照单元测试时的样子(使用 Nimble Snapshot 库):
这就是它在模拟器上运行时的样子:
任何人都知道我做错了什么?
编辑:在实际设备上运行,它甚至不显示任何渐变层,甚至不显示蹩脚的。这是一个透明的盒子。
解决方案
不确定您在 Simulator vs Device 上看到的内容之间还会发生什么,但是...
如果我按原样使用您的代码,我会得到这个(红色边框显示框架):
如果我改变你的clearPoint
:
//let clearPoint = CGPoint(x: 1, y: 1)
let clearPoint = CGPoint(x: 0, y: 1) // bottom-left-corner
我明白了:
模拟器和设备上的外观相同
编辑
一些额外的澄清......
径向渐变与(线性)渐变不使用.startPoint
相同的.endPoint
方式。.axial
使用.radial
,绘制一个渐变*椭圆,使用.startPoint
为中心,startPoint.x
与endPoint.x
乘以 2 之差为宽度,startPoint.y
与endPoint.y
乘以 2 之差为高度。
因此,要获得所需的从右上角到左下角的径向渐变,您需要设置.startPoint
to1,0
和.endPoint
to 值,从而生成大小为椭圆形的渐变2 x 2
:
startPoint = 1,0
endPoint = 0,1
width: abs(1 - 0) * 2 = 2
height: abs(0 - 1) * 2 = 2
请注意,您可以通过以下方式获得相同的结果:
startPoint = 1,0
endPoint = 2,-1
width: abs(1 - 2) * 2 = 2
height: abs(0 - (-1)) * 2 = 2
.radial
渐变不喜欢将其宽度或高度设置为零,这就是我们得到的:
startPoint = 1,0
endPoint = 1,1
width: abs(1 - 1) * 2 = 0 // problem!!!!
height: abs(0 - 1) * 2 = 2
正如我们所见,结果是奇怪的线条图案。
这里有一些实际的例子来演示。
轴向/线性右上角到左下角:
径向居中且宽度 = 视图宽度 / 高度 = 视图高度:
径向居中且宽度 = 视图宽度的二分之一 / 高度 = 视图高度:
径向居中和宽度 = 一半视图宽度 / 高度 = 视图高度...结果完全相同,但请注意该.endPoint.x
值0.75
不是0.25
:
现在我们改变.startPoint.x = 0.75
,但我们离开.endPoint.x = 0.25
,所以椭圆的中心移动到视图宽度的 3/4,但椭圆的宽度变得等于视图的宽度...... abs(0.75 - 0.25) * 2 == 1.0
:
更改.endPoint.x = 0.5
并且宽度返回到视图宽度的 1/2... abs(0.75 - 0.5) * 2 = 0.5
:
最后是从右上角到左下角的径向渐变:
这是我用来生成这些图像的代码。它有一个“梯度定义”的数据块......您可以添加/更改这些定义以试验差异。
//
// GradTestViewController.swift
//
// Created by Don Mag on 9/12/19.
//
import UIKit
class TestGradientView: UIView {
// MARK: - Init
override init(frame: CGRect) {
super.init(frame: frame)
setup()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setup()
}
// MARK: - Setup
private func setup() {
// just set the background to clear and the
// gradient colors to blue -> green
backgroundColor = .clear
if let gradient = layer as? CAGradientLayer {
gradient.colors = [
UIColor.blue,
UIColor.green,
].map { $0.cgColor }
}
}
// MARK: - Layer
override public class var layerClass: Swift.AnyClass {
return CAGradientLayer.self
}
}
struct GradDef {
var gradType: CAGradientLayerType = .axial
var startPoint: CGPoint = CGPoint(x: 1.0, y: 0.0)
var endPoint: CGPoint = CGPoint(x: 0.0, y: 1.0)
}
class GradTestViewController: UIViewController {
var theButton: UIButton = {
let v = UIButton()
v.setTitle("Tap", for: .normal)
v.setTitleColor(.white, for: .normal)
v.setTitleColor(.lightGray, for: .highlighted)
v.backgroundColor = .red
return v
}()
var counterLabel: UILabel = {
let v = UILabel()
return v
}()
var descLabel: UILabel = {
let v = UILabel()
v.numberOfLines = 0
return v
}()
var gradContainerView: UIView = {
let v = UIView()
return v
}()
var gradView: TestGradientView = {
let v = TestGradientView()
return v
}()
var tlLabel: UILabel = {
let v = UILabel()
v.text = "0,0"
return v
}()
var trLabel: UILabel = {
let v = UILabel()
v.text = "1,0"
return v
}()
var blLabel: UILabel = {
let v = UILabel()
v.text = "0,1"
return v
}()
var brLabel: UILabel = {
let v = UILabel()
v.text = "1,1"
return v
}()
var theStackView: UIStackView = {
let v = UIStackView()
v.axis = .vertical
v.alignment = .center
v.distribution = .fill
v.spacing = 20.0
return v
}()
var gradDefs: [GradDef] = [
GradDef(gradType: .axial, startPoint: CGPoint(x: 1.0, y: 0.0), endPoint: CGPoint(x: 0.0, y: 1.0)),
GradDef(gradType: .radial, startPoint: CGPoint(x: 0.5, y: 0.5), endPoint: CGPoint(x: 0.0, y: 0.0)),
GradDef(gradType: .radial, startPoint: CGPoint(x: 0.5, y: 0.5), endPoint: CGPoint(x: 0.25, y: 0.0)),
GradDef(gradType: .radial, startPoint: CGPoint(x: 0.5, y: 0.5), endPoint: CGPoint(x: 0.75, y: 0.0)),
GradDef(gradType: .radial, startPoint: CGPoint(x: 0.75, y: 0.5), endPoint: CGPoint(x: 0.25, y: 0.0)),
GradDef(gradType: .radial, startPoint: CGPoint(x: 0.75, y: 0.5), endPoint: CGPoint(x: 1.0, y: 0.0)),
GradDef(gradType: .radial, startPoint: CGPoint(x: 1.0, y: 0.0), endPoint: CGPoint(x: 0.0, y: 1.0)),
]
var idx: Int = 0
override func viewDidLoad() {
super.viewDidLoad()
[theButton, counterLabel, gradContainerView, gradView, tlLabel, trLabel, blLabel, brLabel, descLabel, theStackView].forEach {
$0.translatesAutoresizingMaskIntoConstraints = false
}
[theButton, counterLabel, gradContainerView, descLabel].forEach {
theStackView.addArrangedSubview($0)
}
[gradView, tlLabel, trLabel, blLabel, brLabel].forEach {
gradContainerView.addSubview($0)
}
[counterLabel, tlLabel, trLabel, blLabel, brLabel, descLabel].forEach {
$0.font = UIFont.monospacedDigitSystemFont(ofSize: 14.0, weight: .regular)
}
NSLayoutConstraint.activate([
gradView.widthAnchor.constraint(equalToConstant: 120),
gradView.heightAnchor.constraint(equalTo: gradView.widthAnchor),
gradView.centerXAnchor.constraint(equalTo: gradContainerView.centerXAnchor),
gradView.centerYAnchor.constraint(equalTo: gradContainerView.centerYAnchor),
tlLabel.centerXAnchor.constraint(equalTo: gradView.leadingAnchor, constant: 0.0),
blLabel.centerXAnchor.constraint(equalTo: gradView.leadingAnchor, constant: 0.0),
trLabel.centerXAnchor.constraint(equalTo: gradView.trailingAnchor, constant: 0.0),
brLabel.centerXAnchor.constraint(equalTo: gradView.trailingAnchor, constant: 0.0),
tlLabel.bottomAnchor.constraint(equalTo: gradView.topAnchor, constant: -2.0),
trLabel.bottomAnchor.constraint(equalTo: gradView.topAnchor, constant: -2.0),
blLabel.topAnchor.constraint(equalTo: gradView.bottomAnchor, constant: 2.0),
brLabel.topAnchor.constraint(equalTo: gradView.bottomAnchor, constant: 2.0),
tlLabel.topAnchor.constraint(equalTo: gradContainerView.topAnchor, constant: 4.0),
tlLabel.leadingAnchor.constraint(equalTo: gradContainerView.leadingAnchor, constant: 4.0),
brLabel.trailingAnchor.constraint(equalTo: gradContainerView.trailingAnchor, constant: -4.0),
brLabel.bottomAnchor.constraint(equalTo: gradContainerView.bottomAnchor, constant: -4.0),
])
view.addSubview(theStackView)
NSLayoutConstraint.activate([
theStackView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 40.0),
theStackView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
theButton.widthAnchor.constraint(equalToConstant: 160.0),
descLabel.widthAnchor.constraint(equalToConstant: 240.0),
])
theButton.addTarget(self, action: #selector(didTap(_:)), for: .touchUpInside)
idx = -1
didTap(nil)
}
@IBAction func didTap(_ sender: Any?) {
guard let gLayer = gradView.layer as? CAGradientLayer else {
fatalError("Could not get the gradient layer!")
}
idx += 1
if idx >= gradDefs.count {
idx = 0
}
let gDef = gradDefs[idx]
gLayer.type = gDef.gradType
gLayer.startPoint = gDef.startPoint
gLayer.endPoint = gDef.endPoint
var s = ""
s += "Gradient Type: " + (gDef.gradType == CAGradientLayerType.axial ? "Axial" : "Radial")
s += "\n\n"
s += "Start Point: \(gDef.startPoint)"
s += "\n"
s += "End Point: \(gDef.endPoint)"
if gDef.gradType == CAGradientLayerType.radial {
let w = abs(gDef.startPoint.x - gDef.endPoint.x) * 2
let h = abs(gDef.startPoint.y - gDef.endPoint.y) * 2
s += "\n\n"
s += "\t" + "Radial Width:"
s += "\n"
s += "\t\t" + "abs(\(gDef.startPoint.x) - \(gDef.endPoint.x)) * 2 == \(w)"
s += "\n\n"
s += "\t" + "Radial Height:"
s += "\n"
s += "\t\t" + "abs(\(gDef.startPoint.y) - \(gDef.endPoint.y)) * 2 == \(h)"
}
s += "\n"
descLabel.text = s
counterLabel.text = "Variation \(idx + 1) of \(gradDefs.count)"
}
}
一切都在代码中完成 - 没有@IBOutlets
或@IBActions
,所以只需创建一个新的视图控制器并将其自定义类分配给GradTestViewController
.
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