如何使用 CAGradientLayer 绘制渐变色轮?
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【中文标题】如何使用 CAGradientLayer 绘制渐变色轮?【英文标题】:How to draw a gradient color wheel using CAGradientLayer? 【发布时间】:2017-08-20 18:42:26 【问题描述】:我从这些链接中得到了一些参考——
What is the Algorithm behind a color wheel?
Math behind the Colour Wheel
Basic color schemes
How to fill a bezier path with gradient color
我已经了解了“HSV 色彩空间”的概念。但是我想在CAGradientLayer
的帮助下使用RGB绘制一个色轮。
这里是使用简单的RGB颜色数组和UIBezierPath
制作色轮的代码sn-p -
func drawColorWheel()
context?.saveGState()
range = CGFloat(100.00 / CGFloat(colorArray.count))
for k in 0 ..< colorArray.count
drawSlice(startPercent: CGFloat(k) * range, endPercent: CGFloat(CGFloat(k + 1) * range), color: colorArray.object(at: k) as! UIColor)
context?.restoreGState()
func drawSlice(startPercent: CGFloat, endPercent: CGFloat, color: UIColor)
let startAngle = getAngleAt(percentage: startPercent)
let endAngle = getAngleAt(percentage: endPercent)
let path = getArcPath(startAngle: startAngle, endAngle: endAngle)
color.setFill()
path.fill()
其中getAngleAt()
和getArcPath()
是用角度绘制路径的私有函数。
这是我的代码的最终输出 -
现在,我的问题是如何给这些颜色一个渐变效果,使每种颜色与渐变色层混合?
【问题讨论】:
【参考方案1】:一种方法是构建图像并手动操作像素缓冲区:
创建特定大小和特定类型的CGContext
;
通过data
属性访问其数据缓冲区;
将其重新绑定到可以轻松操作该缓冲区的东西(我使用Pixel
,struct
用于像素的 32 位表示);
逐个循环遍历像素,将其转换为该图像中圆圈的angle
和radius
;和
如果像素在圆圈内,则创建适当颜色的像素;如果不是,则将其设为零 alpha 像素。
所以在 Swift 3 中:
func buildHueCircle(in rect: CGRect, radius: CGFloat, scale: CGFloat = UIScreen.main.scale) -> UIImage?
let width = Int(rect.size.width * scale)
let height = Int(rect.size.height * scale)
let center = CGPoint(x: width / 2, y: height / 2)
let space = CGColorSpaceCreateDeviceRGB()
let context = CGContext(data: nil, width: width, height: height, bitsPerComponent: 8, bytesPerRow: width * 4, space: space, bitmapInfo: Pixel.bitmapInfo)!
let buffer = context.data!
let pixels = buffer.bindMemory(to: Pixel.self, capacity: width * height)
var pixel: Pixel
for y in 0 ..< height
for x in 0 ..< width
let angle = fmod(atan2(CGFloat(x) - center.x, CGFloat(y) - center.y) + 2 * .pi, 2 * .pi)
let distance = hypot(CGFloat(x) - center.x, CGFloat(y) - center.y)
let value = UIColor(hue: angle / 2 / .pi, saturation: 1, brightness: 1, alpha: 1)
var red: CGFloat = 0
var green: CGFloat = 0
var blue: CGFloat = 0
var alpha: CGFloat = 0
value.getRed(&red, green: &green, blue: &blue, alpha: &alpha)
if distance <= (radius * scale)
pixel = Pixel(red: UInt8(red * 255),
green: UInt8(green * 255),
blue: UInt8(blue * 255),
alpha: UInt8(alpha * 255))
else
pixel = Pixel(red: 255, green: 255, blue: 255, alpha: 0)
pixels[y * width + x] = pixel
let cgImage = context.makeImage()!
return UIImage(cgImage: cgImage, scale: scale, orientation: .up)
在哪里
struct Pixel: Equatable
private var rgba: UInt32
var red: UInt8
return UInt8((rgba >> 24) & 255)
var green: UInt8
return UInt8((rgba >> 16) & 255)
var blue: UInt8
return UInt8((rgba >> 8) & 255)
var alpha: UInt8
return UInt8((rgba >> 0) & 255)
init(red: UInt8, green: UInt8, blue: UInt8, alpha: UInt8)
rgba = (UInt32(red) << 24) | (UInt32(green) << 16) | (UInt32(blue) << 8) | (UInt32(alpha) << 0)
static let bitmapInfo = CGImageAlphaInfo.premultipliedLast.rawValue | CGBitmapInfo.byteOrder32Little.rawValue
static func ==(lhs: Pixel, rhs: Pixel) -> Bool
return lhs.rgba == rhs.rgba
产生:
或者您可以根据半径调整亮度或饱和度:
【讨论】:
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