如何使用CAGradientLayer绘制渐变色轮？

I got some reference from these links-

我从这些链接中得到了一些参考 -

What is the Algorithm behind a color wheel?

色轮背后的算法是什么?
Math behind the Colour Wheel

色轮背后的数学
Basic color schemes

基本配色方案
How to fill a bezier path with gradient color

如何使用渐变颜色填充贝塞尔曲线路径

I have gone through the concept of "HSV colour space". But I want to draw a color wheel using RGB with the help of CAGradientLayer.

我已经经历了“HSV色彩空间”的概念。但我想在CAGradientLayer的帮助下使用RGB绘制色轮。

Here is the code snippet of making a color wheel by using simple RGB color array and UIBezierPath -

这是使用简单的RGB颜色数组和UIBezierPath制作色轮的代码片段 -

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()
}

Where getAngleAt() and getArcPath() are the private functions to draw the path with an angle.

其中getAngleAt()和getArcPath()是用角度绘制路径的私有函数。

Here is the final output of my code -

这是我的代码的最终输出 -

Now, my question is the how to give these colors a gradient effect so that each colors mix up with gradient color layer?

现在,我的问题是如何为这些颜色提供渐变效果,以便每种颜色与渐变颜色层混合?

1 个解决方案

#1

One approach is to build an image and manipulate the pixel buffer manually:

一种方法是构建图像并手动操作像素缓冲区:

Create CGContext of certain size and certain type;

创建一定大小和特定类型的CGContext;

Access its data buffer via data property;

通过数据属性访问其数据缓冲区;

Rebind that to something that makes it easy to manipulate that buffer (I use a Pixel, a struct for the 32-bit representation of a pixel);

将其重新绑定到可以轻松操作缓冲区的东西(我使用Pixel,一个用于像素的32位表示的结构);

Loop through the pixels, one by one, converting that to an angle and radius for the circle within this image; and

逐个循环通过像素,将其转换为此图像中圆圈的角度和半径;和

Create a pixel of the appropriate color if it's inside the circle; make it a zero-alpha pixel if not.

如果它在圆圈内,则创建一个适当颜色的像素;如果不是,则将其设为零alpha像素。

So in Swift 3:

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)
}

Where

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
    }
}

That yields:

Or you can tweak the brightness or saturation based upon the radius:

或者您可以根据半径调整亮度或饱和度:

#1