ios - iOS 在两种颜色之间的点处查找颜色

Question

我有一个问题：我需要能够采用两种颜色并从中制作“虚拟渐变”。然后我需要能够在这条线上的任何点找到颜色。我目前的做法是这样的：

if (fahrenheit < kBottomThreshold)
{
    return [UIColor colorWithRed:kBottomR/255.0f green:kBottomG/255.0f blue:kBottomB/255.0f alpha:1];
}
if (fahrenheit > kTopThreshold)
{
    return [UIColor colorWithRed:kTopR/255.0f green:kTopG/255.0f blue:kTopB/255.0f alpha:1];
}

double rDiff = kTopR - kBottomR;
double gDiff = kTopG - kBottomG;
double bDiff = kTopB - kBottomB;

double tempDiff = kTopThreshold - kBottomThreshold;

double rValue;
double gValue;
double bValue;

rValue = kBottomR + ((rDiff/tempDiff) * fahrenheit);
gValue = kBottomG + ((gDiff/tempDiff) * fahrenheit);
bValue = kBottomB + ((bDiff/tempDiff) * fahrenheit);

return [UIColor colorWithRed:rValue/255.0f green:gValue/255.0f blue:bValue/255.0f alpha:1];

变量：

fahrenheit是传递给我的函数的变量，它是我要为其查找颜色的虚拟行上的数字。
kTopR, kTopB, 和kTopG是渐变一端的 RGB 值。他们的kBottom同行也一样。
kBottomThreshold并且kTopThreshold是我的渐变的端点。

这是我的问题： 当fahrenheit越过渐变的任一端时，渐变似乎“跳跃”到不同的值。

我在这里包含了一个托管在我的 S3 服务器上的示例项目。

您确实需要下载该项目并在模拟器/设备上尝试以了解我的意思（除非您非常聪明并且可以通过查看代码来判断）

score 35 · Accepted Answer

斯威夫特 - 3.0 && 4.0

extension UIColor {
    func toColor(_ color: UIColor, percentage: CGFloat) -> UIColor {
        let percentage = max(min(percentage, 100), 0) / 100
        switch percentage {
        case 0: return self
        case 1: return color
        default:
            var (r1, g1, b1, a1): (CGFloat, CGFloat, CGFloat, CGFloat) = (0, 0, 0, 0)
            var (r2, g2, b2, a2): (CGFloat, CGFloat, CGFloat, CGFloat) = (0, 0, 0, 0)
            guard self.getRed(&r1, green: &g1, blue: &b1, alpha: &a1) else { return self }
            guard color.getRed(&r2, green: &g2, blue: &b2, alpha: &a2) else { return self }

            return UIColor(red: CGFloat(r1 + (r2 - r1) * percentage),
                           green: CGFloat(g1 + (g2 - g1) * percentage),
                           blue: CGFloat(b1 + (b2 - b1) * percentage),
                           alpha: CGFloat(a1 + (a2 - a1) * percentage))
        }
    }
}

用法：-

let colorRed = UIColor.red
let colorBlue = UIColor.blue

let colorOutput = colorRed.toColor(colorBlue, percentage: 50)

结果

score 8 · Accepted Answer

问题是你没有kBottomThreshold从farenheit.

但是让我们简化一下。

首先，我们要将输入温度映射到t[0 ... 1] 范围内的参数。然后，我们想要映射t到范围 [ kBottomR... kTopR] 中的输出，也映射到范围 [ ... ] 中的输出，以及范围 [ kBottomG... kTopG] 中的输出。kBottomBkTopB

UIColor *colorForDegreesFahrenheit(double fahrenheit) {
    double t = (fahrenheit - kBottomThreshold) / (kTopThreshold - kBottomThreshold);

    // Clamp t to the range [0 ... 1].
    t = MAX(0.0, MIN(t, 1.0));

    double r = kBottomR + t * (kTopR - kBottomR);
    double g = kBottomG + t * (kTopG - kBottomG);
    double b = kBottomB + t * (kTopB - kBottomB);

    return [UIColor colorWithRed:r/255 green:g/255 blue:b/255 alpha:1];
}

score 6 · Accepted Answer

谢谢@ramchandra-n我实现了扩展以按百分比从颜色数组中获取中间颜色

extension Array where Element: UIColor {
    func intermediate(percentage: CGFloat) -> UIColor {
        let percentage = Swift.max(Swift.min(percentage, 100), 0) / 100
        switch percentage {
        case 0: return first ?? .clear
        case 1: return last ?? .clear
        default:
            let approxIndex = percentage / (1 / CGFloat(count - 1))
            let firstIndex = Int(approxIndex.rounded(.down))
            let secondIndex = Int(approxIndex.rounded(.up))
            let fallbackIndex = Int(approxIndex.rounded())
            
            let firstColor = self[firstIndex]
            let secondColor = self[secondIndex]
            let fallbackColor = self[fallbackIndex]
            
            var (r1, g1, b1, a1): (CGFloat, CGFloat, CGFloat, CGFloat) = (0, 0, 0, 0)
            var (r2, g2, b2, a2): (CGFloat, CGFloat, CGFloat, CGFloat) = (0, 0, 0, 0)
            guard firstColor.getRed(&r1, green: &g1, blue: &b1, alpha: &a1) else { return fallbackColor }
            guard secondColor.getRed(&r2, green: &g2, blue: &b2, alpha: &a2) else { return fallbackColor }
            
            let intermediatePercentage = approxIndex - CGFloat(firstIndex)
            return UIColor(
                red: CGFloat(r1 + (r2 - r1) * intermediatePercentage),
                green: CGFloat(g1 + (g2 - g1) * intermediatePercentage),
                blue: CGFloat(b1 + (b2 - b1) * intermediatePercentage),
                alpha: CGFloat(a1 + (a2 - a1) * intermediatePercentage)
            )
        }
    }
}

您可以使用它来获得两种或多种颜色之间的中间颜色：

let color = [.green, .yellow, .red].intermediate(percentage: 70)

score 4 · Accepted Answer

如果您的渐变比 2 色渐变更复杂，您可以考虑将 CGGradientRef 绘制到临时 CGImageRef 中并直接从图像缓冲区读取 RGBA 值。

这是我与 5 个渐变色标和颜色有关的事情：

    CGFloat tmpImagewidth = 1000.0f; // Make this bigger or smaller if you need more or less resolution (number of different colors).
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    // create a gradient
    CGFloat locations[] = { 0.0,
        0.35,
        0.55,
        0.8,
        1.0 };
    NSArray *colors = @[(__bridge id) [UIColor redColor].CGColor,
                        (__bridge id) [UIColor greenColor].CGColor,
                        (__bridge id) [UIColor blueColor].CGColor,
                        (__bridge id) [UIColor yellowColor].CGColor,
                        (__bridge id) [UIColor redColor].CGColor,
                        ];
    CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (__bridge CFArrayRef) colors, locations);
    CGPoint startPoint = CGPointMake(0, 0);
    CGPoint endPoint = CGPointMake(tmpImagewidth, 0);

    // create a bitmap context to draw the gradient to, 1 pixel high.
    CGContextRef context = CGBitmapContextCreate(NULL, tmpImagewidth, 1, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast);

    // draw the gradient into it
    CGContextAddRect(context, CGRectMake(0, 0, tmpImagewidth, 1));
    CGContextClip(context);
    CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0);

    // Get our RGB bytes into a buffer with a couple of intermediate steps...
    //      CGImageRef -> CFDataRef -> byte array
    CGImageRef cgImage = CGBitmapContextCreateImage(context);
    CGDataProviderRef provider = CGImageGetDataProvider(cgImage);
    CFDataRef pixelData = CGDataProviderCopyData(provider);

    // cleanup:
    CGGradientRelease(gradient);
    CGColorSpaceRelease(colorSpace);
    CGImageRelease(cgImage);
    CGContextRelease(context);

    const UInt8* data = CFDataGetBytePtr(pixelData);

    // we got all the data we need.
    // bytes in the data buffer are a succession of R G B A bytes

    // For instance, the color of the point 27% in our gradient is:
    CGFloat x = tmpImagewidth * .27;
    int pixelIndex = (int)x * 4; // 4 bytes per color
    UIColor *color = [UIColor colorWithRed:data[pixelIndex + 0]/255.0f
                                     green:data[pixelIndex + 1]/255.0f
                                      blue:data[pixelIndex + 2]/255.0f
                                     alpha:data[pixelIndex + 3]/255.0f];

    // done fetching color data, finally release the buffer
    CGDataProviderRelease(provider);

我并不是说这比上面答案中的“数学方式”更好，当然，生成临时图像会产生内存和 CPU 税。然而，这样做的好处是，无论您需要多少渐变停止，代码复杂性都保持不变......

score 2 · Accepted Answer

斯威夫特 5.3

获取两种颜色之间的 n 种颜色：

import UIKit

extension CGFloat {
    var getPercentageValues: [CGFloat] {
        let increment: CGFloat = 100/(self-1)
        var values = [CGFloat]()
        let last: CGFloat = 100
        var value: CGFloat = 0
        while value <= last {
            values.append(value)
            value += increment
        }
        return values
    }
}

extension UIColor {
    func toColor(_ color: UIColor, percentage: CGFloat) -> UIColor {
        let percentage = max(min(percentage, 100), 0) / 100
        switch percentage {
        case 0: return self
        case 1: return color
        default:
            var (r1, g1, b1, a1): (CGFloat, CGFloat, CGFloat, CGFloat) = (.zero, .zero, .zero, .zero)
            var (r2, g2, b2, a2): (CGFloat, CGFloat, CGFloat, CGFloat) = (.zero, .zero, .zero, .zero)
            guard self.getRed(&r1, green: &g1, blue: &b1, alpha: &a1) else { return self }
            guard color.getRed(&r2, green: &g2, blue: &b2, alpha: &a2) else { return self }
            
            return UIColor(red: CGFloat(r1 + (r2 - r1) * percentage),
                           green: CGFloat(g1 + (g2 - g1) * percentage),
                           blue: CGFloat(b1 + (b2 - b1) * percentage),
                           alpha: CGFloat(a1 + (a2 - a1) * percentage))
        }
    }
    
    func getColors(to color: UIColor, with quantity: CGFloat) -> [UIColor] { 
        quantity.getPercentageValues.map { self.toColor(color, percentage: $0 ) }
    }
}

let redColor = UIColor.red
let blueColor = UIColor.blue

print(redColor.getColors(to: blueColor, with: 10))

结果

score 1 · Accepted Answer

我想扩展/修改@Sebastien Windal 的答案，因为他的答案非常适合我的用例，但可以通过直接从上下文中获取 pixelData 来进一步改进（请参阅Get pixel data as array from UIImage/CGImage in swift）。

我迅速实现了他的答案，因此更改也用 swift 编写。

只需在绘制渐变之前将 Int Array 传递给上下文。然后，在绘制上下文时，该数组将用 pixelData 填充。

let dataSize = tmpImagewidth * 1 * 4
var pixelData = [UInt8](repeating: 0, count: Int(dataSize))


let context = CGContext(data: &pixelData, width: Int(tmpImagewidth), height: 1, bitsPerComponent: 8, bytesPerRow: 4 * Int(tmpImagewidth), space: colorSpace, bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)

然后我们可以先跳过创建图像，然后从那里读取 pixelData。

score 0 · Accepted Answer

SwiftUI 颜色运算符 + 重载

 func +(lhs: Color, rhs: Color) -> Color {
    let lhsUIColor = UIColor(lhs)
    let rhsUIColor = UIColor(rhs)
    
    var (r1, g1, b1, a1): (CGFloat, CGFloat, CGFloat, CGFloat) = (0, 0, 0, 0)
    var (r2, g2, b2, a2): (CGFloat, CGFloat, CGFloat, CGFloat) = (0, 0, 0, 0)
    guard lhsUIColor.getRed(&r1, green: &g1, blue: &b1, alpha: &a1) else { return Color(lhsUIColor) }
    guard rhsUIColor.getRed(&r2, green: &g2, blue: &b2, alpha: &a2) else { return Color(rhsUIColor) }

    return Color(Color.RGBColorSpace.sRGB, red: Double(r1 + r2) / 2, green: Double(g1 + g2) / 2, blue: Double(b1 + b2) / 2, opacity: Double(a1 + a2) / 2)
}

ios - iOS 在两种颜色之间的点处查找颜色

7 回答 7

斯威夫特 5.3

结果

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