在UIScrollView（Swift 3）中滚动图像时背景颜色淡入淡出效果

Question

我在UIScrollView中有很多图像，其中我已经计算了图像的平均颜色，但是当我滚动时，我希望背景颜色（平均颜色）从一种颜色淡入下一种颜色通过图像。这就是我想要的（当我在ebay上滚动图像时注意背景颜色效果）： https://drive.google.com/file/d/0B3fFlkF0j7y9VDVycTg3aklCbDg/view

目前为止的源文件： https://www.dropbox.com/s/uw874rb8r9ytzrg/TestApp.zip?dl=0

任何帮助都将不胜感激。

Answer 1

  func fade(fromRed: CGFloat,
              fromGreen: CGFloat,
              fromBlue: CGFloat,
              fromAlpha: CGFloat,
              toRed: CGFloat,
              toGreen: CGFloat,
              toBlue: CGFloat,
              toAlpha: CGFloat,
              withPercentage percentage: CGFloat) -> UIColor {

    let red: CGFloat = (toRed - fromRed) * percentage + fromRed
    let green: CGFloat = (toGreen - fromGreen) * percentage + fromGreen
    let blue: CGFloat = (toBlue - fromBlue) * percentage + fromBlue
    let alpha: CGFloat = (toAlpha - fromAlpha) * percentage + fromAlpha

    // return the fade colour
    return UIColor(red: red, green: green, blue: blue, alpha: alpha)
}