如何知道是否在 Xcode 中触摸了 .png 的唯一可见区域 [英] How to know that if the only visible area of a .png is touched in Xcode

问题描述

我已经在 Xcode 中的 UIImageView 中导入了一个 .png 图像，我想做的是当图像被触摸时，它将被隐藏.

I have imported a .png image into UIImageView in Xcode and what I want to make is when the image is touched, it will be hidden.

但我的问题是 png 图像包含透明部分，当我触摸透明部分时，动作会继续.我希望仅在触摸图像的可见部分时才进行操作.如何解决问题?

But my problem is that the png image contains transparent parts and when I touch on the transparent parts, the action goes on. I want the action to go on only when the visible part of the image is touched. How to solve the problem?

Swift 或 Objective-C

Swift or Objective-C

推荐答案

我创建了一个自定义 UIButton 子类，它的行为与您描述的完全一样，看看:https://github.com/spagosx/iOS-Shaped-Button-Swift

I have created a custom UIButton subclass that behaves exactly as you describe, have a look: https://github.com/spagosx/iOS-Shaped-Button-Swift

它是用 Swift 编写的，但很容易转换为 Objective-c.

It's written in Swift, but it's easily convertible to Objective-c.

方法是从触摸点获取像素数据并访问 RGBA 值，在这种情况下，我们读取 A (alpha) 并检查它是否高于我们的阈值.

The approach is to get the pixel data from the touch point and to access the RGBA values, in this case we read A (alpha) and check if it is higher than our threshold.

看一点代码:

func alphaFromPoint(point: CGPoint) -> CGFloat {
    var pixel: [UInt8] = [0, 0, 0, 0]
    let colourSpace = CGColorSpaceCreateDeviceRGB()
    let alphaInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue)
    let context = CGContext(data: &pixel, width: 1, height: 1, bitsPerComponent: 8, bytesPerRow: 4, space: colourSpace, bitmapInfo: alphaInfo.rawValue)

    context?.translateBy(x: -point.x, y: -point.y)

    self.layer.render(in: context!)

    let floatAlpha = CGFloat(pixel[3])
    return floatAlpha
}

您可以将 floatAlpha 值与您可接受的 alpha 值进行比较:

You can than take the floatAlpha value and compare it with your acceptable value of alpha:

    override func pointInside(point: CGPoint, withEvent event: UIEvent?) -> Bool {
        return self.alphaFromPoint(point) >= 100
    }

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