如何在Swift中应用多个转换 [英] How to apply multiple transforms in Swift

问题描述

我想将多个转换应用于 UIView （或 UIView 的子类），例如translate，旋转和缩放。我知道，两个变换可以与 CGAffineTransformConcat ，但如果我有三个或更多变换，我该怎么办？

我见过这些问题：

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  感谢

  
  
  

  参见

  
  
  
  
  
  • CGAffineTransform Reference （docs）
  
  
  • 转换（docs）
  
  
  • Swift：翻译和旋转C GContext，一个视觉解释（iOS / Xcode）
  
  
  • 揭秘CGAffineTransform
  
  
  
  
  

  此答案已通过Swift 4测试

  
  

  I would like to apply multiple transforms to a UIView (or subclass of UIView), such as translate, rotate, and scale. I know that two transforms can be applied with CGAffineTransformConcat, but how do I do it if I have three or more transforms?

  I have seen these questions:

  • Applying multiple transforms to a UIView / CALayer
  • Using Multiple CGAffineTransforms On Text Matrix

  but these questions are asking something different, and the given answers just talk about applying two transforms with CGAffineTransformConcat. Also, they use Objective-C rather than Swift.

  解决方案

  You can apply multiple transforms by stacking them on top of each other.

  var t = CGAffineTransform.identity
  t = t.translatedBy(x: 100, y: 300)
  t = t.rotated(by: CGFloat.pi / 4)
  t = t.scaledBy(x: -1, y: 2)
  // ... add as many as you want, then apply it to to the view
  imageView.transform = t
  

  Or more compactly (but not necessarily as readable):

  imageView.transform = CGAffineTransform.identity.translatedBy(x: 100, y: 300).rotated(by: CGFloat.pi / 4).scaledBy(x: -1, y: 2)
  

  This series of transforms produces the image on the right:

  Thanks to this answer for teaching me how to do it.

  Notes

  • The order in which you apply the transforms matters. For example, if the transforms were done in the opposite order it would produce the following result.

    t = t.scaledBy(x: -1, y: 2)
    t = t.rotated(by: CGFloat.pi / 4)
    t = t.translatedBy(x: 100, y: 300)
    

  See also

  • CGAffineTransform Reference (docs)
  • Transforms (docs)
  • Swift: Translating and Rotating a CGContext, A Visual Explanation (iOS/Xcode)
  • Demystifying CGAffineTransform

  This answer has been tested with Swift 4

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