如何重置以标识“当前变换矩阵”有一些CGContext函数？ [英] How to reset to identity the "current transformation matrix" with some CGContext function?

问题描述

我在CTM上做了一系列翻译和旋转，在某些时候，我需要重置它以进行身份​​验证，然后再进行转换。

I'm doing a series of translations and rotations on the CTM and at some point I need to reset it to identity before going further with transformations.

（显然，应该有一个名为CGContextSetCTM的函数），因为效率是关键，我不想使用CGContextSaveGState / CGContextRestoreGState ...

I can't find any proper way to do it (obviously, there should have been a function named CGContextSetCTM or so) and since efficiency is the key, I don't want to use CGContextSaveGState/CGContextRestoreGState...

推荐答案

通过 CGContextGetCTM ，将其转换为 CGAffineTransformInvert ，并将当前矩阵乘以倒数（这很重要！）与 CGContextConcatCTM 。 CTM现在是身份。

Get current transformation matrix via CGContextGetCTM, invert it with CGAffineTransformInvert and multiply the current matrix by the inverted one (that's important!) with CGContextConcatCTM. CTM is now identity.

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