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，将其转换为，并将当前矩阵乘以倒数（这很重要！）与。 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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