仅从CGAffineTransform获取缩放转换 [英] Get just the scaling transformation out of CGAffineTransform

问题描述

我发现了一个关于仅获得旋转的类似问题，但是据我了解，缩放和旋转在变换矩阵中的工作有所不同.

I found a similar question about getting just the rotation, but as I understand scaling and rotating work different in the transform matrix.

矩阵不是我的强项，所以如果有人提示我如何从CGAffineTransform中获得仅缩放，我将不胜感激.

Matrixes are not my strength, so if anybody would hint me how to get only the scaling out of a CGAffineTransform I'd greatly appreciate.

顺便说一句.我尝试在CGSize上应用CGAffineTransform，然后获取height x width以查看其缩放比例，但是height x width具有奇怪的值(取决于CGAffineTransform中的旋转程度，所以... hm不起作用)

btw. I tried applying the CGAffineTransform on a CGSize and then get the height x width to see how much it scaled, but height x width have strange values (depending on the rotation found in the CGAffineTransform, so ... hm that does not work)

推荐答案

假设变换是缩放，然后是旋转(可能有平移，但没有倾斜)，则水平缩放因子为sqrt(a^2+c^2)，垂直比例因子为sqrt(b^2+d^2)，水平比例因子与垂直比例因子之比应为a/d = -c/b，其中a，b，c和d是六个成员中的四个根据文档中的CGAffineTransform(tx和ty仅代表翻译，这不会影响比例因子.

Assuming that the transformation is a scaling followed by a rotation (possibly with a translation in there, but no skewing) the horizontal scale factor is sqrt(a^2+c^2), the vertical scale factor is sqrt(b^2+d^2), and the ratio of the horizontal scale factor to the vertical scale factor should be a/d = -c/b, where a, b, c, and d are four of the six members of the CGAffineTransform, per the documentation (tx and ty only represent translation, which does not affect the scale factors).

|  a  b 0 |
|  c  d 0 |
| tx ty 1 |

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