Get just the scaling transformation out of CGAffineTransform

Question

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

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.

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)

Answer 1

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).

Answer 2

I have a similar problem trying to get the scaleX, scaleY, and rotation values out of a transformation. In my case, I have a UIImageView that I allow a user to scale, rotate, flip, in any order and multiple times. But I need to extract the scaleX, scaleY, and rotation values and store them in a database so the next time the user comes back, I can redraw the UIImageView in the same location with the same scale and rotation transformations that have been applied. If I just apply a transformation or two, I am successful, but once numerous transformations in random orders happen, the values get thrown off. Then I don't know which order to re-apply the transformations when I re-draw the object. Not sure if anyone else has any advice? Thanks.