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ioscocoa-touch

iphone sdk CGAffineTransform getting the angle of rotation of an object

how do i calculate the angle of rotation for any given object (ie a uiimageview)?

Solution

  • Technically you can't, because the transform can include a skew operation which turns the image into a parallelogram and the rotation angle isn't defined anymore.

    Anyway, since the rotation matrix generates

     cos(x)  sin(x)   0
-sin(x)  cos(x)   0
   0        0     1

    You can recover the angle with

    return atan2(transform.b, transform.a);