Calculating a Relative Angle
Screen reorientation support means that an interface’s relationship to a given device angle must be supported in quarters, one for each possible front-facing screen orientation. As the UIViewController automatically rotates its onscreen view, the math needs to catch up to account for those reorientations.
The following method, which is written for use in a UIDevice category, calculates angles so that the angle remains in synchrony with the device orientation. This creates simple offsets from vertical that match the way the GUI is currently presented:
- (float)orientationAngleRelativeToOrientation: (UIDeviceOrientation)someOrientation { float dOrientation = 0.0f; switch (someOrientation) ...
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