Normalising CGRect between 0 and 1

Question

What is the best way to normalise CGRect values so that they are between 0 and 1 (unit coordinate system)?

Answer 1

This should do the trick. You just need to divide everything by the width/height of the parent view or layer.

CGFloat parentWidth = parentView.bounds.size.width;
CGFloat parentHeight = parentView.bounds.size.height;

CGRect rectToConvert = ...;

rectToConvert.origin.x /= parentWidth;
rectToConvert.origin.y /= parentHeight;
rectToConvert.size.width /= parentWidth;
rectToConvert.size.height /= parentHeight;

We say these kinds of rects and points are in the "unit coordinate system". You can read more about it in the Core Animation Programming Guide.

Answer 2

How about this:

CGRect rectToConvert;
NSAffineTransform *n = [NSAffineTransform transform];
[n scaleXBy:rectToConvert.size.width 
        yBy:rectToConvert.size.height];
[n invert];

CGRect normalizedRect;
normalizedRect.origin = [n transformPoint:rectToConvert.origin];
normalizedRect.size   = [n transformSize: rectToConvert.size];

CGPoint anyPointINeedToConvert;
CGPoint convertedPoint = [n transformPoint:anyPointINeedToConvert];

I thinks this makes it a little clearer what's going on and lets you take care of translations in an obvious way, if you have to do them.

Answer 3

A very concise way of doing this would be:

CGAffineTransform t = CGAffineTransformMakeScale(1.0 / parentRect.size.width, 1.0 / parentRect.size.height);
CGRect unitRect = CGRectApplyAffineTransform(rect, t);