Get size of UIView after applying CGAffineTransform

Question

I was surprised not to find an answer to this question, maybe is something very simple I somehow overlook :

How to get the real size of an UIView after I apply a CG

Answer 1

I use this in Objective C:

CGRect transformedBounds = CGRectApplyAffineTransform(view.bounds, view.transform);

or in Swift 4:

let transformedBounds = view.bounds.applying(view.transform)

Answer 2

Simpler: A view with (bounds) size s to which transform tr is applied has resulting size:

CGSizeMake(s.width*hypotf(tr.a, tr.b), s.height*hypotf(tr.c, tr.d))

However, if view's superview or any ancestor view has any non-unit transform applied, this size makes little sense in absolute terms.

If you want the absolute size of a view in window coordinates after any arbitrary transform has been applied to that view or its superviews, you should first compute the absolute transform matrix by composing all the view transform up to the root window, and then apply the above formula to the result.

Answer 3

Use CGSizeApplyAffineTransform(size, transform) and it will return a transformed size. There are similar CGPoint and CGRect functions as well.

Answer 4

Old question, but bumped into here, after searching a solution and tons of attempts. It was simple;

view.layer.frame has all transformations applied and you'll get the size from view.layer.frame.size easily.

-- below here is not an answer to this question - -

And for my problem, I was trying to calculate new center value after changing layer.anchorPoint of my rotated view, so it doesn't move. And finally did it like this;

CGPoint topLeft = [self.superview convertPoint:CGPointMake(0, 0) fromView:self];
self.layer.anchorPoint = CGPointMake(0, 0);
self.center = topLeft;

for reverse

CGPoint center = [self.superview convertPoint:CGPointMake(self.bounds.size.width / 2, self.bounds.size.height / 2) fromView:self];
self.layer.anchorPoint = CGPointMake(.5, .5);
self.center = center;

finally.

Answer 5

[myView frame] returns the frame of the view as seen by the parent, for layout and relative sizes. [myView bounds] returns the bounds of the view as seen by itself, for drawing. If you have transforms applied to multiple views, you can use convertRect: to or from a view.

Edit:

Maybe something like this.

CGRect rect = [view bounds];
CGPathRef path = CGPathCreateMutable();
rect.origin = CGPointZero;
CGPathAddRect( rect , [view transform] );
rect = CGPathGetBoundingBox( path );
CGPathRelease( path );

The use [view center] to find the position in the superview.

Answer 6

But you apply a rotating transform, it don't get right size by CGPathGetBoundingBox.