Check if CGRect is contained within another (transformed) rect

Question

I'm implementing a cropping feature and I'm trying to figure out how to test whether the crop rectangle is fully contained within the transformed image view. i.e. there should be no whitespace in the cropped portion of the image.

I've tried to copy the behavior as implemented in this component: https://github.com/heitorfr/ios-image-editor, which implements a similar check (see below), but I can't get it to work for my situation.

- (void)checkBoundsWithTransform:(CGAffineTransform)transform
{
    CGRect r1 = [self boundingBoxForRect:self.preview.cropRect 
                        rotatedByRadians:[self imageRotation]];
    Rectangle r2 = [self applyTransform:transform 
                                 toRect:self.preview.initialImageFrame];

    CGAffineTransform t = 
     CGAffineTransformMakeTranslation(CGRectGetMidX(self.preview.cropRect), 
                                      CGRectGetMidY(self.preview.cropRect));
    t = CGAffineTransformRotate(t, -[self imageRotation]);
    t = CGAffineTransformTranslate(t, 
                                   -CGRectGetMidX(self.preview.cropRect), -
                                   CGRectGetMidY(self.preview.cropRect));

    Rectangle r3 = [self applyTransform:t toRectangle:r2];

    if(CGRectContainsRect([self CGRectFromRectangle:r3],r1)) {
        self.validTransform = transform;
    }
}

possible duplicate of [CGRectContainsRect Not Working](http://stackoverflow.com/questions/8981931/cgrectcontainsrect-not-working) — Palpatim, Apr 23 '14 at 14:52
this isn't an issue that can be solved with CGRectContainsRect(), because the transformed rect of the image view can be rotated. i.e. it can't be expressed with a CGRect — Niels, Apr 23 '14 at 15:01

score 1 · Accepted Answer · edited Apr 23 '14 at 15:45

1

Not the most performant solution, but very quick and dirty-ish.

NSBezierPath *path = [NSBezierPath bezierPathWithRect:r2];
[path transformUsingAffineTransform:t];
if([path containsPoint:NSMinX(r1)] 
    && [path containsPoint:NSMinY(r1)] 
    && [path containsPoint:NSMaxX(r1)] 
    && [path containsPoint:(NSMaxY(r1)] ){
    self.validTransform = transform;
}

edited Apr 23 '14 at 15:45

Alex Cio

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answered Apr 23 '14 at 15:44

lead_the_zeppelin

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I hadn't thought of using a NSBezierPath (or UIBezierPath in my case). good idea, thanks! – Niels Apr 23 '14 at 16:41

Check if CGRect is contained within another (transformed) rect

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