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CGRect, CGSize and CGPoint Functions

Posted on November 7, 2008 by John Muchow in C


With an understanding of C structures, and the definitions of CGRect, CGSize and CGPoint behind us, let’s look at a handful of functions for working with these structures.

CGRectMake and NSStringFromCGRect

With CGRectMake we can create a new CGRect structure. The rectangles below have differing starting points, however, each have a width and height of 100. The function NSStringFromCGRect returns a string object that defines the rectangle passed in as a parameter:

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CGRect rect1 = CGRectMake(100, 100, 100, 100);
CGRect rect2 = CGRectMake(190, 190, 100, 100);
 
NSLog(@"rect1: %@", NSStringFromCGRect(rect1));
NSLog(@"rect2: %@", NSStringFromCGRect(rect2));

Note : The output of all examples are shown in the image at the bottom of this post.

CGRectIntersect

To determine if two rectangles intersect, you can write code as follows:

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CGRect rect3 = CGRectMake(100, 100, 100, 100);
CGRect rect4 = CGRectMake(190, 190, 100, 100);
 
if (CGRectIntersectsRect(rect3, rect4) == 1)
  NSLog(@"The rectangles intersect");
else
  NSLog(@"The rectangles do not intersect");    
 
NSLog(@"rect3: %@", NSStringFromCGRect(rect3));
NSLog(@"rect4: %@", NSStringFromCGRect(rect4));

CGRectInset

If you need to create a rectangle that is either larger or smaller than an existing rectangle, centered on the same point, try CGRectInset:

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CGRect rect5 = CGRectMake(100, 100, 100, 100);
// Use positive values for a smaller rectangle
CGRect rect6 = CGRectInset(rect, 25, 25);
 
NSLog(@"%rect5: %@", NSStringFromCGRect(rect5));
NSLog(@"%rect6: %@", NSStringFromCGRect(rect6));
 
...
 
CGRect rect7 = CGRectMake(100, 100, 100, 100);
// Use negative values for a larger rectangle
CGRect rect8 = CGRectInset(rect, -25, -25);
 
NSLog(@"rect7: %@", NSStringFromCGRect(rect7));
NSLog(@"rect8: %@", NSStringFromCGRect(rect8));

CGRectFromString

A little more uncommon, is creating rectangles from a string, however, if the need arises:

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NSString *str = @"{{0,0},{50,50}}";
CGRect rect9 = CGRectFromString(str);
NSLog(@"rect9: %@", NSStringFromCGRect(rect9));

Functions for CGSize and CGPoint

As you would expect, there are similar functions to those above for working with CGSize and CGPoint:

  • CGSizeMake
  • CGSizeEqualToSize
  • CGPointMake
  • CGPointEqualToPoint

The output for the above code examples follows:

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