4 - Points, Sizes and Rectangles

The GNUstep base library defines some useful structs for dealing with two dimensional geometry: NSPoint, NSSize and NSRect. It is worth to quickly review them here, before beginning.

4.1 NSPoint

A NSPoint is defined as a struct with two members, the x and y coordinate of the point:

typedef struct _NSPoint
{
  float x;
  float y;
} NSPoint;

So, to access the x and y coordinates of a NSPoint called myPoint, you just do as in myPoint.x and myPoint.y. Please note that the coordinates of a NSPoint are floats; so, they might be negative and/or fractionary.

To create a point with given x and y coordinates, you can use the function (macro) NSMakePoint (), as in the following example:

NSPoint testPoint;

testPoint = NSMakePoint (10, 20);
NSLog (@"x coordinate: %f", testPoint.x); // 10
NSLog (@"y coordinate: %f", testPoint.y); // 20

It might be worth quoting the (predefined) constant NSZeroPoint, which is a point with zero x coordinate and zero y coordinate.

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4.2 NSSize

An NSSize is a struct describing the size of a rectangle, regardless of its position.

typedef struct _NSSize
{
  float width;
  float height;
} NSSize;

Using NSSize is completely analogous to using NSPoint, as in the following code example:

NSSize testSize;

testSize = NSMakeSize (0.5, 51);
NSLog (@"x coordinate: %f", testSize.width); // 0.5
NSLog (@"y coordinate: %f", testSize.height); // 51

NSZeroSize is a constant equal to a size with zero width and zero height.

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4.3 NSRect

An NSRect is a struct describing both the position and the size of a rectangle:

typedef struct _NSRect
{
  NSPoint origin;
  NSSize size;
} NSRect;

Using NSRect is similar to using NSPoint and NSSize:

NSRect testRect;

testRect = NSMakeRect (8.1, -3, 10, 15);
NSLog (@"x origin: %f", testRect.origin.x); // 8.1
NSLog (@"y origin: %f", testRect.origin.y); // -3
NSLog (@"width: %f", testRect.size.width); // 10
NSLog (@"height: %f", testRect.size.height); // 15

Note that you first access the origin, and then its coordinates, and similarly for the size.

The constant NSZeroRect represents a rect with NSZeroPoint origin and NSZeroSize size.

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4.4 Geometry Functions

The GNUstep base library provides functions and macros to do all the most common geometry operations on NSPoints, NSSizes and NSRects (such as determining if a point is contained in a rectangle, computing the intersection of two rectangles, etc). It would be off topic to discuss them here; please refer to the base library documentation whenever you need to do some of these common geometrical operations.

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