Building Cocoa Applications: A Step by Step Guide

Quartz Graphics Data Types

As we discussed earlier, the Application Kit defines a number of data types and structures that are useful for drawing with Quartz. These data types are defined in the file NSGeometry.h, and we’ll describe some of them in this section.

Any point on the computer’s screen is defined by an NSPoint structure:

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

An extent in space is defined by an NSSize structure:

typedef struct _NSSize {
    float width;             // should never be negative
    float height;            // should never be negative
} NSSize;

Conveniently, a rectangle, NSRect, is defined by an extent from a point:

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

Cocoa defines a number of inline functions for creating and managing these structures. The code for an inline function is integrated directly into the code for its callers, so there is no function call overhead associated with using them. These functions allow you to create an unnamed structure that is used as an argument in a function call or method invocation and then destroyed. The functions are:

NSPoint NSMakePoint(float x, float y)
NSSize  NSMakeSize(float w, float h)
NSRect  NSMakeRect(float x, float y, float w, float h)

There are also a number of convenience functions in Cocoa, which are summarized in Table 14-1.

Table 14-1. Convenience graphics functions

Graphics function	Purpose
float NSMaxX(aRect)	Returns the maximum X coordinate (the right side) of the rectangle
float NSMaxY(aRect ...