Cocoa in a Nutshell

Working with Paths

Drawing lines is the most basic function you can perform with Cocoa’s drawing classes. The Application Kit encapsulates the low-level, Quartz path-based drawing API in the NSBezierPath class. Minimally, NSBezierPath lets you draw straight lines and Bezier paths, and using this functionality, you can construct any shape you like.

Tip

Bezier curves, or paths, are curved lines based on the mathematics of third-degree polynomials. Because Bezier paths are based on equations, they are resolution-independent and can be scaled to any size without the loss of detail or quality generally experienced with bitmapped graphics.

Drawing with NSBezierPath is in some respects similar to drawing on a sheet of paper with a pencil. Before you can draw a line, you have to place the pencil lead at a point on the page. Drawing a line requires moving the pencil from one point to another. To draw a disjointed line, you pick up the pencil tip from the paper and move it to another location. You might then complete a diagram by drawing a line back to the first point. These actions are reflected in the following NSBezierPath methods, used to construct a path:

• moveToPoint:

• lineToPoint:

• curveToPoint:controlPoint1:controlPoint2:

• closePath

The arguments to the first three methods are all of type NSPoint, a C structure that encapsulates a coordinate pair. Example 4-1 shows the struct declaration for NSPoint.

Example 4-1. The NSPoint struct

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