Programming iOS 6, 3rd Edition

Paths and Drawing

By issuing a series of instructions for moving an imaginary pen, you trace out a path. Such a path does not constitute drawing! First you provide a path; then you draw. Drawing can mean stroking the path or filling the path, or both. Again, this should be a familiar notion from certain drawing applications.

A path is constructed by tracing it out from point to point. Think of the drawing system as holding a pen. Then you must first tell that pen where to position itself, setting the current point; after that, you issue a series of commands telling it how to trace out each subsequent piece of the path. Each additional piece of the path starts at the current point; its end becomes the new current point.

Here are some path-drawing commands you’re likely to give:

Position the current point

CGContextMoveToPoint

Trace a line

CGContextAddLineToPoint, CGContextAddLines

Trace a rectangle

CGContextAddRect, CGContextAddRects

Trace an ellipse or circle

CGContextAddEllipseInRect

Trace an arc

CGContextAddArcToPoint, CGContextAddArc

Trace a Bezier curve with one or two control points

CGContextAddQuadCurveToPoint, CGContextAddCurveToPoint

Close the current path

CGContextClosePath. This appends a line from the last point of the path to the first point. There’s no need to do this if you’re about to fill the path, since it’s done for you.

Stroke or fill the current path

CGContextStrokePath, CGContextFillPath, CGContextEOFillPath, CGContextDrawPath. Stroking or filling ...