Recipe: Drawing Touches Onscreen
UIView hosts the realm of direct onscreen drawing. Its drawRect: method offers a low-level way to draw content directly, letting you create and display arbitrary elements using Quartz 2D calls. With touch and drawing, you can build concrete, manipulatable interfaces.
Recipe 1-7 combines gestures with drawRect to introduce touch-based painting. As a user touches the screen, the TouchTrackerView class builds a Bezier path that follows the user’s finger. To paint the progress as the touch proceeds, the touchesMoved:withEvent: method calls setNeedsDisplay. This, in turn, triggers a call to drawRect:, where the view strokes the accumulated Bezier path. Figure 1-3 shows the interface with a path created in this way. ...
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