Drawing in Quartz 2D
Quartz 2D expands the drawing functions associated with QuickDraw. The most notable difference is that Quartz 2D eliminates output device and resolution specificity.
The drawing model utilized by Quartz 2D is based on PDF specification 1.4. Drawing takes place using a Cartesian coordinate system, where text, vectors, or bitmap images are placed on a grid. However, drawing output is not sent directly to the output device. Quartz 2D uses graphics contexts, environments in which drawing takes place. Each graphics context defines how the drawing should be presented: in a window, sent to a printer, an OpenGL layer, or off-screen. Each context rasterizes the drawing at the desired resolution without altering the data that defines the drawing. Thus, contexts are the mechanism by which Quartz 2D employs resolution- and device-independence. For example, a window context may rasterize an object to the appropriate screen resolution to create actual graphics on the display. The same object can be sent to a printing context at a much higher resolution. This permits the same graphics commands to yield output on any device using the most appropriate resolution.
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