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Drawing Destinations

In Quartz, all drawing takes place in a drawing environment called a graphics context. You can think of a graphics context as being equivalent to a QuickDraw grafport. Graphics contexts are really drawing destinations that are preconfigured for a specific use, including drawing to a window or printer, creating PDF content, creating a bitmap, drawing to an OpenGL context, or drawing to an offscreen layer. Some graphics contexts are multipaged, such as PDF and printing contexts. Every graphics context has a graphics state stack that you can use to save snapshots of the current drawing state. This allows you to modify the drawing state and then return back to a previous state.

Although graphics contexts are specialized for different drawing destinations, Quartz is designed to make as few assumptions as possible about the output device. For example, the Print Preview feature in Mac OS X redirects your output from a printing context to a PDF document and then to a raster display, with no loss of information or quality. This means that you simply draw to user space and let Quartz convert those coordinates appropriately for the graphics context.

Before you perform any drawing in Quartz, you need to obtain a graphics context because most drawing functions operate on a graphics context; that’s where your drawing is directed. Quartz provides creation functions for bitmap graphics contexts, PDF graphics contexts, OpenGL graphics contexts, and layers (which are derived from a graphics context, described in CGLayer Drawing in Quartz 2D Programming Guide).

You obtain graphics contexts that are used for drawing to windows or a printer from the appropriate framework. Carbon (HIView) and Cocoa provide window graphics contexts. See Creating a Window Graphics Context in Quartz 2D Programming Guide.

The Printing framework manages printing graphics contexts. In Mac OS X v10.4, you use the printing functions PMSessionBeginCGDocument and PMSessionGetCGGraphicsContext. Prior to Mac OS X v10.4 you use PMSessionSetDocumentFormatGeneration passing the constant kPMGraphicsContextCoreGraphics. See Obtaining a Graphics Context for Printing in Quartz 2D Programming Guide.

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