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Updating Regions

Prior to Mac OS X, the Mac OS Toolbox relied on the concept of invalidating regions that needed updating. When a portion of a window needed updating, the Event Manager sent an update event to your application. Your application responded by calling the Window Manager function BeginUpdate, redrawing the region that needed updating and then calling EndUpdate to signal that you were finished with the update. By using BeginUpdate and EndUpdate, the Window Manager tracked the actual areas that needed updating and your drawing was clipped only to the areas that needed updating, thus optimizing performance. To achieve a similar functionality in Mac OS X, you use HIView. See “Updating Windows.”

In your QuickDraw application, you might have used region updating in conjunction with XOR to minimize the amount of drawing that needed to be done for animation or editing. Quartz does not support XOR, but it does support transparent windows. You create a transparent window, position it on top of your existing window, and then use the overlay to draw your animation or perform your text editing. When you’re done, you throw away the overlay and update the original window, if necessary. See “Using Overlay Windows,” which describes how to provide a selection rectangle (marching ants) around a user-selected shape and how to provide visual feedback when the user drags a selection.

If you need to handle the content in a scrolling rectangle, use HIView to create a scrolling view (see the function HIScrollViewCreate). This provides an easy way to display a scrollable image. You can simply embed an image view within the scroll view and the scroll view automatically handles the scrolling of the image. You don’t need to install handlers for live feedback, adjust scroller positions and sizes, or move pixels. See HIView Programming Guide and HIView Reference for more information.

Contents:

Updating Windows
Using Overlay Windows
Relevant Resources

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