Traditional Presentation Manager bounds are unclipped, and use a single rectangle to define their limits. In order to better define the bounding area, the DCAF-enabled display driver now has the ability to maintain one or more clipped, multirectangle regions (Screen Change Areas or SCAs) that are updated to indicate areas on the screen that have been drawn to.

This ability is provided by the following changes to the base driver:

• Three new entry points or functions to create, query and delete Screen Change Areas, as follows:

  • GreOpenScreenChangeArea

  • GreGetScreenChangeArea

  • GreCloseScreenChangeArea
  
  Two bounds accumulation internal routines, which add a single rectangle to all of the currently active SCAs.
  
  An extra flag test in the path of every display driver drawing function (for COM_SCR_BOUND in the high-order word in the last parameter of the GreXX calls, FunN).

  If this flag is set and the drawing operation is going to the screen, the drawing function passes a clipped bounding rectangle of the drawing primitive to the bounds accumulation functions described above. The code required to do this is driver-specific.

  
  Interception of Windows cursor exclusion calls and passing the supplied exclusion rectangle to the new bounds accumulation function.

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