Inside Macintosh: Apple Game Sprockets Guide /

Chapter 2 - DrawSprocket / DrawSprocket Reference

DrawSprocket Functions / Drawing and Double Buffering

DSpContext_InvalBackBufferRect

You can use the DSpContext_InvalBackBufferRect function to invalidate a specific area of a context's back buffer, so that only a portion of the screen needs to be redrawn when the buffers are next swapped.

OSStatus DSpContext_InvalBackBufferRect (
DSpContextReference inContext,
const Rect *inRect);

inContext

A reference to the context whose back buffer is to be invalidated.

inRect

A pointer to a rectangle specifying the area (in back-buffer coordinates) to invalidate.

function result

A result code.

DESCRIPTION

The DSpContext_InvalBackBufferRect function invalidates the area of the back buffer specified in the inRect parameter for the context specified in the inContext parameter. If you do not call this function between buffer swaps, the entire back buffer is considered invalid when a swap occurs. The invalid rectangles must be set prior to each call to DSpContext_SwapBuffers; the dirty rectangle list is emptied before DSpContext_GetBackBuffer returns the back buffer for re-use.

You can make multiple calls to this function between swaps to accumulate invalid rectangular areas. For information on the importance of using dirty rectangles, see "Improving Performance With Dirty Rectangles" (page 2-20).

CALLING RESTRICTIONS

Do not call this function during an interrupt.