![]() ![]() The preferred method to handle vertical blanking is to have the display driver, when it first loads, set up a vertical blanking interrupt on your system bus. Tearing depends on whether your display hardware is able to send an interrupt for the vertical blanking period. This process, called tearing, prevents a partial view your new display surface from appearing while the previous surface is still being drawn. Just as with the primary surface, you should flip between overlay surfaces during the vertical blanking period. You expose the information in this DDHAL_DDSURFACECALLBACKS structure when you prepare your DDHALINFO structure in your implementation of HALInit. Specifically, your driver must set the DDHAL_SURFCB32_FLIP and DDHAL_SURFCB32_UPDATEOVERLAY flags and provide implementations for the Flip and UpdateOverlay functions. To let DirectDraw applications know that your driver supports overlay flipping, you must prepare a DDHAL_DDSURFACECALLBACKS structure by setting the capability bits and by specifying your driver's implementations of the DirectDraw surface management functions. To implement overlay flipping, your display hardware must have enough video memory to support as many overlay back buffers as you need for your overlay's flipping chain. Overlay surfaces must always be stored in video memory. The driver acts as an intermediary between the middleware and the DAC, correctly exposing the hardware's capabilities to the DirectDraw middleware and also managing the flow of data to the graphics hardware. The digital-to-analog converter (DAC) within the graphics hardware handles the composition of the primary and overlay surfaces. The DirectDraw middleware provides the infrastructure to maintain display surfaces support and allow flipping between them. For more information, see Flipping Surfaces, Overlay Surface Overview, and Flipping Overlay Surfaces. Applications can combine these two capabilities within DirectDraw to flip overlay surfaces just as they can with primary display surfaces. 该文转自msdn (v=winembedded.60).aspx The DirectDraw API provides support for both surface flipping and for overlay surfaces. ![]()
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