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PDEV Negotiation

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One of the primary responsibilities of any graphics driver is to enable a PDEV during driver initialization. A PDEV is a logical representation of the physical device. This representation is defined by the driver and is typically a private data structure. Refer to DrvEnablePDEV for more information about enabling PDEVs.

Through the DrvEnablePDEV function, the driver must provide information to GDI that describes the requested device and its capabilities. One piece of important information that the driver gives GDI is the set of graphics capability flags (GCAPS_Xxx and GCAPS2_Xxx flags) in the flGraphicsCaps and flGraphicsCaps2 members of the DEVINFO structure.

The capability flags allow GDI to determine which operations the PDEV supports. For example, GDI tests the capability flags that indicate whether the PDEV can handle Bezier curves and geometric wide lines before GDI attempts to call the DrvStrokePath function to draw paths with these primitive types. If the capability flags indicate that the PDEV cannot handle these primitive types, GDI will break down the lines or curves so it can make simpler calls to the driver.

From the driver's side, whenever the driver gets an advanced path-related call from GDI, it can return FALSE if the path or clipping is too complex for the device to process.

The driver cannot return FALSE from DrvStrokePath when handling a cosmetic line because the driver must handle any complex clipping or styling for cosmetic lines. However, DrvStrokePath can return FALSE if the path has Bezier curves or geometric lines. When this occurs, GDI breaks the call down to simpler calls, just as it does if the capability bits are not set. For example, if DrvStrokePath returns FALSE when it is sent a geometric line, GDI simplifies the line and calls the DrvFillPath function.

If DrvStrokePath is to report an error, it must return DDI_ERROR.

This kind of negotiation between GDI and the driver, for functions that depend on the PDEV, permits GDI and the driver to produce high quality output without excess communication.