Presentation drivers support the error strategy implemented by the Presentation Manager interface. When an error occurs, the driver calls WinSetErrorInfo (see WinSetErrorInfo) to log the appropriate error code and set the return code to show that an error was detected.

The component that implements a function must provide error checking for the environment, objects, and resources associated with it. The presentation driver requires the following error checking:

• Fail-safe on routines that set attributes and transformation values. Any routine that changes attributes or transformation values must be able to restore the initial values if an error occurs during the change.

• Full error checking on symbol sets, fonts, bit maps, and regions.

• With segment drawing, drawing primitives, and primitive attributes in draw mode, unchecked parameters are passed directly to the graphics engine or the presentation driver. When one of these functions is hooked by the presentation driver, the handling routine must perform the necessary error checking and log any errors, or reset any invalid values to their defaults, as appropriate.

• For any function with coordinates as parameters, the presentation driver must check that the values passed are valid. When an invalid coordinate is detected, the handling routine must log an error or use a default coordinate value, as appropriate.

For any defined error, the application sees the same error code regardless of whether the error was logged by the Graphics Programming Interface (GPI), graphics engine, or presentation driver.