Control

The Control function carries out the device-specific extension specified by the wFunction parameter. GDI calls Control when an application calls the Escape function (GDI.38). For this reason, the device-specific extensions are also called escapes.

Every graphics driver must export a Control function.

Parameters

lpDestDev

Points to a PDEVICE structure specifying the destination device.

wFunction

Specifies the escape to carry out. Although the number of wFunction values and the meaning of each value depends on the driver, GDI reserves a number of values to specify predefined escapes. For more information about predefined escapes, see Chapter 11, “Graphics-Driver Escapes.”

lpInData

Points to escape-specific input data.

lpOutData

Points to escape-specific output data.

Return Value

The return value depends on the escape function specified by the wFunction parameter. In general, positive values indicate success, negative values indicate an error, and zero can indicate either an unimplemented escape or a general error condition.

Comments

The export ordinal for this function is 3.

The Control function should always return zero for escapes that are unimplemented or unrecognized. The function should return the number of bytes copied if it copies data to a buffer pointed to by the lpOutData parameter, or if the lpOutData parameter is NULL, it should return the size in bytes of the buffer it requires to copy data.

GDI modifies some escapes before calling the Control function.