Applications can now modify printer settings (that is, DEVMODE values) while printing a document. The ResetDC function lets applications update the printer device context at each new page. This means applications can print documents containing a mixture of page orientations, paper sources, and other printing options without having to divide the document into smaller documents.
To support ResetDC, a printer driver must provide code for the RESETDEVICE escape. This escape, processed by the driver's Control function, copies printer output state information from one physical device context (PDEVICE) to another. GDI uses the escape to replace existing device contexts with new ones.
When an application calls ResetDC, GDI first creates a new PDEVICE by calling the driver's Enable function. This new PDEVICE receives the new printer settings as specified by the application. GDI next uses the RESETDEVICE escape to copy output state information from the existing PDEVICE to the new one. The output state includes information such as job number and list of downloaded fonts. The escape must copy the state information without changing the printer settings in the new PDEVICE. Finally, GDI substitutes the new PDEVICE for the old one in the application's device context, discarding the old PDEVICE by calling the Disable function.
When the printer driver receives the RESETDEVICE request, it must expect a subsequent call to Disable with no intervening call to the ENDDOC escape. The printer driver must also ensure that the new printer settings take affect starting on the next printed page. If a printer driver allocated bitmap or working buffers when it received the STARTDOC escape, the driver should free the buffers for the old PDEVICE and allocate new buffers for the new PDEVICE (an option is to reallocate the buffers).
The ResetDC function cannot be used to change the driver name, device name, or the output port. When the user physically changes port connection or the device name, the application must delete the original device context and recreate a device context with the new device name and output port. Also the application must cancel the selection of all objects in its device context before calling ResetDC.