Cannot preselect a custom paper format with QPrintDialog on Windows

There is no code in the Qt source tree to pre-populate the Windows DEVMODE structure for custom sizes.

In order to set a custom size the dmPaperSize field has to be set to DMPAPER_USER and the paper dimensions have to be specified in dmPaperWidth and dmPaperLength.

A grep on the source tree shows that these members are never used or accessed.

The attached program shows a print dialog with a preset custom format of 12cm x 15cm. The program shows the dialog using both Qt and Windows native calls. Please note that for testing a printer driver should be used that supports custom formats.