This function displays a dialog box that allows the user to select a font, its
attributes (bold, italic, underline, strikeout) and its colour. This becomes
the font for the current drawing surface. RBGCOLOUR is used for both
input and output. On input it is the colour that is initially selected in the
dialog box. On output it is the RGB value selected by the user.
If this font is to be restored after a change of font then you should call
GET_FONT_ID@ before the change and then SELECT_FONT_ID@ to restore the font.