NAME
        PRD_DUMPRPORTTAGS -- dump the specified rastport to a printer (v44)

   FUNCTION
        Print a rendition of the supplied rastport, using the supplied
        colormap, position and scaling information, as specified in
        the printer preferences.

   IO REQUEST
        io_Message      mn_ReplyPort set if quick I/O is not possible.
        io_Command      prd_dumprport.
        io_Flags        IOB_QUICK set if quick I/O is possible.
        io_RastPort     ptr to a rastport.
        io_ColorMap     ptr to a colormap.
        io_Modes        the 'modes' flag from a viewport structure,
                        (the upper word is reserved and should be zero).

                        If you are running under version 36, or greater
                        of graphics.library, it is recommended that
                        you fill in "io_Modes" with the ULONG (32-bit)
                        value returned from calling:

                        ULONG ModeID = GetVPModeID(struct viewport *);

                        Doing so provides for upwards compatability with
                        the new display modes available under V36
                        (example: aspect ratio calculations for new
                        display modes).

        io_SrcX         x offset into the rastport to start printing from.
        io_SrcY         y offset into the rastport to start printing from.
        io_SrcWidth     width of the rastport to print (from io_srcx).
        io_SrcHeight    height of the rastport to print (from io_srcy).
        io_DestCols     width of the printout in printer pixels.
        io_DestRows     height of the printout in printer pixels.
        io_Special      flag bits
        io_TagList      a list of tags to specify more parameters for the
                        dump.

   TAGS
        DRPA_SourceHook a pointer to struct hook which is called to read
                        the source data. io_RastPort and io_ColorMap are
                        ignored and should be NULL.

                        The hook is called with object == NULL and message
                        is a pointer to struct drpsourcemsg. it must read
                        an array of source data.

                        Each pixel of the array is an ULONG of form
                        0x00RRGGBB.

                        Some printer drivers have set PPCB_NOSTRIPE which
                        means they cannot print in stripes. Using
                        DRPA_SourceHook is the best way for printing for such
                        printers because you can still prepare the printer
                        source data in stripes then.

                        The Source hook is always called in the context of
                        the printer driver DOS process.

        DRPA_AspectX    the X aspect ratio.
        DRPA_AspectY    the Y aspect ratio. This values overwrites the
                        aspect ratio from gfxbase or io_modes and is used
                        for scaling.