🚀 go-pugleaf

I don't know if this is appropriate for this group, but I am pretty
desperate, so here goes:

I am in the process of porting a piece of code from VGA Mode 13h (320 X
200, 256 colors) to VGA Mode 12h (640 X 480, 16 colors).  I have art
that has been algorithmically converted to 320 X 200, 16 colors then
touched up by hand.  I am expanding this art by doubling all of the
pixels on the fly when I load the images into memory from disk, and
leaving 40-pixel-tall blank strips at the top and bottom of the screen.
Hence my final image size is 640 X 400.

My problem is that my blit routine is slow.  I am presently using write
mode 0 (byte-at-a-time) and addressing each of the 4 bit planes
separately.  Since I am inexperienced with Mode 12h and EGA-format
graphics in general, I am wondering if I am missing something.  My
understanding is that in mode 12h I do not have access to page flipping.
Is this correct?  If so, does anyone out there have any suggestions for
fast algorithms for moving rectangular regions from main memory to the
screen in this mode?  BTW, as far as the registers go mode 12h behaves
the same as the old EGA mode 10h (640 X 350, 16 colors) for anyone who
has worked with 10h.

I am under rather severe deadline pressure, so prompt advice of any kind
would be greatly appreciated.  However I don't have any choice about
this -- as kludgy as it sounds (is) I *have* to do it, so please spare
the flames.

Please e-mail me as I do not regularly read this group.

Thanks!

M.