page flipping in vga mode 13h
Erwin Voogt
Can somebody give me some hints about how to perform page-flipping
with vga mode 13h (or with tweaked modes with a complete pixel in
each bitplane)? I've Richard Ferraro's "Programmers guide", but can
not figure how it should work.
Thanks, Erwin Voogt vo...@chem.ruu.nl
Clay Hellman
>Hi there!
>Can somebody give me some hints about how to perform page-flipping
>with vga mode 13h (or with tweaked modes with a complete pixel in
>each bitplane)? I've Richard Ferraro's "Programmers guide", but can
>not figure how it should work.
A very common method is to just simply zap the contents of a 64000
byte backbuffer to your VGA memory at segment A000, using a rep
instruction, tight loop (faster than rep on a 486+) or using DMA.
This is done right at the vertical retrace time to avoid flicker. On
today's PCs, this doesn't waste too much time since processors & V-RAM
& the whole shebang are so fast.
This is the ONLY way you can do it in straight Mode 13h due to a 64k
limitation in V-RAM, however if you unchain it, that opens up 256k of
V-RAM and allows you to flip your video buffer pointer between two
frames within V-RAM.
L8r
Clay.