Date: Fri, 16 Oct 92 16:30:23 CDT
From: csaba AT vuse DOT vanderbilt DOT edu (Csaba A. Biegl)
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: Re: Page Flipping under GRX? (sorry for the late answer)


> Tom Boutell writes:
> Has anyone attempted to accomplish page flipping under libgrx?
> Csaba Biegl's library is wonderful, and I know this probably isn't part of
> its original conceived intent, but while blitting GrContexts from
> memory can give the same effect (frame buffering), it's, well,
> not nearly as quick as a hardware page flip. I suspect that in
> lower - resolution modes, it should be possible. Any comments,
> particularly from Csaba himself of course? 

The next release of GRX will contain this feature. Until then a suggestion:

In my experience the fastest way to transfer pixels on a VGA is to use
a 16 color mode (this assumes, of course, that your application can
live with 16 colors) and use an aligned (SourceX % 8 == DestX % 8 == 0)
blit. This is a very fast way to transfer pixels IF the card supports split
Read/Write pages. If you use a 16 color mode which uses less than half 
of the video RAM, you can set up a second context in the invisible part
of the video RAM, and blit to the visible part every time the image must
be updated. This may be much faster than blitting from system RAM.


Csaba Biegl
csaba AT vuse DOT vanderbilt DOT edu