🚀 go-pugleaf

>    Does anyone out there know how to make QuickDraw work with the
> alternate screen buffer,i.e. is there a global that specifies the
> starting address of screen memory? I want to do some smooth animation
> and know how to cause the display hardware to switch between the
> two different screens. I just have to get QuickDraw to work with
> alternate screen buffer.
> 
> thanks
>  Tharakesh Siddalingaiah ---
>       University of Maryland Computer Vision Lab,     (301) 454-4526
>      ARPA:tk@cvl   CSNET:tk@cvl   UUCP:{seismo,allegra,brl-bmd}!umcp-cs!cvl!tk

     I don't think there is a global that tells you the address.  Once you
tell the segment loader which screen to use, you can get that information
from quickdraw, so you won't have to have $72700 in your program as a
constant.
     The way to get access to the alternate screen buffer is to tell the
segment loader that you intend to use it.  You have to use either Launch
or Chain.  There's apparently no way to have it happen from the finder.
Probably you should write a small dummy application that launches your real
application with the proper launch or chain command.  See the segment loader
part of Inside Mac for more info.
     Then your program has to tell the video hardware when to switch between
the two buffers.  To do this, set or clear bit 6 of address $EFFFFE.  Set
to 1 means use the default screen.  Clear means use the alternate.  To do
this in a nice sort of manner, $EFFFFE comes from the base address of the
VIA (found in the global "VIA" which turns out to be address $1D4 and it
usually contains $EFE1FE) plus an offset 1E00.  I don't think there's anything
in Inside Mac to explain this.

Brian H. Powell		brian@ut-sally