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Path: utzoo!watmath!clyde!rutgers!sri-spam!sri-unix!hplabs!sdcrdcf!trwrb!sansom
From: sansom@trwrb.UUCP
Newsgroups: comp.sys.atari.st
Subject: Re: double buffering using vdi ops
Message-ID: <1570@trwrb.UUCP>
Date: Thu, 29-Jan-87 22:37:07 EST
Article-I.D.: trwrb.1570
Posted: Thu Jan 29 22:37:07 1987
Date-Received: Sat, 31-Jan-87 07:21:19 EST
References: <2430@mtgzz.UUCP>
Reply-To: sansom@trwrb.UUCP (Richard Sansom)
Organization: TRW EDS, Redondo Beach, CA
Lines: 39
Keywords: Help needed

In article <2430@mtgzz.UUCP> bds@mtgzz.UUCP writes:
>How does one use the Setscreen() xbios routine to do double buffering
>with vdi operations. Is there a trick to this? When I set the
>logical base to an array and do vdi operations followed by setting the
>physical base to the array, the result is garbage. Any suggestions?

You must make sure that your buffer starts on a 0x100 byte byte boundry
or the display _will_ be garbage.  Try this:

char screenbuf[32256];		/* (160 x 200) + 256	    */
long screenptr;			/* address of new screen    */
.
.
.
/* get the new screen's address & make sure it's on a 0x100 boundry */
screenptr = (long)(0x100L + ((long)&screenbuf[0] & 0xffff00L));

/* make the new screen both the physical & logical screen */
Setscreen(screenptr, screenptr, -1);


That should do the trick (warning - this code is untested in that I've
generated it here at my terminal; still, if I've made no typos, it
should work).

-Rich






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