Path: utzoo!attcan!uunet!husc6!mailrus!uwmcsd1!ig!agate!twinkies!lippin
From: lippin@twinkies.berkeley.edu (The Apathist)
Newsgroups: comp.sys.mac.programmer
Subject: Re: flicker-free drawing
Message-ID: <12549@agate.BERKELEY.EDU>
Date: 26 Jul 88 01:47:00 GMT
References: <5727@orstcs.CS.ORST.EDU>
Sender: usenet@agate.BERKELEY.EDU
Reply-To: lippin@math.berkeley.edu
Organization: Authorized Service, Incorporated
Lines: 45

Recently jasmerb@orstcs.CS.ORST.EDU (Bryce Jasmer) said:
>I am writing a DA that needs to have flicker free drawing so I found
>and decided to use Scott Knaster's trick of letting the Tickcount change
>before drawing. Here is the code:
>-----
>aLong:=tickcount;
>while aLong = tickcount do
>	;
>EraseRect( {about 50 x 10 pixels} );
>DrawString( {about 10-12 characters (9 point)} );
>-----
>It works great while the small window is at the bottom of my screen but
>flickers more and more the closer you move the window to the top of the
>screen.

A better way to avoid flicker is to skip the erasing that causes it,
like this:

TextMode(srcCopy);
DrawString(whatever);
EraseRgn(area outside the string);

If you're replacing old text, you can do an EraseRect, using a
procedure like this:

void clearto(endofline)
  int endofline;
  {
   FontInfo info;
   Rect r;
   Point pen;
   GetFontInfo(&info);
   GetPen(&pen);
   SetRect(&r,pen.h,pen.v-info.ascent,endofline,pen.v+info.descent);
   EraseRect(&r);
  }

The only hitch is that srcCopy for text doesn't exist for the most
ancient hardware/system software combinations.

					--Tom Lippincott
					..ucbvax!bosco!lippin

	"It's a multi-purpose shape: a box."
					--David Byrne