From:	"Tony O'Bryan" <aho450s AT nic DOT smsu DOT edu>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Scrolling+sprites
Date:	Wed, 19 Nov 1997 13:16:26 -0600
Organization:	Southwest Missouri State University
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Ville Lundberg wrote:
> around it. But when I do this, by mixing double buffering and Allegros
> scroll_screen, the sprites flicker; they create "ghost" images, when
> running across the scrolling screen. It'looks terrible. My game uses

I imagine that what you're doing isn't quite what you think you're
doing.  Without seeing the actual code, here are some possibilities:

	1) When you copy your background to your working buffer, you're using a
copy mode that masks color 0.  This means that pixels from the previous
screen that are under any occurance of color zero aren't erased.  This
will result in "bleed-through" images (partial images from the previous
frame).
	2) You're updating the wrong frame buffer.  You may intend to update
the invisible working screen, but you're actually updating the currently
visible screen.  This will result in flicker and massive "ghosting"
since the visible screen gets updated on the wrong frame.
	3) You're not accurately tracking your invisible and visible screens. 
This causes very unpredictable results depending on how mangled your
buffer-tracking routine is.

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