From: ao950 AT FreeNet DOT Carleton DOT CA (Paul Derbyshire)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Allegro question
Date: 7 Aug 1997 07:21:35 GMT
Organization: The National Capital FreeNet
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"Zoma" (Zoma AT sprynet DOT com) writes:
> I use Allegro, and think it is great, but there is a strange "error?" that
> occurs with its graphics routines.  I am using Mode 13h and whenever I
> clear the screen, a border forms around the edges of the screen in the 0
> color.  Why does this happen, and how can I prevent it from happening?  I
> don't use black as my zero color, so this is beginning to get annoying. 

I doubt it's Allegro. Monitor hardware does strange things sometimes. Many
monitors will display images of slightly different physical size (in
centimeters or whatever) in different modes. If the entire 320x200 pixels
in Mode13h is being drawn on an area smaller than the physical size of the
screen by the monitor hardware, then there will be some parts of the
screen and phosphor not lit up, at the edges: your black border. Some
monitors have adjustments for the width and height of the image and its
centering, but as far as I know these won't do that much good if the image
changes slightly in different modes.

My own monitor will use the whole phosphor area for 1024x768, won't
display 800x600 at all for some odd reason, leaves a large grey-black
border at 640x480, but no such border in 320x240, 320x200, or in some text
modes.
--
    .*.  Where feelings are concerned, answers are rarely simple [GeneDeWeese]
 -()  <  When I go to the theater, I always go straight to the "bag and mix"
    `*'  bulk candy section...because variety is the spice of life... [me]
Paul Derbyshire ao950 AT freenet DOT carleton DOT ca, http://chat.carleton.ca/~pderbysh