From:	Shawn Hargreaves <Shawn AT talula DOT demon DOT co DOT uk>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Allegro Vesa mode graphics
Date:	Thu, 6 Feb 1997 20:26:51 +0000
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Till Harbaum writes:
>> and also a protected mode interface that can be used for the standard
>
>Are there any examples how to access this interface? At the moment i

Look at the Allegro sources, in vesa.c. You will also want a copy of the
VBE 2.0 spec: this can be found on http://www.rt66.com/~brennan/djgpp/.

>copy my buffer in parts of 64k and use the int10 call to switch between
>the 5 windows i need. How much slows the usage of the int10 window
>switching the screen update down compared to a linear frame buffer
>or a windowed buffer with proteced mode window switching?

The int10 call is several thousand times slower than doing everything in
protected mode. But if you are just doing a ram->vidmem blit, and so
only using five bank switches, this difference is negligible. It is when
you are drawing to unsorted, non bank-coherent locations that it has a
big effect.

The linear framebuffer is well worth using even if you are just blitting
to the screen, though, because a lot of recent cards use different
memory interfaces for linear and banked access, and can accept data
faster in linear modes.

/*
 *  Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/
 *  Ghoti: 'gh' as in 'enough', 'o' as in 'women', and 'ti' as in 'nation'.
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