From: brennan AT news DOT rt66 DOT com (Brennan "The Rev. Bas" Underwood)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: fast vbe graphics
Date: 7 Apr 1997 16:54:53 -0600
Organization: Acid Brain
Lines: 48
Distribution: world
Message-ID: <5ibtvt$3f4$1@mack.rt66.com>
References: <01IHEKLS7NOI92SA7U AT NICKEL DOT LAURENTIAN DOT CA>
NNTP-Posting-Host: mack.rt66.com
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

In article <01IHEKLS7NOI92SA7U AT NICKEL DOT LAURENTIAN DOT CA>,
 <S2200253 AT NICKEL DOT LAURENTIAN DOT CA> wrote:
>I'm trying to get fast vbe 2.0 (with linear frame buffer) graphics
>at 640x480x256 yet am having some difficulties.
>
>I'm drawing the images to a video  buffer (video[640*480]) and then
>try to display with
>
>for(int i=0; i < 307200; i+=4)
>{
>        temp = ((unsigned long)(video[i])) << 24\
>        + ((unsigned long) (video[i+1])) << 16\
>        + ((unsigned long) (video[i+2])) << 8\
>        + ((unsigned long) (video[i+3]));  
>        
>        _farnspokel(i, temp);
>    
>}

You're going to a lot of trouble to build a dword from chars. You could
rewrite the loop, casting video to be an int *, or you could drop to
assembler like so:

/* displays 307200 bytes from video into the memory pointed at by selector,
starting at byte 0 of the segment */
void display_it(int selector, void *video) {
asm (
"pushw %%es\n\t"    /* save es from @destruction */
"movw %0, %%es\n\t" /* load user selector into %es */
"cld\n\t"           /* want to copy forwards */
"rep\n\t"
"movsl\n\t"         /* copy from ds:esi to es:edi ecx times */
"popw %%es"         /* restore es */
: /* no output */
: "g" (selector) "c" (307200/4), "S" (video), "D" (0)
: "%ecx", "%esi", "%edi" );
}

Unfortunately, I'm not in a situation where I can test this, as NT keeps
aborting gcc for some reason. I've used code like this before, though,
and I'm sure I'll find out very quickly if that's broken.


Brennan
-- 
 brennan AT rt66 DOT com |  Ding-a-ding-dang my dang-a-long-ling-long.
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   Rasterfarian   |  <http://brennan.home.ml.org>                          -O