Message-ID:	<33F8B04B.AEC7D9AF@ecr.net>
Date:	Mon, 18 Aug 1997 16:27:56 -0400
From:	Jesse Legg <snowcrash AT ecr DOT net>
MIME-Version:	1.0
Newsgroups:	comp.os.msdos.djgpp
Subject:	inline asm putpixel routine using table
NNTP-Posting-Host:	207.40.127.216
Lines:	54
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

    Hi, I've been working with writing my own graphics routines in DJGPP

using mostly inline asm. My only references are a couple of (old) Pascal

files and some non-protected mode assembler texts as well as various
DJGPP graphics programming docs which give slow examples for my
taste! I have converted several putpixel routines to inline assembly but
in
effort to get even faster =) I am attempting to pre-calc 320*y into an
array (globally defined,  btw) to eliminate the multiplication step...
here is
my function:

void _setpixel(int x, int y, char col) {
 __asm__ __volatile__ ("
   movw %3, %%es
   addl %0, %%edi
   movl %1, %%ebx
   addl %%ebx, %%ebx
   addl %%ds:_screen_y(%%ebx), %%edi
   movb %%al, %%es:(%%edi)"
   : /* no outputs */
   : "g" (x), "g" (y), "a" (col), "g" (_dos_ds), "D" (0xA0000)
   : "eax", "ebx", "edi");  }

Now the part that is baffling me... this works when you set a pixel with

and EVEN numbered Y coordinate but it only plots the X-coordinate
accurately (ie. Y is in the wrong place). When you attempt to set a
pixel
with an odd numbered Y-coordinate it crashes(!?). I am new to assembly
and have been able to figure out several other problems I've had but
this
seems crazy (though i'm sure obvious to you pros)! =)
Can someone please explain this for me?? (i'm dying to understand!!)

Also, I initialize the 'int screen_y[199]' array like this:
void calc_screen_y(int width)
{
 int i;
 for (i =0; i < 200; i++)
     screen_y[i] = i*width;
}
I'm working in mode 13h and call calc_screen_y(320); right after
initializing the video card (at the begining of the program).

Anyone who can help, MUCH THANKS in advance! :)

--
_/_jesse___________________________________________________
 "The Adventures of Batman and Robin is rated TV-Y7
   because it is a Super Heroe Action Drama."
    -- Fox Kid's show introduction

- Raw text -