Message-ID: <3411758B.AF94207@ecr.net>
Date: Sat, 06 Sep 1997 11:23:56 -0400
From: Jesse Legg <snowcrash AT ecr DOT net>
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Newsgroups: comp.os.msdos.djgpp
Subject: Djgpp inline asm/graphics (hline) question
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To: djgpp AT delorie DOT com
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Hello all! I am attempting to teach myself protected mode asm with djgpp
and have
been running into things that I could use help with. This group has been
very helpfully
in the past so I thought I'd pick your brains again! :)

I figured the best way to learn this stuff is to jump right in and start
doin' it. I am writing
graphics routines based off of some old pascal tutorials designed for
real mode but I
have managed to get a really cool (and fast) putpixel routine to work.
Now I'm writing
a routine for horizontal lines. It works (doesn't crash) but when
outputing to the screen
I get a broken line (every other pixel is off in a - - - formation). The
line is also drawn
one pixel early, like if you want a line drawn from (10, 23) to (200,
23) it sets the first
pixel at 9 instead of 10. I believe that I am not checking for an even
numbered pixel
correctly or there is something wrong with my jump operation (i'm not
that good at
jumping yet =) Also, what are the 'adc' and 'shr' instructions? (do they
even exist in
32-bit mode?). Any info/help is greatly appreciated! I copied the
relevant portions of
my code to the end of this message and will comment it on what i'm
trying to do...
I got a little sloppy :(

void H_Line_Fast(int x1, int x2, int y, unsigned char color)
{ __asm__ __volatile__ ("
   movw %0, %%es        ; loads es with _dos_ds
   addl %1, %%edi        ; put first x1 coord into edi
   movl %3, %%ebx      ; put y coord into ebx
   shll $2, %%ebx          ; multiply ebx by two
   addl %%ds:_screen_y(%%ebx), %%edi    ; add the pre-calc'd Y-value to
X coord

   movl %2, %%ecx        ; load ecx with second x2 coord
   movb %%al, %%es:(%%edi)    ; move the color, i originally had this at
the very end after stosb
   subl %1, %%ecx    ; subtract the x values, I'm gonna check this....
   incl %%ecx            ; increment counter

   testl $1, %%edi    ; test for odd number address (help!?? :)
   loopz Even            ; jump to even if on even address (?)
   stosb
   decl %%ecx          ; decrement the counter
Even:
   shr $1, %%ecx      ; from my real mode tutorial; what is this? :)
   rep
   stosw
   adc $0, %%ecx    ; ditto
   rep
   stosb
    ;orginally movb'd the color here..."
   : /* no output */
   : "g" (_dos_ds), "g" (x1), "g" (x2), "g" (y),
     "a" (color), "D" (0xA0000)
   : "eax", "ebx", "ecx", "edi"); }

I call the function like this:
   H_Line_Fast(10, 200, 23, 11);
and I know the y-coords are pre calculated correctly because it works
for my setpixel

BIG Thanks to anyone who helps me with this, I know it's kinda nasty! =)

--
 // Jesse