From: shd AT earthling DOT net (Steven Don)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Inline assembly question
Date: 15 Dec 1997 14:37:41 GMT
Organization: EuroNet Internet
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Message-ID: <673fbl$euo@news.euro.net>
References: <01bd0717$ffc6c1e0$3ca1f482 AT default> <882164794 DOT 925368334 AT dejanews DOT com> <34950998 DOT 37ED AT rug DOT ac DOT be>
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To: djgpp AT delorie DOT com
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In article <34950998 DOT 37ED AT rug DOT ac DOT be>, Vik Heyndrickx <Vik DOT Heyndrickx AT rug DOT ac DOT be> wrote:
>> >[snip]
>> > It this way of plotting a pixel the same as the farpokeb (...) version??
>> 
>> Using __djgpp_nearptr_enable should be a bit faster because you avoid
>> loading the ES register. But  !..., It may not work from a DPMI server to
>> an other.
>
>If you use the 'no selector' versions of the _far* function you don't
>have this load. 
>BTW this load takes more cycles than you may think because loading a
>selector register involves loading a descriptor, checking access rights,
>....
>
>One advantage by using the near pointer versions is that the compiler
>generates the code and that maybe further optimizations can be
>performed. But do not expect too much from that. IMHO it is not worth it
>using the near pointer functions. Now that I think of this, these
>optimizations may even break your code, since accessing video memory is
>always tricker than accessing 'normal' RAM. If the compiler manages to
>combine two consecutive by writes into a single double-byte write, your
>code may not work anymore. I do not know whether the gnu compiler is
>intelligent enough at this time to do this, but I wouldn't be surprised
>and eventually this optimization strategy may get in, and your code that
>once ran perfectly won't run anymore after recompilation.
*** And what about writing the pixel to an off-screen buffer and then blitting 
the whole frame when finished. You could just use an array and there's no need 
to fuss with pointers. I use this technique in my 3D engine and have no 
trouble with drawing 100000 poly's a second (including sorting, shading and 
scan conversion, of course). I like to think that's reasonably fast...

Regards,
  Steven Don