DirectX VRAM-VRAM accelerated stretch blit

DirectX VRAM-VRAM accelerated stretch blit

Evert

Member #794

November 2000

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Evert, my entire post is one statement, i wasn't expecting to have individually sentences picked apart, reading the post backwards takes it out of context.

I thought I'd structure my reply in such a way that I could individually comment on the things I have questions about. I also thought that I'd just put the quick question in front, before the one where I would put a bit more discussion or clarification to what I was saying. But if you prefer it the other way around (and you might bother answering the question this time):

Allegro uses self-modifying code to stretch sprites on Intel machines (more accurately put, it assembles a piece of code in memory to do the stretching and then calls it). I can imagine that that can still be an efficient way of doing it on modern machines (even if the code generated is i386 oriented). And what do you mean be `luck making a stretch_blit in C'? Allegro already has one; have you looked at that?

By the way, as this has nothing to do with the original topic (VRAM->VRAM accelerated stretch blits), I'd prefer the discussion be moved to its own thread to make it easier to track.

A J

Member #3,025

December 2002

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what do you mean be `luck making a stretch_blit in C'?

I mean, has anyone made a stretch_blit in C, not asm, that can compile on all the supported compilers, and is as fast or faster than the current asm stretch_blit code ?

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Allegro already has one; have you looked at that?

It has? where?
Im confused, as when i asked "As for the asm code in allegro, which routines need re-writing?" i didn't get a specific answer, but i did get a hint "Only 32 bit Intel ports use ASM code"

Getting a straight answer seems to be really difficult, so all i can do is ask lots of questions; and pick apart a few answers to try to establish what is going on, and at the moment, it seems that there is consensus about droping the asm code ASAP, in favour of C equivalents. I can't establish the current state of that work, for direct and specific questions like "As for the asm code in allegro, which routines need re-writing?", the answer i got was "all of them".

As i have already written a fast SSE2 blit, and we all seem to be in agreement about memcpy() being a suffecient blit replacement; i thought i might try asking about the status of stretch_blit and wether anyone had written a C equivalant of it.

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and you might bother answering the question this time

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.. obviously someone has had some luck...

i'll obviously answer when i could be bothered

___________________________
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Fiddler

Member #5,385

January 2005

A J, Evert is trying to say that Allegro already has a C version of stretch_blit, which is used in all platforms except for the x86 CPUs. You can use that as a base trying to develop a possibly faster version.

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Evert

Member #794

November 2000

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It has? where?

allegro/src/c/cstretch.c

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Im confused, as when i asked "As for the asm code in allegro, which routines need re-writing?" i didn't get a specific answer, but i did get a hint "Only 32 bit Intel ports use ASM code"

Well, what are you asking? What routines need to be rewritten in C because there's only an ASM version of the code? or If I want to make more efficient ASM code routines, which routines should I rewrite?
The answer to the first question is none, or else Allegro would not work at all on non-i386 machines. The answer to the second question is probably `all of them'.

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it seems that there is consensus about droping the asm code ASAP, in favour of C equivalents.

Yes. The main reason being, if and when things are changed in the API, we don't want to simultaneously be developing an ASM and a C version of the code. We need the C version anyway, so let's stick with that, at least for now.

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As i have already written a fast SSE2 blit,

Did you submit a patch for that?

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i thought i might try asking about the status of stretch_blit and wether anyone had written a C equivalant of it.

Yes, of course someone has - or Allegro would not work on non-i386 machines.
Now if you can optimise it more than it is now, that would be great. Personally, I can't even test it against the ASM code, so I have no idea how much slower it is (if at all).

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Quote:
and you might bother answering the question this time

Quote:
.. obviously someone has had some luck...

i'll obviously answer when i could be bothered

Well, I assumed you were aware that Allegro works on non-Intel machines (G4/G5 Mac's, say), so I assumed you were aware of the Allegro C-only port. If you weren't, fair enough. If you were, I still don't understand your question.