From: mvparvia AT alpha DOT hut DOT fi (Mikko V.I. Parviainen)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Allegro and blitting to screen
Date: 20 Jul 98 05:12:29 GMT
Organization: Helsinki University of Technology, CS lab
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Distribution: world
Message-ID: <mvparvia.900911549@snakemail.hut.fi>
References: <6onnuh$12p$2 AT oravannahka DOT Helsinki DOT FI> <MPG DOT 101ad9bbc1569c84989988 AT news DOT virgin DOT net> <mvparvia DOT 900873261 AT snakemail DOT hut DOT fi> <MPG DOT 101c82922011ae85989999 AT news DOT virgin DOT net>
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To: djgpp AT delorie DOT com
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a DOT gillett AT virgin DOT net (Andrew R. Gillett) writes:

>In comp.os.msdos.djgpp, article <mvparvia DOT 900873261 AT snakemail DOT hut DOT fi>, 
>Mikko V.I. Parviainen (mvparvia AT kvartsi DOT hut DOT fi) wrote:
>> a DOT gillett AT virgin DOT net (Andrew R. Gillett) writes:
>> >I've never understood the point of double-buffering. Are there any 
>> >advantages over page flipping?
>> Some time ago I made some tests in 640*480*256 mode. I have an P100
>> machine, with some very bad SVGA card. 
>> My test program used the whole screen. First, I tried page flipping.
>> It was annoyingly slow, so I decided to try double buffering, 
>> because it was very quick to code. The speed gain was unbelievable.
>> The blit was about two times as quick as with double buffering.
>> I think that the cause of this effect was the slowness of
>> video memory, but I am not sure. 

>I can't see how double-buffering could be faster than page flipping. Were 
>you using vsync() in the double-buffering version? If not, that's why it 
>ran faster.

Actually, the only function I changed betweeen these versions was
page_flip(), which in the page flipping version flipped video memory
pages and in the double buffering version copied the buffer to screen.
It has been awhile, but iirc there was a vsync in both versions.

I was very cnfused by the result myself. Perhaps I should check the
sources again.  
-- 
--
Mikko Parviainen
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