From: Shawn Hargreaves To: djgpp AT delorie DOT com MMDF-Warning: Parse error in original version of preceding line at relay-11.mail.demon.net Subject: Re: Changing the color palette Date: Fri, 25 Apr 1997 11:13:11 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Message-ID: <861971208.09281.0@[194.129.18.166]> Precedence: bulk Roger Noss writes: > From http://www.execulink.com/~pweeks/chapter.html, I read that you can > change a color in the palette by writing to 0x3c8 and 0x3c9. I tried it and > it works. > > Does anyone know when the palette is changed: instantaneously or on the next > vertical retrace? Instantaneously. But it's not a good idea to change it at any times other than the retrace, because: a) When doing fades, this can produce nasty phase effects as bands of slightly different colors move up or down the screen. b) Most cards can't read and write the palette registers at the same time. This means that whenever you modify them, there is a moment when the display circuitry is unable to access them, so it outputs a few pixels of garbage to the screen. This is described as "snow", and doesn't look very good! It's much better to wait for a vertical retrace before you modify the palette: take a look at Denthor's VGA tutorials in the PCGPE for more information about this (ftp://x2ftp.oulu.fi/pub/msdos/programming/gpe/). -- Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk "Beauty is a French phonetic corruption of a short cloth neck ornament"