NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/comp/windows/x/i386unix/137

Internet Message Format | 1992-12-23 | 1.6 KB

Path: sparky!uunet!olivea!charnel!sifon!thunder.mcrcim.mcgill.edu!mouse
From: [e-mail] (der Mouse)
Newsgroups: comp.windows.x.i386unix
Subject: Re: 32K or 16M colours?
Message-ID: <[e-mail]>
Date: 23 Dec 92 17:19:33 GMT
References: <linda.724803368@minnie> <[e-mail]> <[e-mail]>
Organization: McGill Research Centre for Intelligent Machines
Lines: 22

In article <[e-mail]>, [e-mail] (Thomas Roell) writes:
>> Take a look at how the 24-bit SVGA's are implemented.  Packed 3-byte
>> pixels.  It's going to make working on them rediculous[sic].
> I don't think 3byte pixels is that rediculus[sic] if you look at the
> memory contraints given in todays SVGAs.  But the price to pay is
> VERY high.  You can only deal with 24bpp (opposed to 32bpp) by using
> 32bit reads/writes.  A simple statistic shows that about every second
> access will be not correctly aligned and hence at least 2 32bit
> accesses to video memroy will be necessary.  Having this in mind a
> 24bpp framebuffer will be at leat 1.5 times slower than a 32bpp.

Only if the implementation is careless.  You should be doing three
32-bit memory accesses for every four pixels.  Only if you're doing
something narrow (ie, small span along the x axis) will the
misalignment effect make much difference.  Granted, drawing lines is a
common operation, but I believe area copies and text drawing are much
more important for nearly all applications.

                    der Mouse

                [e-mail]