wrote:
http://users.aol.com/DGoncz/Publications/Modes.gif
will show to you that many common video modes require only padding by 2
to be scanned diagonally without retrace.
Any questions, anybody?
Mainly why, both on a practical basis (your method is complicated
and it's not obvious that it would present a better picture,
require less hardware, be amenable to rasterization, or allow
random video adapters to work with random monitors) and a
theoretical basis (your emphasis on greatest common div's).
Regarding gcd's, I don't see why a cell-based display would need
co-prime horizontal and vertical sizes. Correct me if I'm wrong!
Also, your program's "while" loop means that your Modes.gif does
*not* show anything about padding by 2, since it may have padded
by 4, 6, ... as well. You are right, but the program doesn't
show it. Here is some program output that does:
H V .. +. ++ .+ -+ -. -+ .- -- #. ## .# =# =. =# .= ==
640 480 160 1 1 1 1 3 1 1 1 6 2 2 2 2 2 2 2
800 600 200 3 1 1 1 1 1 1 1 2 2 2 14 6 14 2 2
1024 768 256 1 1 1 1 3 1 1 1 6 2 2 14 2 14 2 2
1152 864 288 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2
1280 960 320 3 1 1 1 1 1 1 1 2 2 2 2 6 2 2 2
1280 1024 256 1 1 5 1 1 1 1 1 2 2 2 18 2 18 2 2
1400 1050 350 3 1 1 1 1 1 1 1 2 2 4 2 6 2 8 2
1600 1200 400 1 1 1 1 3 1 1 1 6 2 2 2 2 2 2 2
1800 1440 360 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2
This is from http://pat7.com/jp/omni-di.c . In the headings,
.. means +0, + +1, - -1, # +2, = -2, for H or V in left/right
place. Eg: the .. column is value of gcd(h, v) [or, v/3 if
aspect ratio is 4:3] and the =# column is value of gcd(h-2, v+2).
As Don Nichols points out, there are a lot of different display
resolutions in use. Some VESA sizes [see items 35 and 36 in
http://en.wikipedia.org/wiki/Extende...ification_data
] a
720x400@70 Hz, 720x400@88 Hz, 640x480@60 Hz, 640x480@67 Hz,
640x480@72 Hz, 640x480@75 Hz, 800x600@56 Hz, 800x600@60 Hz
800x600@72 Hz, 800x600@75 Hz, 832x624@75 Hz, 1024x768@87 Hz
1024x768@60 Hz, 1024x768@70 Hz, 1024x768@75 Hz, 1280x1024@75 Hz
but VESA sizes aren't the whole story, because many people like
to set up custom modelines in their X Windows System config files.
It might be worthwhile for you to google Modeline and/or read
man XF86Config. Note that besides H and V display limits,
modelines also specify hsyncstart, hsyncend, vsyncstart, and
vsyncend.
-jiw