System Booster/System Booster.iso/Archives/HardwareProjects/PAL_on_SVGA.lha/PAL_on_SVGA

Text File | 1996-01-02 | 5.5 KB | 100 lines

2/01/96

Game coders! Please read the following, it is such a simple "discovery" that I
cannot believe no-one has thought of it before. It is about displaying 15kHz
pal screens on Standard PC SVGA monitors. Now before I explain what I have
found, I will give my relative hardware specs:

A1200, KTX-14" non-interlace Multiscan SVGA monitor <note: NOT a multisync. A
standard SVGA monitor, costing NZ$330, or about 140 UK pounds>. The adapter
to connect the SVGA to my A1200 is a copy of the old C= monitor adapter from a
1942 monitor. Virtually the same as the Amiga2VGA docs that can be found on the
Aminet.

Usage:
OK. How do I display PAL images on my SVGA? Incredibly easy! First step is to
DOUBLE the pixel width of the inteded mode you want. Eg: If you want to display
a 320x236 PAL mode, then choose 640x256. If you want 640x512, use 1280x512. Ok,
you CANT do Pal-SuperHires, but Im sure people are not going to complain too
much. The next step, and final step, is to completely IGNORE the left half of
the screen mode. EG: For a 320x256 PAL mode <WHICH MOST _GAMES_ ARE RUN IN>,
keep the left 256 pixels BLACK and utilise the RIGHT 246 pixels of the 640x256
PAL mode that would be needed to display the image on the SVGA monitor. And
_thats_ it! The picture comes up as a clear, colourful image. It even looks
like a 1942 displaying 15kHz PAL modes, as  every second line is "missing"
<Which is a feature of PAL - as it is only 15kHZ, it is half the bandwidth of
the higher, DBL-Pal mode and as SVGA/1942 monitors have a high DPI compared to
TV's, the 15kHz scanrates appear this way, but you cannot really tell on a TV>
Now, the picture is _Extremely_ Stable. The monitor is in its ~31kHz mode, or
what it would be in if DBL-PAL was being used. In one respect, it is better
than a 1932/1940 as you dont hear the high pictch 15kHz "squel" that TV's and
most 15kHZ monitors give out.

Technical:
OK, Im studying to be an Electrical engineer, but I cannot guarantee the
following is completely correct, but I am pretty sure its right.
The SVGA monitor is thrown in to its 31kHZ mode when the Amiga outputs PAL. Im
not sure if this will happen on all other SVGA monitors. but if you go into PAL
and you can make out a bit of the screen, and it looks wrapped around itself,
then your monitor should be able to do what I have explained above.
Because it is trying to display a 15kHz image on a 31kHz bandwidth, one line of
PAL 15kHz will be used "twice" by the 31kHz monitor, as the elec guns are
moving twice as fast. Its not a straight double, but more a "one and a half"
wrap around the screen. If you move into a pal screen, and move the pointer
from left to right across the screen, you will see the mouse move across the
SVGA screen quickly, and stretch back to the left <when the mouse is halfway
across the PAL screen> And then proceeds to move across the SVGA screen again.
So what you are infact doing when using the right hand side of the PAL screen,
so that the monitor only draws the right half of the pal image across the WHOLE
of the SVGA monitor.

Pictyre Quality:
The PAL picture is not exactly centered on my KTX SVGA monitor. Its slightly to
the right I think, but this is easily fixed by using the horizontal shift. You
can use the first half of the PAL screen to display images onthe SVGA, but I
think the quality is better, and it is less prone to have stretch marks where
the SVGA wraps around itsel. My monitor, for example, in PAL 640x256 <no
overscan> can use from pixels 313-=>639, which is 323 pixels wide, compared to
only 317 if the left side of the screen was used. Apart from that, you would be
hard pressed to tell the difference between the SVGA and a 1942.

Notes:
This may not work on ALL SVGA monitors. It may only work on mine. If you do
have a SVGA monitor, please email me and tell me how you got on, so I can
compile a list of monitors and Percentages on how many SVGA owners can do this.
I will then post these listings and encourage programmers to take advantage of
this simple idea.
The reason why I am excited about this "idea" is that in a lot of games, it is
hard/impossible to incorporate a screen mode requestor to choose the mode to
run in. Some games have them, like Gloom-Delux and Nemac4, bu 99% of commercial
games dont. Some games, like Extreme Racing <which is a brilliant game> cannot
be programmed to run in DBL-PAL. To get maximum speed from the machine, PAL
15kHZ needed to be used. So what option is there for us SVGA monitor owners???
GIVE THE GAME AN OPTION FOR SVGA IN WHICH IT IS RUN IN PAL-HIGHRES AND ONLY
UTILITSES THE RIGHT-SIDE OF THE SCREEN! This will be viewable on TV's and the
like, with the picture displayed ont he right-side of the screen, but also
beautifully on the SVGA monitor. Surely this isnt a hack, and would take only a
little coding.

Well people, what do you think? I think it is a viable option for game coders
to include in games, rather than using direct-mode promotion. Ok, I am not sure
if it would work on GFX cards or not, more likely not, but for the majority of
people who own SVGA monitors, it would work. And that, would make a lot of
people very happy, not at least me. <Imagine worms in this mode: Hell! You wold
be able to read what the worm's names are!>

Kenji Irie.

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