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*                                                                             *
*   Demo:   The Flag Demo      Type:    Amstrad CPC Emulator DSK File         *
*   Author: Odiesoft           Webpage: http://www.odiesoft.de                *
*   Size:   1 * 194816 Bytes   Date:    2. March 2003                         *
*   File:   Odiesoft Demos - The Flag Demo (1992).dsk                         *
*                                                                             *
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Title: The Flag Demo
Year:  1992


Well the story for this demo goes as usual: I saw a similar effect on the Amiga
of my brother and I've dragged my brain to figure out a way to convert the
filled polygon flag from Amiga to the CPC.

First I tried to create the flag as a vector graphics just with lines (and not
with filled squares). This, unfortunately, was too slow - the line vector
graphics of the flag still exitsts though.

Then I tried the whole thing with sprites, but this also wasn't good enough - it
was way to slow to paint 360 flag elements over and over again. So I came up
with the idea to use scrolling, so that I had just to paint the rightmost column
of squares and erase the leftmost column.

I used the CRTC register 3 scrolling trick to simulate a byte by byte scrolling.
(The CRTC is just able to scroll two bytes at a time, but by moving the whole
screen one byte to the left or to the right every frame and scrolling the screen
just every other frame you can simulate a byte by byte scrolling). I didn't know
that this trick often causes the whole image to flicker on some CRTCs and on
green screen. On my CPC 6128 with CRTC 0 it went okay...

Still, painting 12 elements at a time and removing another 12 on the other side
took up too much time for a 50 frames per second display. But I didn't use
direct addressing sprites in the demo, since I didn't knew about this method
when I wrote the demo. I believe that with direct addressing the flag maybe
would have been able to run with full 50 Hz.

Anyway, I believe that my approach to this problem was correct and resulted in
an unusual effect for a CPC demo. When I first presented this demo on the
Euromeeting II in Reims/ France in June 1992 most people were pretty impressed
and asked me how I did it, because some of them couldn't figure it out by
themselves...

The demo got finally released as part of the Castle Meeting Demo later that
year.

The sound in the Demo was compiled by DSC of Beng, but after the demo was
released it was the cause for a discussion between DSC and Kangaroo on the
copyright of the sounds, because Kangaroo claimed that he wrote the music and
DSC told me he did it. I don't fully recall how this discussion ended, but I
believe that DSC had to admit, that he just used his Soundtrakker to compile the
sounds into runnable files for my demo...

By the way you can switch between three different tunes by pressing 1 to 3
during the demo.


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*                                                                             *
* This program can be distributed freely and without the need of a written    *
* of a written permission by Odiesoft, as long as it is distributed free of   *
* charge!                                                                     *
*                                                                             *
* If you had to pay for this, you've been ripped off!                         *
*                                                                             *
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