Timeless

Quick Port of the TimeLess project , first of all there is no sound in it yet so
don't whine about that missing.

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Keyboard controls:
escape     = exit
f          = fast forward
space      = pause
1          = flip to showing the offscreen 256x256 bitmap


This package is released under the GPL.


CHANGE HISTORY + BACKGROUND:
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Fri Jan 27 08:07:49 PST 2006
David Ashley (dash()xdr.com)

Version 1.00

This is a port to linux/SDL of Tran's (aka Thomas Pytel) Timeless demo of
1994. The demo was written in 100% assembly code and so wasn't portable.
I spent a lot of time looking at the demo in those days, and showing it
to other people (so I must have liked it). It is worth keeping around, I
think. It was an MSDOS program with its own dos extender, which lets you use
32 bit instructions + addressing modes.

There were various complications in doing the port. The code was designed
for VGA mode-x which separates every 4th pixel in the video memory into
a separate region of memory. This lets you get access to more than the 64K
video memory window alotment and you can do page flipping. However it's a
headache to program. And it made the task harder because this code has to
be unravelled. Under SDL we're just a flat 320x200 frame buffer.

There are 3 layers to the demo. Layer 0 is the background. In the original
source this is done using a 32000 word table that tells you how to move
in an offscreen 256x256 byte buffer. The movement in the buffer wraps around
in both x and y. Onscreen you're seeing a warped display of that buffer,
and that's the most interesting visual affect of the demo.

I didn't want to have too much data in this source, so I wrote code to
generate a buffer similiar to the one in Tran's source. It uses sines and
cosines and I tried to come up with a model for Tran's choice of the radius.
I think the intent was a 3D projection, however I don't really know what
his choice of R values were based on. This probably makes no sense whatsoever
but I can't be bothered to explain. Suffice it to say my algorithmically
generated warping table is almost exactly like Tran's, however with mine
you can see how it's generated in the source. His algorithm must have been
quite similiar.

The 1st layer is drawn into by all the r_pXX functions. I've implemented
these all.

The 2nd layer is the sprites that move around the screen. These just add some
spice to the demo. These sprites were implemented in the original source
as data statements. It turns out the data statements represent X86 machine
language code to bang the right byte values to draw the sprites onto the
buffer at the address pointed to by edi. I wrote the gensprites.c program to
decompile these programs and output pixel data, which becomes the sprites.c
file. All the 2nd layer sprite hacks are implemented in this version of
the source. These are the r_l1pXX functions.

The 3rd layer is on top of the sprite layer, and I haven't implemented any
of these functions. This layer shows a circle and the circle is meant to
represent a sort of window into something else. In one instance the window
is a view into the offscreen 256x256 bitmap -- sort of the magician showing
how the trick works. This is a very nice touch by Tran, in my opinion. Another
window just shows a representation of the entire screen, shrunk down so it
fits into the circle. You can even see the circle itself in the circle as I
recall.

Meanwhile while these 3 layers are going on, there are palette effects going
on, the colors are changing in interesting ways, fading in and out, etc.
The layer0 background is also getting shifted around, the scanning point is
moving around, the angle offet, and the scanning table itself is getting
warped. It all adds up for a lot of variety.

My original intent with this port was to make a cross platform version that
would pass down through the ages, and be identical to the original version
in every way. That means at exactly the same frame you'd see the same
sprites moving around, the 256x256 bitmap would contain the same data,
the music would sound the same -- in short it would be a faithful
reproduction of the original.

However over the course it has gotten extremely tedious to study the code and
divine what was the original intent. It is very easy to make a mistake.
The code is real spaghetti, difficult to read. It may be fast but it's not
very intuitive. I have given up on even implementing the sound for now. This
is unfortunate, because the music that plays during the demo is a big part of
the demo. It's kind of haunting.

You can run the original timeless.exe under dosemu. It runs slower than hell,
but you can run it. I got some things to appear right. But the background
doesn't match at the right place + the right time. My background gives
the same "effect" as the original, however it's not frame by frame identical.
I discovered there are some timing dependencies on how the palettes are
faded from one to another, and my version doesn't match the original. I was
trying to study the original to figure out the original code's intent when
it just hit me...I don't have time to get it absolutely perfect. I just sort
of gave up. My version is close enough to the original to reflect the essence
of Tran's intent, in my opinion. If someone wants to make it absolutely
identical, well the source is right there and you can figure it out.

I can confirm:
1) All the sprite image data is identical to the original
2) All the background 32x32 bitmap data is identical to the original
3) All the palette data is identical
4) The random locations of the fishies appear to be identical. Perhaps
other l1 sprite code is identical. I think the snow was identical, I
saw similiar patterns between the two.
5) My handling of palettes is not exact, and so the timings are off.
This could affect everything. There is some machinery in there to fade
the palette at 1 unit per iteration, or 2 units per iteration. It looked
like the decision of which speed to use is based on how many colors are
to be faded. That's when I gave up, it seemed ridiculous.
6) I think my gnbg routine is correct, but if the scanning of the
starting point in the 256x256 offscreen buffer doesn't match that would
make the appearance not match.

Anyway Tran says it took him 1 to 3 weeks to write the demo. I've probably
invested about a week or so in this port. I can't see putting more time in
the port than it took to make the original -- just to make the port
*exactly* like the original.

So I'm calling it quits. If this is useful to anyone that's great. I'd
like to see it rolled into an xscreensaver hack, that would be cool.