Tutorials - More colours!!! Description packer color video from the demo "Weed".

<b>Tutorials</b> - More colours!!! Description packer color video from the demo

More colours!!!

Poisoned Cyberjack / / TriebkraftNE

Trying to do something impressive for the 'weed', I haven't
expected such a good results. A lot of people asked me at the
party 'is it multicolour?'. Meanwhile, it is all that simple -
this is just packed fullscreen animation. Packed well,
indeed ...

Outrage of colour, seen at the screen, is not the result of
engine's work, but a correctly done original picture.
Gd / / tbk / / 4d is the one to answer how it could be done, he
rendered it in lightwave 7.5. After that I converted avi files,
using bmp2scr_1.75 by LCD. I worked only with the screens
received from such a conversion.

That's all I had to tell you:). But because of a good mood
I'll speak about the packer itself ...

The demo features 198 coloured screens, shown within a little
amount of time. This occupies 1.368.576 bytes in not packed
form. 290k in zip (hrust does nearly the same). Laser compact
packed it takes a little less space, but it still makes no
sense because of huge size. That's why original packer was used
to compress it all in 80k, i.e. Each screen is about 400 bytes
long!!! And who cares about quality loss:)

Diver / / 4d brought up this idea long time ago in 2001. Why not
combine hi-res and low-res, pixel graphics and attributes in
the engine itself, to obtain a lot of colour and high speed. I
didn't fulfil it in full scale, still, but it would be a lie to
say that I'm trying to do this from dusk till down.

And now, a bit of history ... Two years ago diver came with idea
to make a demo, absolutely unprecendental on speccy. To make
the hardware do its maximum without multicolour technique,
everything have to be done using perverse combinations of
low-res and hi-res, attrs and pixels. Don't forget, this is the
main powerful feature of speccy, otherwise it could lose the
other computers, released later and having better
specifications at start. Because of averagely high resolution
of coloured screen and very high speed of screen updating
(Maybe not so, but the size of screen data is small), western
authors released games till the middle of nineties, when
majority of the other home computers were almost dead. For now
this feature is practically out of use - either people are
working with pixels (vectors, dots, chunks 4x4), or with
attributes, but the same way as with chunks (8x8, various forms
of multicolour). The real combining is never used - it's too
hard to code and the purposes of use are far too specific.

But diver is a keen minded person;) he invented a lot of ideas
(More than a half of which is unrealisable as I see it;) we
doesn't succeed with that demo, being busy with other projects
(Harm demo, moorhuhn game), and because of diver's army
service ...

I didn't forget those ideas, but there was no time to shape it
out. And finally I came to it only this year, making up
detroYt. There was no effect in the middle, I had an idea, but
was pressed by the lack of time and there was no memory for
animation. Thinking for a while, I found my old chunk engine,
cut everything about real-time calcs, fixed bugs, redone it for
2 colours and got a part with a flying pinions as a result.
Just to mention - 230 screens occupied 22.5k.

Nearly this time in April I've got an idea to do a colour
animation. But confronted with difficulties - it was hard to
make detroYt's engine use colours, packing was bad and
decompression speed was below 5 frames (the threshold we set).
That's why I spit upon all this tortures with chunks depacking,
shit with c2p, and did everything as simple as it could be -
just compressed all screens. But, truly saying I used chunks,
therefore something left from the old method ...

An idea behind this mythical engine is simple, although its
perverse. We are building a screen in a chunk buffer (not
dealing with screen addressing problems or working with bits)
1x1 or 2x2 (I've chosen this variant as it is optimal by speed
and amount of stored data - chunks 2x2 roxx !!!). But it can't
be done as it is (don't ask me why - its clearly seen), that's
why I used some tweaking - processed the screen in two passes.
On the first we are counting only height's colours - 33x25
chars grid. For the massive coloured objects there would be a
lot (more than a half) chars, where all four heights have the
same colour. Such chars c2p fills with this colour and forgets
about it. The rest has to be detailed - we count edges of chars
(2 pixel step in my case), after that we find the needed chunk
(Or sprite if its easier to understand), and finally putting it
in a char cell on the screen. It's more complex with colour -
but I decided to use colours of first two heights and forget
about it ... This is the short explanation of an idea behind the
new wonderful coloured engine, that is not realised till today
:)))

There wasn't time, nor desire to complete it (laziness is the
main reason:) one thing I did till the end - drawn all chunks
(It could be generated, but 'handmade' is our main principle
:). The main problem is the second pass on the chunk screen -
its too abstruse: (((therefore there is no blasting real-time
in our last demos - just very cool crunching ...

How it was done in detroYt: at first, depacks the colour grid
for the char's heights, then, using the four heights of the
char, the type of the sprite is defined. We got 16 types of
sprites, two of it were not drown at all (black filled chars 
were instead of it:), and the next two are just chars filled 
with paper = ink. 12 types left, for everyone of them I have 
drawn 16 sprites by hand. Number o sprite (4 bits) is taken 
from the packed data. I'll not explain what is what:) the 
screen with the sprites is applied. If someone is extremely 
interested - contact me.


'Weed' features no grid and no sprite definition. We get colour
for every char and the number of sprite, if needed, right after
depacking. I just couldn't understand how to redraw sprites and
took it from the previous product. Because of that there are
163 of them, not 256:) why not 192? Some are the same, I just
erased it ...

Definition of type and sprite number at the packing stage is
simplified too. No attention paid to the char's heights colour,
everything counts with the banal moving through all variants.
Sprite, having minimal differences is the needed one. It is
logical if we are talking about machine logics - human would
choose the form appropriating one ...

You will find two sources in attachment. My_batch - my private
source designed to assemble the demo. It was used exactly in
this form. No comments, everything was done specially for our
needs. Colourful - source designed to be understood (as much as
it could). I wrote comments these days, so not laugh too much.
Also, do not pay attention at the awful code - it just works,
that counts. I really didn't know that someone would need it:)

Both are in storm assembler format. I don't know how users of
the other asms would convert it - practically it is impossible.
And I just can't write the other way now: (((

Don't be confused by the multiple repeats of some lines in some
places:) unwarping of the inner loops adversely affect the
amount and modification ability of the code, but very good on
readability and speed, simplifies the coding at last - and
sometimes I am just running out of registers ...

'Check' procedure is called before packing, it sets the screen
in the state, consumed by the packer - all empty chars coloured
ink = paper. Due to a distinctive feature of pc converter
bmp2scr, completely filled chars are not being looked for,
because it never happens.

There is another trick ... In some chars only 1-2 pixels could
be set. Fitting (wisely) sprites are not being found all the
time, resulting bugs on the screen. At the moment of party
version I went through this, adding two sprites - one completely
filled, and second - empty. That not really helped - can be
approved by peculiar people who have seen it. After the party I
wrote normal optimiser, it just cleans such chars out. 'Optim'
procedure is doing that. P_min parameter sets quantity of
threshold pixels to clean the char. Checking goes for the less
and for the larger quantity of pixels (1-2 and 62-63 pix if
p_min = 2). Setting this parameter to 32 turns the picture to
clean attributes. Some people like it that way:)))

'Check' and 'optim' are doing overlapping work, but I didn't
correct it.

Also a simple rle packer with the strange logic was used. Block
of packed data represents itself as a continuously bit field,
where commands and arguments are placed. Commands consist of two
bits, accordingly to that there could be four of them:

2000 - new colour, 3b - colour code 01 - new sprite, 8b - number
of sprite 10 - chain, 4b - chain length in 1911 - one filled 
char 

More detailed ...

Work with colour is going like that - we have two colours,
paper and ink. 'New colour' command sets new value of ink,
while paper becomes equal to an old value of ink. That scheme
proved to be more appropriate and optimal.

Sprite ... Draws sprite with the right number, colour is set by
the current values.

One filled char - ink = paper_current, paper = paper_current, 
while current colours are not changing.


Chain - sequence of filled chars. Length is set by the four 
bits, that number was chosen by the experimental way, more or 
less was found unprofitable.


I described the packing algorithm, depacking is the same. All
work is going on with structured data, being described above.
It could be written the other way, I would not be surprised if
it would be simplier and faster than my version. We just were
convenient with this work - speed of compression isn't that
high, but there is no need to compress something too often,
decompression is better - confines in three frames, opposingly 
to our delay - 5.


Except of the sources, mentioned above, you can find some
screens for testing in attachment. And a small program,
demonstrating this method, for those, who haven't seen our demo
:)))

wbw, poisoned cyberjack / / triebkraf