HPAVC/HPAVC CD-ROM.iso/pc/TUT17.ZIP/TUT17.TXT

Text File | 1995-01-19 | 10.4 KB | 257 lines

                   ╒═══════════════════════════════╕
                   │         W E L C O M E         │
                   │  To the VGA Trainer Program   │ │
                   │              By               │ │
                   │      DENTHOR of ASPHYXIA      │ │ │
                   ╘═══════════════════════════════╛ │ │
                     ────────────────────────────────┘ │
                       ────────────────────────────────┘

                           --==[ PART 17 ]==--



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■ Introduction

Hi there everybody. It's a new year, but the parties are over and it's time
to get coding again!

My mailserver died. Various sysadmins decided it was time to upgrade the
OS, and wound up nuking the hard drive :-( ... this means that request-list
is not working at the moment, and I have probably lost lots of mail.

[e-mail] is still the account to write to, and
hopefully the mailserver will be back up in the near future.

There are various C/C++ conversions of my trainer, best of which seem to be
those by Snowman ... he runs through the text files with C++ updates (and
seems to point out my previous mistakes with glee ;-), as well is giving a
fully documented C++ conversion of the source ... very nice stuff.

Also, my trainers are being put on a World Wide Web site ... it is still
under construction, but go to http://www.cit.gu.edu.au/~rwong
my site is at http://goth.vironix.co.za/~denthor ... it is currently pretty
awful, anyone want to write a nice one for me? ;)

I have just about finished Asphyxia's new game, I will let you all know
when it is completed.

Tut 16 dies with large bitmaps ... the way to sort this out is to decrease
the accuracy of the fixed point from 256 to 128 ... then you can have
bitmaps up to 512 pixels wide. I will be putting an updated scale routine
in the gfx4.pas unit.

This tutor is on a few demo effects (pixel morphs and static) ... after
this one, I will go on to more theory ... perhaps some more 3d stuff, such
as gourad shading etc. Comments?


If you would like to contact me, or the team, there are many ways you
can do it : 1) Write a message to Grant Smith/Denthor/Asphyxia in private mail
                  on the ASPHYXIA BBS.
            2) Write to :  Grant Smith
                           P.O.Box 270 Kloof
                           3640
                           Natal
                           South Africa
            3) Call me (Grant Smith) at (031) 73 2129 (leave a message if you
                  call during varsity). Call [phone] if you call
                  from outside South Africa. (It's YOUR phone bill ;-))
            4) Write to [e-mail] in E-Mail.
            5) Write to [e-mail] to get to all of
               us at once.

NB : If you are a representative of a company or BBS, and want ASPHYXIA
       to do you a demo, leave mail to me; we can discuss it.
NNB : If you have done/attempted a demo, SEND IT TO ME! We are feeling
        quite lonely and want to meet/help out/exchange code with other demo
        groups. What do you have to lose? Leave a message here and we can work
        out how to transfer it. We really want to hear from you!

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■  Pixel Morphing

Have you ever lain down on your back in the grass and looked up at the
cloudy sky? If you have, you have probably seen the clouds move together
and create wonderful shapes ... that cloud plus that cloud together make a
whale ... a ship ... a face etc.

We can't quite outdo mother nature, but we can sure give it a shot. The
effect I am going to show you is where various pixels at different starting
points move together and create an overall picture.

The theory behind it is simple : Each pixel has bits of data associated
with it, most important of which is as follows :

This is my color
This is where I am
This is where I want to be.

The pixel, keeping it's color, goes from where it is to where it wants to
be. Our main problem is _how_ it moves from where it is to where it wants
to be. A obvious approach would be to say "If it's destination is above it,
decrement it's y value, if the destination is to the left, decrement it's x
value and so on."

This would be bad. The pixel would only ever move at set angles, as you can
see below :

                Dest   O-----------------\
                                           \  <--- Path
                                             \
                                               \
                                                O Source

Doesn't look very nice, does it? The pixels would also take different times
to get to their destination, whereas we want them to reach their points at
the same time, ie :

     Dest 1   O-------------------------------O Source 1
     Dest 2   O-----------------O Source 2

Pixels 1 and 2 must get to their destinations at the same time for the best
effect. The way this is done by defining the number of frames or "hops"
needed to get from source to destination. For example, we could tell pixel
one it is allowed 64 hops to get to it's destination, and the same for
point 2, and they would both arrive at the same time, even though pixel 2
is closer.

The next question, it how do we move the pixels in a straight line? This is
easier then you think...

Let us assume that for each pixel, x1,y1 is where it is, and x2,y2 is where
it wants to be.

   (x2-x1) = The distance on the X axis between the two points
   (y2-y1) = The distance on the Y axis between the two points

If we do the following :

  dx := (x2-x1)/64;

we come out with a value in dx wich is very useful. If we added dx to x1 64
times, the result would be x2! Let us check...

  dx = (x2-x1)/64
  dx*64 = x2-x1         { Multiply both sides by 64 }
  dx*64+x1 = x2         { Add x1 to both sides }

This is high school math stuff, and is pretty self explanitory. So what we
have is the x movement for every frame that the pixel has to undergo. We
find the y movement in the same manner.

  dy := (y2-y1)/64;

So our program is as follows :

  Set x1,y1 and x2,y2 values
  dx:= (x2-x1)/64;
  dy:= (y2-y1)/64;

  for loop1:=1 to 64 do BEGIN
    putpixel (x1,y1)
    wait;
    clear pixel (x1,y1);
    x1:=x1+dx;
    y1:=y1+dy;
  END;

If there was a compiler that could use the above pseudocode, it would move
the pixel from x1,y1 to x2,y2 in 64 steps.

So, what we do is set up an array of many pixels with this information, and
move them all at once ... viola, we have pixel morphing! It is usually best
to use a bitmap which defines the color and destination of the pixels, then
randomly scatter them around the screen.

Why not use pixel morphing on a base object in 3d? It would be the work of
a moment to add in a Z axis to the above.

The sample program uses fixed point math in order to achieve high speeds,
but it is basically the above algorithm.


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■  Static

A static screen was one of the first effects Asphyxia ever did. We never
actually released it because we couldn't find anywhere it would fit. Maybe
you can.

The easiest way to get a sreen of static is to tune your TV into an unused
station ... you even get the cool noise effect too. Those people who build
TV's really know how to code ;-)

For us on a PC however, it is not as easy to generate a screen full of
static (unless you desperately need a new monitor)

What we do is this :

Set colors 1-16 to various shades of grey.
Fill the screen up with random pixels between colors 1 and 16
Rotate the pallette of colors 1 to 16.

That's it! You have a screenfull of static! To get two images in one static
screen, all you need to do is fade up/down the specific colors you are
using for static in one of the images.

A nice thing about a static screen is that it is just pallette rotations
... you can do lots of things in the foreground at the same time (such as a
scroller).

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■  In closing

Well, that is about it ... as I say, I will be doing more theory stuff in
future, as individual demo effects can be thought up if you know the base
stuff.

Note the putpixel in this GFX3.PAS unit ... it is _very_ fast .. but
remember, just calling a procedure eats clock ticks... so imbed putpixels
in your code if you need them. Most of the time a putpixel is not needed
though.

PCGPE ][ will be out on the 10th of Feburary. All the new tutors will be on
it (if you aren't reading this from it right now! ;-) ... grab a copy of
it, it is a very useful ting to have handy.

I have found out that these tutors have been distributed inside paper
magazines ... please remember that Denthor and Asphyxia retain full
copyright to the series (as mentioned earlier in the series), and if you
want to use a version in a magazine, CONTACT ME FIRST ... I will probably
also modify it/cut out various unneccesary things ... other then that, you
must not alter the files without my permission, or at least leave a copy of
the origional with the update. Maybe I could even start up a nice column
for some magazine or other :)

Sorry 'bout that, but it had to be said ...

I am writing a column for the Demuan list, a Florida-based electronic
magazine ... pick it up off ftp.eng.ufl.edu ... I have written various
articles, all bordering on quote-like design.

There are more BBS's to be added to the list at the end, but I don't have
them here... this tut has taken long enough ;-)

Byeeeee....
  - Denthor

The following are official ASPHYXIA distribution sites :

╔══════════════════════════╦════════════════╦═════╗
║BBS Name                  ║Telephone No.   ║Open ║
╠══════════════════════════╬════════════════╬═════╣
║ASPHYXIA BBS #1           ║[phone] ║ALL  ║
║ASPHYXIA BBS #2           ║[phone] ║ALL  ║
║C-Spam BBS                ║410-531-5886    ║ALL  ║
║POP!                      ║[phone] ║ALL  ║
║Soul Asylum               ║[phone]  ║ALL  ║
║Wasted Image              ║407-838-4525    ║ALL  ║
║Reckless Life             ║351-01-716 67 58║ALL  ║
║Mach 5 BBS                ║[phone] ║ALL  ║
╚══════════════════════════╩════════════════╩═════╝

Leave me mail if you want to become an official Asphyxia BBS
distribution site.