HPAVC/HPAVC CD-ROM.iso/TUT13.ZIP/TUT13.TXT

Text File | 1994-07-23 | 7KB | 173 lines

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

                           --==[ PART 13 ]==--



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■ Introduction

Hello again! Here I am, cooped up at home, recovering from my illness
with nothing to do, so of course it is the perfect time to write another
trainer! After the long delay between parts 11 and 12, two trainers in
two days doesn't sound like a bad idea.

This trainer is on starfields, which is by request of more then one
person. This is quite an easy effect, and you should have no trouble
grasping the concept behind it. I will be doing a 3d starfield, a
horizontal starfield is very easy with you merely incrementing a x-value
for each star for each frame. I am not even going to bother doing code
for that one (unless requested).

So I am off to go grab my antibiotics pills and I will be right back
with the tutorial! ;-)


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 Denthor, EzE, Goth, Fubar or Nobody on Connectix.
            3) Write to :  Grant Smith
                           P.O.Box 270 Kloof
                           3640
                           Natal
                           South Africa
            4) 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 ;-))
            5) Write to [e-mail] in E-Mail.
            6) Write to [e-mail]

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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■  What is a 3d starfield?

I am not even sure if I should do this bit. Go watch any episode of Star
Trek, the movies, Star Wars, or just about any sci-fi movie. Somewhere
there will be a scene where you can see stars whizzing past the
viewscreen, with the ones that are further away moving slower then the
ones that are passed quite close to.

This is a 3d starfield. If you look closely, you will see that all the
stars seem to originate from a point, the point you are travelling
towards.  This is an illusion which thankfully happens automatically,
you don't have to code for it ;)

Starfields look very nice, and can make a big difference to an otherwise
black background. It also makes a great screen saver ;-)


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■  How do they work?

This is actually quite simple. Imagine if you will, each star in the
heavens having an x,y and z coordinate, with you being at 0,0,0. Easy?
Right. Now, if you were to say move forward, ie. increase your z value,
to you you will still be at 0,0,0 , but all the stars z values would
have appeared to decrease by the exact same amount.

In easier language, we decrease the z value of all the the stars so that
they come closer to you, and eventually whizz past.

This solves all our problems. Stars that are close to us on the x and y
scales will pass us by faster then those that are very far from us on
the x and y scales. The only thing we must watch out for is that no star
is at 0,0 , ie. exactly in front of us, otherwise there will be a
collision which will not look good.


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■  How do we code this?

The first thing to be done is to generate our starfield. This is quite
easy, with us choosing x values between -160 and 160, and y values
between -100 and 100 randomly. Each z is sequentially greater for each
star so that we don't get large areas with no stars. We must remember to
check that there are no stars at 0,0!

Okay, now we start the actual viewing section. Here are the steps :

1) Convert our 3-d coords into their 2-d versions. Have a look at tut 8
   to see how this is done, but basically we divide by z.

2) Clear away all old stars that may be on the screen.

3) Draw all our stars according to our 2-d values we have calculated in
   1)

4) Move all the stars either closer to us or further away from us by
   decreasing or increasing their z values respectively.

5) If a star's z value has passed into the negative, place it at the
   very back of our "queue" so that it will come around again

6) Jump back to 1) ad-infinitum.

That is, as they say, it. In our sample program the steps have been
neatly placed into individual procedures for easy reading.


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■  What next?

Okay, so now we have a cool looking starfield. What next? How about
adding left and right motion? A menu or a scrolly in the foreground? How
about figuring out how a star tunnel works? A cool 3d routine going in
front of the stars?

A starfield can make just about any routine look just that much more
professional, and can itself be improved to be a great effect all on
it's own.


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■  In closing

So, this was yet another effect in the series. Do you still want more
effects, or what? Leave me mail with further ideas for trainers. I may
not do it if you don't ask for it!

Oh, well, the medicine has been taken, it is time for me to go. Hello to
all those people who have sent me mail, and those great guys on #coders
in IRC (you know who you are). Wow. That is the first greets I have ever
done in a trainer. Hmm. Maybe I'm just ill ;-)

Happy coding people!
  - Denthor
      19:28
        24-7-94

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  ║
║Connectix BBS             ║[phone] ║ALL  ║
║POP!                      ║[phone] ║ALL  ║
║Soul Asylum               ║[phone]  ║ALL  ║
║Wasted Image              ║407-838-4525    ║ALL  ║
╚══════════════════════════╩════════════════╩═════╝

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