ZX News #02 30 ноября 1996

Программирование

How do INTRO - write the intro with the plasma and sprites.

(C) 1996 Serge Segal

 WHAT IS THE "INTRO" and how to combat it



             "In the good old tradition

     I'm going to pretend

     that all understand, and you

     'll pretend that I

     believe ... "


              (From unpublished applicant
              representations of our teachers

              Theoretical Mechanics)


                Attention!
 This article is not propaganda
product for or against the intro. The goal that it pursues, the 
reader may be identify himself.

(Prim.avt.: I doubt very much!)

 Let's begin, sir. Suppose you start spinning, fancy, some
there "CROCODILE GENA + CHEBURASHKA SOFT".

  Looking at a variety of products from
monsters of modern programming
you decide to make your own intro to
some old and anyone at ... not
required igre.Takoe desire should not be tolerated! "It is 
better to write a game!" - advises about this renowned magazine 
"Spectrofon". Helpful, I want to to another in the same vein: 
"If you want to eat, you better go to the bathroom or breathe 
deeply - in fact, too good. "  I hope you have enough is enough 
chutzpah to defying all reasonable directions people to take up 
this thankless job. 

 Okay, let's start maybe. Take, for
example, plasma. Old effect, even from
"INSULT md". And so, in this article
will be considered by my version of Plasma.

Prim.avt.: Two months later, after
I wrote this effect us in Lugansk hit game "LASER SQUAD FOR 
COVOX", in which I was surprised to see the effect

like as two peas similar to mine. His
author - Musiyenko from Zaporozhye. In order not to
was hurt, I put away its effect, but now, because of its 
clarity, simplicity and clarity, I drew it into the light God. 
I'm willing to admit that the idea - Musiyenko, and do not 
insist on their copyright. 

 The magazine is accompanied by all the sources of intro.Glavny 
principle is: the plasma is created by adding two identical 
sine waves with simultaneous shift to a different length.

 First we need to prepare a table of sine, as calculate it using
built-in calculator is too cumbersome.
 Here's a program that makes the table:

 10 FOR F = 0 TO 255: LET S = 16 + INT (16 * SIN

  (F/256 * PI * 8)): PLOT F, S: POKE (30000 + F),

   S: NEXT F
 20 RANDOMIZE USR 15619: REM: SAVE "INTR1"

   CODE 30000,256


 As you can see, the principle is simple to idiocy,
but nevrubivshihsya explain - with the help of
BASIC'a we create a table in which
Bytes take values ​​from 0 to 31, changing the on sinusoidalnoy 
dependence. This table unload the disc. The number appearing 
after the PI - the frequency factor, experiment with it.  Now 
Retrieve somewhere muzonchik, compile it (under the address is 
25003) and draw font'ik 8 * 8 (this can be done

in the Art Studio). On the disc with a magazine, you
find the font seg9.fnt and melody ZEFIR.

 Next, you need to deal with the most
program.

 To develop the principle of early withdrawal
this plasma screen. In my personal
view here LDIR not do. More logical
just keep in mind a set of sprites and
display them sequentially, one after
other, so that it looked natural. Thus everything depends on 
the memory. Let's count up: 2 / 3 of the screen - this is 4096 
bytes and free space in our 48K mode - 16384 bytes. Consequently

fit only four sprites that
few enough. Let's try to cheat:
will be displayed on both sides one third of the screen
and same sprites, but with different initial phase, it will 
give us for 8 sprites. Next - worse: making this a third mirror 
maps and get the 16 sprites! To consolidate his victory over 
the memory, we recall that the sine - a periodic function, 
therefore, cutting the screen More and vertically, we get 32 
​​sprites of 512 bytes each. And all this in one

48K page of memory!

 Now let's write a little protsedurku, which will produce 
sprites. 

 The principle is very simple: a pointer to
one place in the schedule, another - on another.
We take two bytes, add up, divide by two,
and obtain the height of a pixel, which we
should portray. For his portrayal of the procedure, we use the 
ROM 8880, which calculates its address, and then derive

it yourself.
 After the image 128 pixels pass
to fill. The method is simple: from the top
screen take bytes impose it on OR
with the lower byte and puts it in (lower) byte back to OR with 
the following (Farther down) byte.


 When the column is finished, proceed to
next. Then take a right on the screen
sprite and enter it into memory. Change the
Both the index tables of sines and repeat
32 times (the number of sprites).

 Next, we need to write a piece,
that all this brings to the screen.

 Use the so-called DECRUNCHING'a. This means that we're 
somewhere in the memory will create a program that will make a 
sprite on the screen.  We call this procedure DECRUNCH.Vot 
about what happens as a result of her work: 


     LD SP, HL

     POP HL

     LD (# 4000), HL

     LD (# 4010), HL

     LD (# 48E0), HL

     LD (# 48F0), HL

     POP HL

     LD (# 4002), HL

     LD (# 4012), HL

     LD (# 48E2), HL

     ....

     And so on ...

 Now there are very few: take care of the owners of 128k 
machines and perpetuating their own behalf.

 This requires detection
128k execute the process of creating sprites several times with 
different initial values ​​of pointers, recording results in 
different memory pages. Then do a survey of the keyboard and 
switching pages.


Prim.avt. Honestly, the only
I took out the intro Musiyenko - is the principle of separation 
of text and switch effect to it to me it somehow never 
occurred. (Of course, this change was done recently, before the 
creation of article)


 Next, we write the output text, but a simple no special 
frills. And, for greater effect, add two moving stripes.  It 
now remains to write the text and find any toy.

 The annex to the magazine you'll find a game
"RUFF 'REDDY demo", it meets all the requirements psevdonovya: 
the old, without music, and, besides, a demo version instead of 
complete.  Enumerating files:



  INTRN4.Z - source intro format

             ZX-ASM 3.0

  INTR1, INTR2, INTR3 - experimental results
             experiments with the sinuses.

  ZEFIR - Melody C. Michaell 'well compensated
             under a fixed 25003.

  seg9.fnt - shriftets by Serge Segal'a.

  RUFF'RED - game "RUFF 'REDDY demo"

 All right, now we can say: "Goodbye, AMIGA RULEZ 4EVER, ...", 
etc. and etc.


 P.S. Also appertaining creation Serge Segal hand
App. Written in the glorious city of Luhansk, September 17, 
1996 from Christmas Our Lord Sir Clive Sin ... ugh!

Jesus Christ - Antivirus ...??? AAA!
remember! Saviour ...