Exchange of experience - About the creation of the demonstration program "YES DEMO".

                                
                                
         EXCHANGE OF EXPERIENCE.         
                                
   This section will describe
announced the creation of a demo
programs YES DEMO.             
We will analyze the entire program: from
BASIC auxiliary
procedures to the bootloader. But before
studying the following mathematics
rial, run this program and
study it carefully in your work.
                                
ATTENTION!!! To understand the math
rial, the reader must have
some knowledge.            
                                
                                
                                
                                
                                
                                
                                
 Production of any program
starts with screen planning
On the screen, if possible, not
there should be empty space.Pacno-
position of all elements of the screensaver
must obey certain
rules (this is in particular related to
but with inconvenient organization
attributes area).  For example,
frame, same as the drawing in
center, are located strictly in the
comets. It should also be noted that
that moving program elements
we (indicators, creeping line,
flying "YES") do not overlap
at each othersince it's not
provided.                 
   The screensaver was drawn in
ART STUDIO. File in A.S. format
has the name SCREEN. To reduce
amount of memory occupied by
wow, it was compressed
and is named SCREEN+ .           
                                
SCREEN+ file length is 1562
bytes, despite the fact that the file is SCREEN
has a length of 6912 bytes.         
   The character generator (font) was
also drawn in ART STUDIO.
Character generator length - 768 bytes
96 characters of eight bytes each
This file is named ABC.fnt.    
Now let's move on to consider
BASIC block BASIC.             
  Since addressing the screen
ZX-SPECTRUM area is not very good
convenient and the program would spend
a lot of time to recalculate
coordinates, then a table is created
addresses for the second third of the screen.
This table is created by 100 - 110
BASIC program lines (during
execution of these lines, the program
shows which addresses are entered-
included in the table). The table contains
64 double-byte addresses and subsequent
Actually, it is 128 bytes long.
The table file name is TABL 01$.  
 Now a little about the flying YES
(hereinafter referred to as a sprite). Position
sprite on the screen (horizontally
ntali) to predict in advance the un-
possible, and that's why he was drawn
van (again in ART STUDIO, file
SPRITE) in all eight possible
Each sprite is size 2 by
5familiar place and length 80 bytes.
After each sprite comes its
mask. Mask required
Dima in order to
entire surroundings
sprite remained
untouched. The mask is like a cutout -
There is no room for a sprite.            
By the way, this technique is used
in all gaming programs.
And again, all eight sprites
and masks are inconveniently located for
application, therefore with the help
lines 10-40 of the BASIC program all
it was translated into another fo-
rmat, recorded under the name SPRITE+
 The sprite will be moved along the
ellipse theory. Each time, calculate
show next coordinate
trajectory would require a lot
computer time, therefore
ki 200-210 all the same program
BASIC, create a coordinate table
trajectories. In the considered pro-
gram table of coordinates contains
laughs at 101 coordinates given
in the X,Y system. Thus, ta-
blitz takes 202 bytes. Recognize
com the ends of the table are
two zeros.  Final length
tables - 204 bytes, name ELIPS.
   To write the text there were
used Z00-Z80 lines pro-
BASIC grams.  At the end of the text
stands zero - a sign of termination.
The entire message has a length516
byte and name TEXT. The music was on
written in the SOUND TRACKER editor
Melody length - 333 bytes, address
placement - Z4458, name - MUSIC.
 Let's move on to considering the
first part of the program. If you have
branded version of the magazine, then
A printout was included with the disc.
assembler demonstration.        
The writing of the program began with
manufacturing of individual sub-products
gram (hereinafter referred to as p/p). Every
It’s convenient to write p/p separately
and debug. First let's look at
p/n of the creeping line, its beginning is
line 1820. When accessing this
the following happens:       
1.shift the entire line by one pi-
  xel using SCROLL;  
2.end check         
  text (18Z0-1900);           
Z.finding the beginning of a letter in a sign
  cogenerator (1910-1960);     
4.set the bit output address
  letters and number of output
  lines (1970-1980);            
5.output of one letter bit (1990-
  2180);                        
5.1.checking how much shift is needed
  no times byte letters (2000-2040)
  Shift counter -
  SCHET7;                       
5.2.lines 2060-2070 byte shift
5.3.direct bit output
  letters (2100-2140);            
5.4.setting the next address
  screen area (2150) and following
  next address byte letter(2160);
5.5.checking for the end of output
  eighth bit of letter(2170-2180)
6.check SCHET7 onzero (2190-
  2210). If not zero, then SCHET7=
  SCHET7-1 and output (2280-2290) .
  If zero, then set
  next letter address (2220 -
  2240) and variable SCHET7(2250-
  2260).                        
P/n SCROLL (1690-1810)begins
from setting the address of the right side
the top corner of the running line and co-
number of rows to be shifted (1690-
1700).Line shift (1710-1800).
                                
   Next considered item
there will be instructions for drawing indicators
(2Z00-2680). The payment system itself uses
the same fragment (2470-
2680) six times (for drawing
six levels of indicators). For
correct operation of this part
you need to set the bottom address in HL
indicator, and in A is the register number
music coprocessor, with co-
who needs to read the current
channel amplitude. In lines (2З00-
2460) is performed six times
setting these parameters and
the INDIC fragment is used.
Lines 2470-2500 read the value
amplitude decrease, and 2510-2670 is not
the indicator is displayed,
height specified in register A.
                                
                                
                                
                                
 Color shifting along the frame
(2690-З140). This p/n is called
not at every interruption, but after
times, since in the variable SCHETb
two is installed. But in
chalefulfillment instead of deuce
the number is 190 and therefore the color
begins to mix through non-
how many seconds? Stirring pro-
proceeds like this: shift right top
horizontal (2770-2810), shift
down right vertical (2850-2950)
shift left bottom horizontal
(2970-З010), shift up left
verticals (Z070-Z120).          
   Image flicker in
center of the screen (З150-ЗЧЗО). In na-
at the beginning of this procedure there is a RET, but
he cleans up when he starts to re-
the color on the frame (2740) gets in the way. But
after replacing RET with NOP flickering
will not begin immediately, since in the
belt SCHETS costs 190
and not 2.                         
                                
    The variable (3450) stores
number of the color that will be painted
sew image.  Meaning
this variable is cyclically changed
ranges from 7 to 0.               
In lines 3280 - 3290 occurs
setting image height B=5
and addresses in the upper left corner.
Procedure (ЗЗOO-З420) produces
coloring rectangle 5 on
7 acquaintances                    
    Now about two p/p-ahs, which
work in pairs.  This is RESTOR and
WRITE. These two items serve for
output of the shuffled sprite.
The process looks like this:      
1. Overwriting previously drawn
"YES" (RESTOR);                 
2. Output of the sprite according to the new coordinates
natam trajectory (WRITE);       
H. Delay and transition to 1.At the beginning of subsection RESTOR (1080-1З80)
the height of the rubbing is set
my sprite (1080) .  In a loop
(1090-1З70) the following is repeated
translation of coordinates given in DE
to (1110-1240) with the help
second third address tables;
finding the buffer address (1250-
1280) from which will be taken
recovery information
screen; restoring a line in
five bytes (1290-1ЗЗО);  increase
vertical coordinate (1З40
-1З50); loop until
All 16 lines have been restored.
P/n WRITE has a structure similar to
I'm chewing on the RESTOR payment card.  Exactly the same
the input data is the regi-
string pair DE with vertical and
horizontal coordinates.
Only in lines 700-770 does
there is a calculation going on, which sprite is from
eight will be used, and then
everything follows the same scenario.
Lines 960-990 - immediate
displaying the sprite on the screen.         
And now the last and most pro-
flock of interrupt handling.
P/n begins with the prohibition of interruption
registration and entry of all registers into
stack (1З90-1510). Then I call-
We're mixing colors, you're
water the next part of the music and
flicker (1520-1540).After that
all registers are restored,
interruption and drainage is permitted
a refund is provided from the payment order.       
The time has come to consider "se-
rdcevin" program (1З0 - 690).
At the beginning it happenssetting
programs for work (1З0-З40), and
namely, initialization of music,
cleaning and blackening the screen, you-
splash water, buffer formation
ra second third of the screen, installation
new character generator and parameters
interruption. Then comes the main
external program cycle (Z50 - 580):
                                
1.Restoring that part of the screen
  on which it was imposed
  sprite (Z50-Z60);             
2. Calculation of the next coordinate
  you trajectories (Z70-450);      
H. Setting the coordinates of the next
  recovery (460);         
4.Calling the command line for drawing a sprite
  ticker and indicators
  (470-490);                    
5.Delay and timing (500)
6.Setting the next address
  trajectory tables (510-540);
7.Check for pressing the spacebar.
If the spacebar is not pressed, then the entire
the process is repeated from the first
point.                         
If the spacebar is pressed, then
return all system parameters
(590-660) and transition to zero
TR-DOS ROM address (670-690), i.e.
reset and start boot.            
                                
 After assembly, the machine
The code is 630 bytes long and
location address 37794, name CODE+
There are two files on the disk: one
with the name CODE, which can be
upload to GENS (which is also
attached) and a file named
CODE+, which is already ready for
use.So, that's it for the demo to work.
done. Load sequentially
files to memory:                 
                                
    address length name         
                                
    З0000 204 ELIPS       
    З0204 128 TABLO1$     
    ZOZZ2 1280 SPRITE+     
    З1612 768 ABC.fnt     
    Z2Z80 1562 SCREEN+     
    ZZ942 516 TEXT        
    Z4458 ZZZb MUSIC       
    З7794 6З0 CODE+       
Upload the file from address 30000,
8424 bytes long (name LIBRARY),
which includes all neo-
required for work.            
Now if the LIBRARY file is loaded
go to address 30000 and run
from the address Z7794, then the demonstration
will start working, but in this way
running the program is inconvenient
difficult and therefore you need to do it
loader We'll make the bootloader mono-
block (one file). For this
load the GENS code file under
address 30000; we type in BASIC
two lines:                     
1 REM...                       
2 RANDOMIZE USR VAL "23872"     
By "..." we mean 34 spaces
(that's how many bytes are required
to place the loader).     
Run GENS ( RANDOMIZE USR  
30000) and write a program to load
zchika:                          
                                
 10 ORG 23872            
 20ENT $                
 30 LD SP,29999         
 40 XOR A                
 50 LD BC,6911          
 60 LD DE,16385         
 70 LD HL,16384         
 80 LD (HL),A           
 90 LDIR                  
100 OUT (254),A          
110 LD BC,#2105         
120 LD DE,(23796)       
130 LD HL,30000         
140 CALL 15635            
150 JP 37794            
                                
We assemble and exit the assembly
Blair. Now in BASIC you can see
that after REM something is written
nonsense, this is machine code
part of the bootloader.  Take a clean one
disk and in BASIC we type:      
RANDOMIZE USR 15619:REM:SAVE "YE
S DEMO" LINE 2