Programmers - exchange of experience: On the effects on the curb, and about something else.

<b>Programmers</b> - exchange of experience: On the effects on the curb, and about something else.

 On the effects on the curb, and about something else.

music by DNK
(C) MIK 20.10.1996
_________________________________________

The idea of this article was born after reading some articles 
that were published in ZX-REVIEW dedicated BORDER effects.

 As a result of reading them, I
impression that either I went
to these issues as something wrong, or the authors of articles 
(no offense to them it is said) is not know enough on this 
topic, or hide a "secret" information. Next I will try as much 
as possible to analyze in detail the principle of creating 
these effects. Immediately apologize for what I can miss some 
little things so as to me they are obvious things. So

start:


                Chapter I.

         The most common effects.

The simplest thing that could come up with so
outright turned BASICom:

   10 BORDER 1: BORDER 2: BORDER 3:
BORDER 4: BORDER 5: GOTO 1910

The result of this action will
color bars flashing on BORDERu. Nabalovavshis this program, you 
will definitely come to the conclusion that it would be fairly 
well-to nail them tightly to certain places on BORDERe. Since 
experimentation with hammer and nails are unlikely to help,

have to consider a software solution
this simple (!) problems. But for a start
some literacy classes:
Computer all the time engaged in that
builds a picture on your (and on my
too) screen. Here's how: With the advent of human clock (simply
signal, meaning that the beam forming
the picture is in the upper left corner
screen) chip ULA (do not look for it
card if you do not have firm SPECTRUM)
begins to transmit information that
it is necessary to build. This information is
gets from two sources - the port # FE
(254), or rather of its three least significant bits
and the display area. Delaet this ULA all
time but on different computers in different ways, in most cars 
every 4 cycles CPU (more precisely a time equal to the 
implementation of four CPU clocks) is formed information in a 
special register (the registers of the processor has no 
relation) on 8 points to be construct, whether related

they have to BORDERu or to the main screen. In
PENTAGON computer to curb this
rights are not respected in the construction
its area about each point zanogo requested from the port # FE. 
Meaning the above will be explained further in analyzing the 
examples. Information is constructed by rows from top

down. On the construction of each row spent some time recording 
is strictly for the computer (usually 220 or 224 cycles). Total 
built 312 or 320 lines. It is easy to see that the number of 
cycles available to the processor, is the product of the number 
of rows on number of cycles in a row. Performance of the same 
notorious PENTAGONA - result 320 lines * 224 clock cycles in a 
row. The foregoing is repeated 50 times per second, all the 
time until konpyuter not turn off or he will not break. But 
there is another process is repeated 50 times per second, and 
attachment hardware (?) to the first - namely, interrupt 
handling.  Sovkupnost the information provided allows me to 
hope that all the legend on you will be understood.



               Chapter II.

     Firmly stoyashie stripes on bodyure

Immediately give you an example, and then explain it.


      ORG 25000

      DI

      LD HL, # B200; Set

      LD DE, # B201; second mode

      LD BC, 256; interrupt

      LD (HL), # B3

      LD A, H

      LD I, A

      LDIR

      LD A, # C9; handler is

      LD (# B3B3), A; from one team RET

      IM 2
LOOP EI

      HALT

      DI

      LD B, 255; Screen started
L1 LD A, 1; built

      OUT (# FE), A; synchronously with

      NOP; it works

      NOP; program.

      NOP; Here the first

      DJNZ L1; line.

      DEC B
L2 LD A, 2

      OUT (# FE), A; And here we draw

      NOP; second.

      NOP

      NOP

      DJNZ L2

      DEC B
L3 LD A, 3

      OUT (# FE), A; Then a third.

      NOP

      NOP

      NOP

      DJNZ L3

      DEC B
L4 LD A, 4

      OUT (# FE), A; Another.

      NOP

      NOP

      NOP

      DJNZ L4

      DEC B
L5 LD A, 5

      OUT (# FE), A; And more.

      NOP

      NOP

      NOP

      DJNZ L5

      DEC B
L6 LD A, 6

      OUT (# FE), A

      NOP

      NOP

      NOP

      DJNZ L6

      DEC B
L7 LD A, 7

      OUT (# FE), A; latter.

      NOP

      NOP

      NOP

      DJNZ L7
"LD A, # 7F; interested

      IN A, (# FE); not pressed if

      RRA; ANY KEY.

      JP C, LOOP; If not - all

      IM 1; again,

      RET; otherwise ago

                  ; TASM.
Legend:
1.Komandy NOP need to stretch the lines in magnitude.
2.Chast program located after the command HALT is possible with 
small changes to make interrupt handlers, and the band will 
work in parallel with the main program. 

3.Programma is tied in time
(The signal INT), runs every
Rebuilding the screen, and each time has the same number of 
cycles. If something remains unclear, it is still

again carefully look at the program
or (better yet) try to change it and see what happens.


               Chapter III.

          Just another chapter.

Having dealt with drawing horizontal
lines, we can take a picture of the vertical lines. But here 
waiting for a bummer: looking at a table in which

painted strokes for each team (ie in
Annex 1 of the book "How to write a game
assembly language "), you will learn that the most
Fast team work with the ports is
12 cycles CPU, which means that it does not try,
dash for 24 points does not portray. Now about the technology 
of drawing vertical lines. 

1. Throw in the port # FE any color,
such as white.

2. Immediately followed by a color that will send the 
background (black) 

3. Allow a pause equal to the number of ticks per
to construct the line in your computer, minus the number of 
cycles spent on paragraphs one and two.


4 Repeat steps 1-3

I explain with an example:

Start as in the previous example

      ............
LOOP EI

      HALT
; On entirely different

      LD D, 7

      LD E, 0

      LD A, 80

      LD C, # FE

MAX OUT (C), D; 12 cycles

      OUT (C), E; 12 cycles

      OUT (C), D; 12 cycles

      OUT (C), E; 12 cycles

      OUT (C), D; 12 cycles

      OUT (C), E; 12 cycles

      OUT (C), D; 12 cycles

      OUT (C), E; 12 cycles

      OUT (C), D; 12 cycles

      OUT (C), E; 12 cycles

      OUT (C), D; 12 cycles

      OUT (C), E; 12 cycles

      OUT (C), D; 12 cycles

      OUT (C), E; 12 cycles

      OUT (C), D; 12 cycles

      OUT (C), E; 12 cycles

      , Total has 192 cycles

      NOP; 4 stroke

      NOP; 4 stroke

      NOP; 4 stroke

      DEC A; 4 stroke

      JR NZ, MAX; 12 cycles

  , Ran up a total 220 cycles is

  ; As much as time spent

  ; My computer to build a

  ; Line

      LD A, # 7F

      IN A, (# FE)

      RRA

      JP C, LOOP

      IM 1

      RET
Theoretically, after starting the program you must
a vertical strip at the top of the screen, if the two are 
canted to one side then change number NORov inside the loop 
(Increase or decrease). The variant of the bands

will be brutally twitch (if
You PENTAGON, then it never will be)
out of this situation is as follows: insert
after HALTa team (or teams) are satisfied for the time is not a 
multiple of 4-th cycle. For example, try:

LD A, (0) 13 cycles 3 * 4 +1
or
DEC DE 6 cycles 4 +2
or
ADC A, (HL) 7 clocks 4 +3
Will certainly help!

In fact, on the curb the effects of speaking
nothing more. A final note: after the arrival of the signal INT 
management interrupt handler will be passed immediately (If INT 
came in the command HALT) or after a short delay (Duration 
depends on the number of ticks remaining for the current 
command to execute). 

That's all.

If you have anything to add on this
question, write to the editor and share your knowledge.