RUSH #01 29 мая 1999

Программирование

Spectrum programming - Modern methods of coding and modern ways of working with graphics.

 COMMITTED AND MODERN METHODS Coding

         WAYS OF WORKING WITH GRAPHICS


    Year after year, to organize SPECCY
new groups, write programs. This means that somewhere there are 
more and The new musicians, artists, and of course the same

programmers who want to make
something interesting, never seen before and
not surpassed. Somewhere in the future sitting
RST # 7'ye, IMP'y, STALKER'y ... Learn assembler, day and 
night, armed with STS ' om, dismantle brick by brick program of 
his predecessors. 

    To help them all to save
weeks and months that we had
sit for the listings of programs, and
case fighting off the ever-present bugs, inventing something 
that already many have long known doing what until recently was 
considered impossible, and prepared the following material. It 
contains diverse coding tips, from very basic procedures to 
more sophisticated and effective. 

    An earlier version of this text is
Once published in an electronic journal
"Depth 1" who has not received sufficient
proliferation. Here you can see its enlarged version. I'm going 
to continue the topic in the next room, describing

useful procedures and methods of coding.


    So, we go strictly to the topic ...


1. Consider the most frequently used
methods of display images on the screen.

 a). The easiest way to get the sprite -

    to throw it consistently

    byte by byte, line by line.

    proramma, take such actions,

    looks like this:


       LOOP1 PUSH BC

               PUSH HL

       LOOP2 LD A, (DE)

               INC DE

               LD (HL), A

               INC L

               DJNZ LOOP2

               POP HL

               CALL DOWN_HL

               POP BC

               DEC C

               JR NZ, LOOP1

               RET


      DE-address of the sprite in memory,

      HL-address in the screen,

      B-width of the sprite in the familiarity,

      C-height of the sprite in pixels.

      DOWN_HL - go to the line below.

 This method, despite its simplicity
 and primitive, quite suitable for you water a static (fixed) 
graphics.  Changing the input parameters in registers

 HL, DE, BC, we can derive a picture of any
 size at any position on the screen. Unfortunately Niya, such 
flexibility is not common to all  other ways of graphics output.


 b). Display graphics with a fixed

     wide.


    LOOP1 PUSH DE

            LDI; Number of independent

            ... , The width of the sprite.

            POP DE

            EX AF, AF '

            CALL DOWN_DE

            EX AF, AF '

            DEC A

            JR NZ, LOOP1

            RET

     HL-mail sprite in memory,

     DE-e in the screen,

     A-height of the sprite in pixels.

 This method is somewhat faster than of the previous, but 
because of binding to a specific  width of the sprite, however 
raspostranen. 

 cent.) Output graphics using the stack.

     This and the following methods of inference graph
     graphs are more efficient and faster

     Compared with the previous ones, but together

     order and more complicated.

     So, sending glass screen:

     The program creates when you first start

     operating unit, which actually

     will be engaged in redeployment schedules.


     Address entered in the register graphic SP,

     then the value from the stack sequence
     Indeed extracted and entered into the equivalent
     wounds. Approximately it will vygldet this:


     ...

     POP HL

     LD (# 4000), HL

     POP HL

     LD (# 4002), HL

     POP HL

     LD (# 4004), HL

     ...


        Naturally, the address to which

     would throw the schedule in advance

     fixed, and once fiksirvany
     measures sprite. Length of the obtained procedure
     dures in the memory depends on the size

     sprite, and will be twice as large

     than he. That is, if you perebrasy
     is called a sprite on the screen (6144b.)

     size of the program will be - 12288b.

         Such a waste of perfectly

     justified, since the rate of work
     you this program is much higher than

     earlier. One byte throws
     Camping for 13 cycles. Moreover, that before

     installation program will take

     only some 100 bytes.

 g). The next method is similar to prdyduschy,

     but more suitable for scrolling

     up and down, than to display graphics.

     As to specific addresses here

     binds both the source and receiver.


     ...

     LD HL, (# 4100)

     LD (# 4000), HL

     LD HL, (# 4102)

     LD (# 4002), HL

     LD HL, (# 4104)

     LD (# 4004), HL

     ...


     Absolutely do not use the stack and not

     modifies the registers, except for HL.

     Uses for each of thrown

     B charts three bytes of memory.

     One byte is thrown for 16 so
     Comrade.

 e). The fastest way Scrolling

     screen vertically and quite Sauveur
     shennym by the graphics output of the PA
     myati is the following:


     ...

     LD SP, e-source

     POP HL

     POP DE

     POP BC

     POP AF

     POP IX

     POP IY

     EXX

     POP HL

     POP DE

     POP BC


     LD SP, e-Objective

     PUSH BC

     PUSH DE

     PUSH HL

     EXX

     PUSH IY

     PUSH IX

     PUSH AF

     PUSH BC

     PUSH DE

     PUSH HL

     ...


     This method is very effective, but

     still can not bring the whole screen

     per interrupt.

 e). Now consider the most perfect and

     under-utilized method of deriving the graph
     Key:

     These are mixed with the program,

     and obtained design types:


     ...

     LD SP, the address in the screen

     LD HL, two bytes of graphics

     PUSH HL

     LD HL, next two bytes

     PUSH HL

     LD HL, next two bytes

     PUSH HL

     ...


     Now let's take a count ...


     LD HL, number - 10 cycles

     PUSH HL - 11 clock cycles.

     To display full-screen images are not
     necessary to repeat this snippet

     3072 times = 21 * 3072 = 64512 cycles.

     LD SP, the number of - 10 bars.

     The stack will have to change (although not

     required) before the conclusion of each

     line that is 192 times = 10 * 192 =

     = 1920 cycles.

        And, all as a whole will take

     64,512 1920 = 66,432 cycles!


    As you see, is quite realistic to deduce
image without repetition of the whole screen
per interrupt.

    This method of graphics output is not
new and coined not by me. Anyway
they used a lot of my friends from the RUSH,
and told me about it some more IMP
years ago ...

    When using this method also
 consumes two bytes of memory on each dy of bytes of graphics. 
Conclusion noekrannoy sex pictures absolutely free types 
toryayuschihsya fragments elementary UCLA embedded not only in 
the Pentagon on closing the limit, but also in an interrupt on 
any normal car, for example, SCORPION, PROFI  etc. True to the 
original car will appear lyayutsya problems related to the fact 
that  there are separate fields of memory, that is equivalent 
to rannaya memory operates much slower  but we have to put the 
stack into the screen ...  But if the brand was re SPECCY 
exponentially 70,000 cycles per interrupt all of the personally 
managed to work, even it remains a place for music. 

      To make the image move camping, will have to change the 
address entered in  SP, but it's real.



    And a few more tips for
coders, who were drawn from many years of experience in 
assembly language as my personal as well as many other coders:



     When images of the mask
sprite, it's best to keep stirred
with a mask. Bytes of graphics, then the byte mask
etc. Displayed a sprite will be as follows:

       ...

       POP DE; two bytes grfiki

       LD A, D

       AND (HL)

       OR E

       LD (HL), A

       INC L

       ...
Stack when it should point to the schedule,
and HL on the screen.



     The quickest way to clear the screen:

       LD SP, # 5800

       LD BC, 0

       PUSH BC - repeat 3072 times.

You can also clean up any area in memory, etc. Of course not 
necessarily make such a procedure is absolutely no cycles. For 
example, we make only 256 PUSH'ey, and loop the block desired 
Number of times. Specific loss in speed will not.




     Now a very important thing
should be aware of all those who decided to write a quality 
program SPECCY. In the derivation of a large number of graphs, 
the probability that the television beam intersects the 
inferred currently block graphics are great. This will lead to 
the fact that at the intersection with the ray, dynamic image 
will diskrirovat. For example, when scrolling a large movie 
screen the upper part of his will be shifted, then a ray of 
"catch up" the place of withdrawal, and further half a picture 
will be output with a lag of one frame. Even more terrible 
picture is obtained if the image on the screen vremmenno erased 
scan can get it at such a moment, and then may appear

disappearing sprites promigivayuschie cursors
and other leymerstvo.

     How to deal with it:
You can try to sweep does not overlap with the conclusion 
throughout interrupts. So, you can first take

graphics in the middle and lower third of the screen,
but in the end, when luch has held the top half of the screen, 
one can derive the upper third. This method is often used, but 
because of huge differences in design of computers scan for 
different types of SPECCY may differ, that will cause 
diskrirovaniya image. Worth seeing how it works "SHOCK" at the 
Pentagon, and it all becomes clear. 

     The most effective and practical method in this case is to 
use additional screen machines 128k RAM and more. The presence 
of two screens which can be switched instantly when

using a single OUT'a very
greatly simplifies the programmer lives.

     Working with two screens is
as follows: for termination (optional) hangs a small program
which in turn connects then 7 page and normal screen, then 5 
pages and shadow screen. It may look like this:


SCREEN_CHANGER:

SCR LD A, # 55,% 01010101

        RRCA

        LD (SCR +1), A

        LD A, # 17, 16, 7

        JR C, PAGER

        LD A, # 1D; 24 +5
PAGER:

        LD BC, # 7FFD; 32765

        OUT (C), A

        RET


     All procedures, working with the screen,
should be written with the expectation that
screen is now not address # 4000
(16384 dec), and from the address # C000 (49152 dec).
Procedure DOWN_HL not need to change it and
so it will work correctly.

     The essence of this method is
that change (erase, move, etc.) you
will not the screen, which displays
currently on display, but one that resides in memory and not 
visible to the viewer. No, diskrirovaniya not be absolute, even 
if you change the whole entire screen. Thus, for example made 
in the Slovak demo "ECHOLOGY", and it is great works on all 
machines INCL. Pentagon MULTICOLOR'ov except, of course.

By the way, MULTICOLOR - this is diskrirovanie ...

      Of course to write programs using
One screen - is steeper, but in practice it
not appropriate. I advise you not to torture
users to write and soft under the two screens.



      And now the council has no direct
attitude to work with dynamic graphics, but it may be useful to 
you in If you do not have enough CPU time to play music, and 
free memory is a lot. In this the case can proceed as follows:


      Music decomposed into components and then played passing 
player. Simple data output ports will take some some 300 bars,

if you compare that player to "ASM"
requires over 8000 cycles - the difference is palpable.

      It is advisable not to load is spread out on the data 
from CD music, but to create it yourself before you start 
program, so as the size of the resulting data block can reach 
tens of killobayt. You can also try to compress the repeating 
fragments. 

      This method has been used in many demonstrations - 
"ECSTASY", "SHOCK", "SATISFACTION", "INSULT" etc.




      But the most beautiful and compact way to mute the sound 
on AY, which I saw (he wrote it not me):


SHUT_UP:

          LD HL, # 000D
SHUT1 LD BC, # FFFD

          OUT (C), L

          LD B, # BF

          OUT (C), H

          DEC L

          JR NZ, SHUT1

          RET



    In the case where you need to identify pressing any key, 
including Caps Shift and Simbol Shift is very convenient

use of "classical" procedure of
ROM, which is located at decimal address 654. The procedure 
returns the register E code 255 (# FF), if you do not press any

key.


    Example of use:

WAIT:

        CALL 654

        INC E

        JR Z, WAIT

        RET



      If someone does not understand what I am
meant by procedure or DOWN_HL
DOWN_DE, I quote below the text:

DOWN_HL:

          INC H

          LD A, H

          AND 7

          RET NZ

          LD A, L

          ADD A, # 20

          LD L, A

          RET C

          LD A, H

          SUB 8

          LD H, A

          RET

DOWN_DE:

          INC D

          LD A, D

          AND 7

          RET NZ

          LD A, E

          ADD A, # 20

          LD E, A

          RET C

          LD A, D

          SUB 8

          LD D, A

          RET



   If you need to fall down on the whole
familiarity, follow these steps (the address in HL), and not to 
call eight times in a cycle DOWN_HL, as some

naive guys ... :

LOWER_HL:

          LD A, L

          ADD A, # 20

          LD L, A

          RET NC

          LD A, H

          ADD A, 8

          LD H, A

          RET



   Sometimes it is necessary to recalculate the address in
screen at the address corresponding to this
familiarity of the attributes. Make
This can be as follows:

SCR_ATR:

          LD A, H

          RRCA

          RRCA

          RRCA

          AND 3

          OR # 58

          LD H, A

          RET



    Enough for today ... Sure ways to improve programs
may be infinite. For
each case has its own techniques and tricks. They need to know 
not only to write Killer

effects ...

      Not being able to enjoy the benefits of
advanced encoders, you can not write
dynamic quality toys, and
good system can not write a program, using the methods of a 
decade Period.


     Therefore, go for it! May soon
You can write full-screen multicolor or even some miracle 
coding! 


              Good luck!!!