Speccy #06 31 августа 1996

Программирование

Programming - the effect of page turning the text on the sine.

       PROGRAMMING


 Vladimir Kuznetsov


   HaLLo! With your regular correspondent heading 
"Programming". During the summer there are many great events 
(collapsed "Omega H.C.", successfully gathering

demomeykerov "Enlight'96" with its attendant consequences from 
there, I I got me "Amiga 1200" and

dob) and accumulated a lot of ideas. C
one of which I now share with
You.

   Around since 1994 can be
found in various intruhah,
demonstrashkah and t.p.effekt page turning text sinusu.Ya'm 
sure someone of you tried to replicate this effect

(Without breaking the original), but nothing
failed because conventional methods are not suitable for this 
purpose. K this problem should be approached outside the box, 
which we now do. But to start let us agree on the allocation of 
memory: 

 # FFFF

        Second page of text
 # F000
 # EFFF

        The first page of text

 # E000

Addresses can be taken and others, but
These are chosen in order to save memory.
The principle effect is very simple:
1. Propechatyvaem first page

   (You will need to be

   make its own procedure
   fool printing character);
2. Deduce it to the screen;
3. Pauses;
4. Propechatyvaem second page;
5. Deduce it to the screen;
6. Pauses;
7. Repeat from the beginning.
We are only interested
Output buffer points to the screen.
This can be done several
ways. For example LDIR'om or
stack, and more effective in
this case is a very original method:
PUT_B: LD (P_EXIT +1), SP

        LD SP, HL

        POP HL

        LD (# 4800), HL

        POP HL

        LD (# 4802), HL

        POP HL

        LD (# 4804), HL

        .....

        POP HL

        LD (# 57FE), HL
P_EXIT: LD SP, 0

        RET
Brilliant! We killed immediately with 2
rabbits: copied buffer (to copy a single byte wasted
only 13 cycles!) and spit
on the nonlinearity of the screen! But another problem arises, 
for the copy procedure is required in exactly 2 times more 
memory than inferred buffer. It follows

conclusion: if you write so much
"Genius" program, which is not
can afford the extra
bytes, this method is not for you.
No need to fill "kopirovalku manually. You may notice that 
"kopirovalka consists of repetitive commands, therefore,

I advise you to write for such cases
installer (a procedure that
will create what you need).
Now we only need to enter
"Kopirovalki" in the register pair
HL file start address sprite, and
everything else it does itself.

   To change the screen to
calculate a table of values ​​of the cosine formula:
X = INT (64 +63.5 * COS (I * PI/64)), where
X - result
I - option (FOR I = 0 TO 127)
Correspond to the first page
values ​​for I = [0 63], and the second
page - I = [64, 127].

   I have simplified his task by using ready-sprite (disappear
procedures for printing characters
control over the position of the pointer
in a buffer and a pause between the pages). The result is a
image viewer 256 lines.


   Not to be unfounded, I
prepared a program that
demonstrates the 2 images the size of 256x256 pixels. Switching
images is done by pressing
press ENTER, and the output of the demonstration on SPACE.YA
 Attached you will find the text
programs for TASM (do not forget
download Russian font TASM.FNT
to read my comments) and
image files ROSE.DAT and CHER.
DAT (sprites size 8192 bytes)

P.S. Images (256x256), I took

     from the graphical redadaktora

     Personal Paint 6.4 (Amiga)

     and there to convert them into

     2 colors.

                     i'LL B BaCK

             SPeCiaL 4 u, Mr.Key