(C) SerzhSoft
UC SINUS ZABABAHAT
Better in the hands of the chickadee,
than under the bed, duck!
It is time to talk about sore, and more specifically -
about the sinuses. The point that in many megademnyh effects
used exactly sinus tablets.
This can be unpretentious plasma any body moving in a smooth
trajectory, the flight over the mountains, tonnelchik
and a lot more of the other, which only
one can wish ...
Traditionally, and convenient, of course,
create a sine plate with a size
multiple of 256 bytes, or even better - just
# 0100! : -) This plate must begin with the address aligned to
a segment that is least significant byte of the address is
equal to the toe (#? 00).
Create a simple sin-table can be
using ordinary BASIC. For example,
we need a plaque, located in
address 24576 (# 6000), length 256 bytes
amplitude (scope) sine -127 to
127 and the size of one period. We get:
10 FOR i = 0 TO 255
20 POKE 24576 + i, SIN (PI/128 * i) * 127
1930 NEXT i
Now generated a plate can be stored on disk and embedded
in their assembler effects on INSERT, INCBIN and
etc.
But you decided to tweak
amplitude, say from -63 to 63, or you
suddenly knocked in the head, that "the median
point "should not be 0 and, say, 128.
That is, a scatter plate from 128-63 to 128 63. Of course, you
can again, "download" BASIC and gain a little
another program:
10 FOR i = 0 TO 255
20 POKE 24576 + i, SIN (PI/128 * i) * 63 128
1930 NEXT i
Then again, keep everything on the disk,
and continue to kodit asm'e. But perhaps even last lameru
became clear that there is something wrong. Inefficient, a
waste of time, and even space on the disk all sorts of "left"
files occupy. Plus, to ensure same Ping compile with podgruzku
on INCBIN'u. And keep a sinus period in memory when you can do
and four ... No, this must have something to do!
And the output is, of course, there is. Not really
something We weakly nakodit generation procedure
sinus in assembler. Yes, a piece of cake!
Clap, and is ready routine using ROM 'Shnogh calculator. A
similar thing present in Deja Vu # 03
article "Floating attributes. Here
is slightly improved procedure:
STACK_A EQU # 2D28
FP_TO_A EQU # 2DD5
;
SINCALC
PUSH DE
PUSH BC
PUSH DE
LD A, C
CALL STACK_A
POP DE
LD A, E
CALL STACK_A
RST # 28; calc
DB # A3; stk_pi / 2
DB # 34, # 40, # B0, # 00, # 40, # 40
DB # 05; divide
DB # 04; multiply
DB # 1F; sin
DB # 04; multiply
DB # 38; endcalc
CALL FP_TO_A
JR Z, $ +4; ->
NEG; |
POP BC; <
ADD A, B
POP DE
LD (DE), A
INC E
JR NZ, SINCALC
RET
At the entrance to the register C, we must specify the
"scope" sine (amplitude:-P ... + C), the register B - central
(How to add), and the register pair
DE must contain the address of the buffer under
plate. Moreover, this address must
must be divisible by 256 (aligned to the segment). And then,
after about 15 seconds, we get those treasured 256 bytes!
"So up-to-olgo!" - Fair notice and you're right. But what
you have like only 39 bytes of memory occupied by the
procedure. But, of course, this example was given only for
completeness paintings, and this procedure we will examine now.
After all, why would you in the demo, write "Please, wait 15
sec ... Decrunching ... "just for a plaque in 256 bytes! And
rightly so! So, here high-speed analog above procedure, which
works much faster, though he still has 55 bytes + 64 bytes
data. Total: 119 bytes. But the speed!
SINMAKE
INC C
LD HL, SIN_DAT
PUSH BC
LD B, E
LP_SMK1 PUSH HL
LD H, (HL)
LD L, B
LD A, # 08
LP_SMK2 ADD HL, HL
JR NC, $ +3
ADD HL, BC
DEC A
JR NZ, LP_SMK2
LD A, H
LD (DE), A
POP HL
INC HL
INC E
BIT 6, E
JR Z, LP_SMK1
LD H, D
LD L, E
DEC L
LD A, (HL)
LD (DE), A
INC E
LP_SMK3 LD A, (HL)
LD (DE), A
INC E
DEC L
JR NZ, LP_SMK3
LP_SMK4 LD A, (HL)
NEG
LD (DE), A
INC L
INC E
JR NZ, LP_SMK4
POP BC
LP_SMK5 LD A, (DE)
ADD A, B
LD (DE), A
INC E
JR NZ, LP_SMK5
RET
;
SIN_DAT
DB # 00, # 06, # 0D, # 13, # 19, # 1F, # 25, # 2C
DB # 32, # 38, # 3E, # 44, # 4A, # 50, # 56, # 5C
DB # 62, # 67, # 6D, # 73, # 78, # 7E, # 83, # 88
DB # 8E, # 93, # 98, # 9D, # A2, # A7, # AB, # B0
DB # B4, # B9, # BD, # C1, # C5, # C9, # CD, # D0
DB # D4, # D7, # DB, # DE, # E1, # E4, # E7, # E9
DB # EC, # EE, # F0, # F2, # F4, # F6, # F7, # F9
DB # FA, # FB, # FC, # FD, # FE, # FE, # FF, # FF
Now when you install any
Your FX'a enough to cause SINMAKE
required parameters, and after a second
plate is ready! Can generates a number of different plates ...
Or one, but consisting of different periods of sinus with
different amplitudes ... And then, say,
to put on the table scroller and torn on all cylinders ...
In the Appendix you will find the assembler
source with the two procedures. AND
remember:
Better Playing sinus
than megademe glitches!
P.S. But you can do without
plate data SIN_DAT! Who would guess -
how? : -)
