(C) Saruman / Dementia corp.
Well, that was another demo-party,
Enlight-97, and again vylilo on the heads of the poor users a
bunch of cool and clever demos. A poor user sits, looks at
them, and nothing at all, then it is not clear: how all this
can be possible? But possible, and the proof here it is - before
eyes.
This is a small tip may serve as a
starting point for a series of articles in which I try to tell
a little about demomeykinge, his techniques and algorithms. Of
course, I do not such a cool coder as Rst7, Max Iwamoto,
Exploder, etc., but what I know - that little talk. I will be
wildly happy if my work will help to write at least one
distinct bend. And because it is best to start from the
beginning, then today's topic will
Rapid withdrawal schedules through the stack
- You know, I have on screen
wounds displayed 300
sprites in a single transformation
on closing, and I can not
get rid of the scintillation
of. Help!
- Now you someone
advise you to withdraw them
the stack. ;-)
From the correspondence
in the FIDO
Perhaps the reader will carefully tracking
for all electronic media, indignantly
exclaim: "How much can you talk about it ?!?!?" How long does
it! Once more there are demos with sprites and trembling
glyuchaschimi effects (as they appear!), Then says not enough.
Thus, the basic idea behind this
method is as follows:
The command execution time
LD A, (reg) 7
LD (reg), A 7
INC reg 6
DEC reg 6
LD HL, (ADDR) 16
LD (ADDR), HL 16
POP reg 10!
PUSH reg 11!
LD SP, nnnn 10
So, what do we see? For the transfer of two
bytes in the right place, we have three ways:
a) use the register A. That is, we have
about this piece of code:
LD A, (HL)
LD (DE), A
INC HL
INC DE
Total 26 * 2 = 52 cycles. Ouch ... Mnogova
then!
b) Use register pair HL:
LD HL, (ADDR)
LD (ADDR), HL
Total 16 +16 = 32 clocks plus time of
change in ADDR. That is too much ...
c) use the operations PUSH and POP:
LD SP, nnnn
POP HL
....
LD SP, nnnn
PUSH HL
....
You say: "What is the best
way, if it takes as much time with 41! "But
I have not knowingly put in the code dots.
Think of the action teams PUSH and POP: with
PUSH is entering the value of the register address contained in
SP, and decrease the value of SP at 2, with POP - on the
contrary, these accrue from memory, and SP increases. And since
we have as many as 10 register pairs, then we can set the stack
only once for 20 bytes. The final code looks like this:
LD SP, addr; SP = sprite_adr
POP AF; H
POP BC; and
POP DE; m
POP HL; and
POP IX; e
POP IY; m
EX AF, AF '; with
EXX; n
POP AF; p
POP BC; and
POP DE; th
POP HL; m
LD (SP_1 +1), SP; Save SP
LD SP, addr; SP = screen_adr
PUSH HL; In
PUSH DE; s
PUSH BC; in
PUSH AF; of
EX AF, AF '; g
EXX; and
PUSH IY; m
PUSH IX; n
PUSH HL; p
PUSH DE; and
PUSH BC; th
PUSH AF; m
LD (SP_2 +1), SP; save SP
SP_1 LD SP, 0000; SP = sprite_adr
............ ; Again reading
............ ; Data
SP_2 LD SP, 0000; SP = screen_adr
............ ; Again conclude
etc.
Subtotal get 302/10 = 2.30 cycles for two
Bytes!
As can be seen, the difference is palpable, especially when
withdrawal of large amounts of graphics. For maximum speed
dostizheiya better to do without any cycles, and show more
the whole sprite.
Now we discuss some useful
techniques that can help you.
Often, especially in the demos, the picture consists of
several repetitions of one and the same part. In this case, by
itself, enough once considered this part, and then throw it to
the screen the desired number of times. If you need to print a
sprite with a mask, it is often convenient to proceed as
follows as follows: sprite store in memory mixed with a mask,
and read at the same time and then, and more. Example:
LD SP, data_adr; address sprite
LD DE, scr_adr; address screen
POP BC; B = mask, C = sprite
LD A, (DE)
AND B; A AND mask
OR C; A OR sprite
LD (DE), A
It is this way, slightly modified, used to display the cursor
in the journal. The cursor is stored as two 2_bayta_dannyh
_bayta_maski. Before displaying the mask and sprite is shifted
to the desired number of bits and received _three_ byte sprite
rush on the screen. As you can see, everything works without
flickering and glitches!
Oh, and all things that can be anywhere on the screen and still
and move (different cursors jumping
Smileys, etc.) need to show the very first to play music,
converting coordinates, etc. Otherwise, even if you have
everything working perfectly, can be caught any inhibitory
complex, where the sprite begins to shake and flicker. Do not
forget about this!
A Whereupon I say goodbye today, if there are any questions,
suggestions or proposal, then you can contact
me by phone 54-01-70 (ask Oleg)
or at the addresses given in Section
"Editorial." Bye!!!
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