screen effects - Running a string of R-Type.

<b>screen effects</b> - Running a string of R-Type.

      Ground effect



   In search of original effects turn to what is already
created. Indeed, there is no need
reinvent the wheel. For
examples not far to seek.
Game programs - it is such
storehouse of ideas that we can take
and any "untwist" it up
infinity. You will find so many little tricks that last a long 
time. Do not even need to "get into the wilderness" of the 
program, you can take what is on the surface. By repeating the 
proposed programs you will inevitably new ideas and you can 
come up with something really new. 

   Now we'll talk about code snippets - a procedure that would 
allow for a variety of original effects in programs associated 
with cleaning or drawing of the screen text output. All 
procedures listed below, the "pull" of the specific

game programs. With emphasis
was not made on the academic
side of the issue, that is not on
how does this procedure
but on an entirely practical, then
is how to reproduce a particular effect in his program.
This led to the fact that in the initial procedures performed 
certain changes of addresses and address some other points that 
allow blocks of code operate completely independently. So those 
who want to use them in their programs that will only write and 
run them. For all procedures are BASIC programs to get the 
proposed block codes for recording on a tape recorder and for 
the program's demonstration. Owners BETADISK interfaces 
(TR-DOS) themselves will be able to SAVE or LOAD substitute the 
standard prefix "RANDOMIZE USR 15619: REM:".

A few words to the BASIC program for block codes.
In line 10, after the DATA set
the following parameters: the value
RAMTOP, the name of the block codes used in the tape recording,
load address and length of the block codes. Actually codes for 
a set of are in the DATA lines to 100.



             R-TYPE


   The game begins with a ticker at the bottom of the screen. 
Character height - double, moving lines - smooth, with

increments of 1 pixel.


   Here is a slightly modified (with
to unite into a continuous
block) listing of this procedure:
1423.

   8CC0 21858D LD HL, # 8D85

   8CC3 CDCD8C CALL # 8CCD

   8CC6 21658D LD HL, # 8D65

   8CC9 CDCD8C CALL # 8CCD

   8CCC C9 RET
--------------------------
   8CCD CB7E BIT 7, (HL)

   8CCF C0 RET NZ

   8CD0 CBFE SET 7, (HL)

   8CD2 E5 PUSH HL

   8CD3 011F16 LD BC, # 161F

   8CD6 CD0F8D CALL # 8D0F

   8CD9 0604 LD B, # 04

   8CDB C5 PUSH BC

   8CDC 21DF50 LD HL, # 50DF

   8CDF CDFE8C CALL # 8CFE

   8CE2 21FF50 LD HL, # 50FF

   8CE5 CDFE8C CALL # 8CFE

   8CE8 21DF50 LD HL, # 50DF

   8CEB CDFE8C CALL # 8CFE

   8CEE 21FF50 LD HL, # 50FF

   8CF1 CDFE8C CALL # 8CFE

   8CF4 76 HALT

   8CF5 C1 POP BC

   8CF6 10E3 DJNZ # 8CDB

   8CF8 E1 POP HL

   8CF9 CBBE RES 7, (HL)

   8CFB 23 INC HL

   8CFC 18CF JR # 8CCD
--------------------------------
   8CFE 0E08 LD C, # 2008

   8D00 E5 PUSH HL

   8D01 0620 LD B, # 20

   8D03 A7 AND A

   8D04 CB16 RL (HL)

   8D06 2B DEC HL

   8D07 10FB DJNZ # 8D04

   8D09 E1 POP HL

   8D0A 24 INC H

   8D0B 0D DEC C

   8D0C 20F2 JR NZ, # 8D00

   8D0E C9 RET
--------------------------------
   8D0F 7E LD A, (HL)

   8D10 E67F AND # 7F

   8D12 E5 PUSH HL

   8D13 2600 LD H, # 2000

   8D15 6F LD L, A

   8D16 29 ADD HL, HL

   8D17 29 ADD HL, HL

   8D18 29 ADD HL, HL

   8D19 11003C LD DE, # 3C00

   8D1C 19 ADD HL, DE

   8D1D 78 LD A, B

   8D1E E6F8 AND # F8

   8D20 C640 ADD A, # 40

   8D22 57 LD D, A

   8D23 78 LD A, B

   8D24 E607 AND # 07

   8D26 0F RRCA

   8D27 0F RRCA

   8D28 0F RRCA

   8D29 81 ADD A, C

   8D2A 5F LD E, A

   8D2B C5 PUSH BC

   8D2C 3A648D LD A, (# 8D64)

   8D2F A7 AND A

   8D30 280A JR Z, # 8D3C

   8D32 0608 LD B, # 08

   8D34 7E LD A, (HL)

   8D35 12 LD (DE), A

   8D36 14 INC D

   8D37 23 INC HL

   8D38 10FA DJNZ # 8D34

   8D3A 1814 JR # 8D50

   8D3C 7A LD A, D

   8D3D 08 EX AF, AF '

   8D3E CD598D CALL # 8D59

   8D41 08 EX AF, AF '

   8D42 57 LD D, A

   8D43 7B LD A, E

   8D44 C620 ADD A, # 20

   8D46 5F LD E, A

   8D47 3004 JR NC, # 8D4D

   8D49 7A LD A, D

   8D4A C608 ADD A, # 08

   8D4C 57 LD D, A

   8D4D CD598D CALL # 8D59

   8D50 C1 POP BC

   8D51 0C INC C

   8D52 E1 POP HL

   8D53 CB7E BIT 7, (HL)

   8D55 23 INC HL

   8D56 C0 RET NZ

   8D57 18B6 JR # 8D0F
-------------------------------
   8D59 0604 LD B, # 04

   8D5B 7E LD A, (HL)

   8D5C 12 LD (DE), A

   8D5D 1914 INC D

   8D5E 1912 LD (DE), A

   8D5F 1914 INC D

   8D60 23 INC HL

   8D61 10F8 DJNZ # 8D5B

   8D63 C9 RET
-------------------------------
   8D64 00 mode (height)
-------------------------------
   8D65 ... Text Ticker
2

   Starts running line with
load address 8CC0H (36,032).
Calling procedure (8CC0H -
8CCCH), incidentally, may be
elsewhere in your program. In the register HL is given by
starting address of text messages, then there is a procedure 
call running line. This can happen many times from different 
places in your program. When Moreover, every text message

must finish printing 32
spaces at the end, this will prevent stop scrolling text on
mid-sentence. "Generally need 31 spaces, as the latter 
familiarity is automatically cleared when the horizontal

scrolling. If the running line
invoked many times, it
creates a significant amount of memory.
Therefore, printing 31 spaces allocated in a separate part, it 
should be performed whenever the print text. This you can see 
at 8CC6H. 

   Text messages are to address 8D65H (36,197). In
the end of each text message to be delivered end mark - any 
number included seven beats. For example, just FFH (255). 

   Proper procedure "is running
Line "(8CCDH) begins with a command end marker test. In
Depending on this, is either way out of the procedure or 
continue. 

   The team at 8CD3H in
Register BC is given the initial
printing position (line and
column), in the example
respectively 16H (22) and 1FH
(31), then there is a line appears in the
bottom of the screen. You can
change them (we consider
version of such changes). Then, the procedure call
Print 8D0FH.

   With a double height character
will be especially noticeable when
Scrolling will not occur smoothly - it is immediately
manifested in the form of distortion of vertical lines. 
Therefore, the scrolling occurs in increments in a first pixel 
of the upper half of the symbol (1 familiarity), then 
immediately lower. When you call procedures scrolling - 8CFEH -

pre-register at the address given by the HL system on display 
file corresponding to the top pixel line shifts familiarity (in 
this example is 22-th row and 31-e familiarity). After running 
a couple cycles of scrolling should command HALT, which is 
necessary not only for job speed of ticker, but also

to synchronize the images with
Vertical TV
to eliminate distortions of characters. After that there is a 
loop for printing the next character text message. 

   A few words about the procedure
Print 8D0FH. The team at 8D19H in register DE is given by
address corresponding to the value
CHARS that character set,
which will be printing the text crawl. When
Using downloadable character set must be considered that the 
height of symbols - double, so what is beautiful for a single 
height, can appear distorted when the double

height.

   Authors with the development of a procedure was laid down an 
interesting point: the system is introduced the cell, which 
determines the height of the ticker symbols. It can be double 
or single. Specifies the height of the cell contents 8D64H 
(36,196). If there is zero the height - double. Any non-zero 
value specifies a single height of the symbols. This check

performed at 8D2CH. In
Depending on this happening
performance of different units: in
single height - 8D32H ... 8D3AH, and at the double - 8D3CH ... 
8D4DH. The principal difference these blocks is a single or a 
double appeal to the procedure for transferring 8 bytes on

Screen 8D59H.

   Please note that nowhere
Playing no change in the color attributes of the screen. They 
are "transparent", ie those which were given previously in 
these positions the screen. 


   Now a few words about changing the marquee. Suppose that you 
want, to a running line was located at the top of the screen, 
but to deal with than the entire line, and

only familiarity with the 10 to 21 (ie
there are only 12 familiarity in the middle of the line). To do 
this we just change the position to start printing:

1423.

   8CD3 011500 LD BC, # 0015
2

   In addition, it is necessary in accordance with this change 
addresses in the file system on display for scrolling: 1423.


   8CDC 211540 LD HL, # 4015

   8CE2 213540 LD HL, # 4035

   8CE8 211540 LD HL, # 4015

   8CEE 213540 LD HL, # 4035
2

   It is also necessary to limit
scroll zone 12-familiarity:
1423.

   8D01 060C LD B, # 0C
2

   The number printed at the end of the gaps can now be reduced 
to 11, setting a marker at the end

new location.

   Experience the resulting variant, and we see that for small
the length of the on-screen text, the velocity of its
too big - it became difficult to
read. The speed can be reduced
if the following changes:
1423.

   8CD9 0608 LD B, # 08


   8CE8 2000 NOP

   .... .. ...

   8CF3 2000 NOP
2

   Now a team of HALT will not run after the pair, and after 
each subroutine call scrolling, and the rate of O

Text slowed twice.

   Now everything is in order. It remains only to draw with
ART-STUDIO resulting zone
running line (including the INK and
PAPER those familiarity, which will
output text) in the form of placards or display, which is
part of the spacecraft cabin or otherwise - on a plot of your 
game. 


   Program in BASIC for block codes "running
Line:


   1 READ ram: CLEAR ram: READ f
$: READ st: READ len: FOR a = st T
O st + len-1: READ b: POKE a, b: NE
XT a: SAVE f $ CODE st, len

   2 RANDOMIZE USR st

  1910 DATA 36031, "rt", 36032,268
 100 DATA
033,133,141,205,205,140,033,101,
141,205,205,140,201,203,126,192,
203,254,229,001,031,022,205,015,
141,006,004,197,033,223,080,205
 110 DATA
254,140,033,255,080,205,254,140,
033,223,080,205,254,140,033,255,
080,205,254,140,118,193,016,227,
225,203,190,035,024,207,014,008
 120 DATA
229,006,032,167,203,022,043,016,
251,225,036,013,032,242,201,126,
230,127,229,038,000,111,041,041,
041,017,000,060,025,120,230,248
 130 DATA
198,064,087,120,230,007,015,015,
015,129,095,197,058,100,141,167,
040,010,006,008,126,018,020,035,
016,250,024,020,122,008,205,089
 140 DATA
141,008,087,123,198,032,095,048,
004,122,198,008,087,205,089,141,
193,012,225,203,126,035,192,024,
182,006,004,126,018,020,018,020
 150 DATA
035,016,248,201,000,032,032,032,
032,032,032,032,032,032,032,032,
032,032,032,032,032,032,032,032,
032,032,032,032,032,032,032,032
 160 DATA
032,032,032,032,255,085,078,065,
085,084,072,079,082,073,083,069,
068,032,068,073,083,067,076,079,
083,085,082,069,032,079,070,032
 170 DATA
084,072,073,083,032,073,078,070,
079,082,077,065,084,073,079,078,
032,073,083,032,080,085,078,073,
083,072,065,066,076,069,032,066
 180 DATA
089,032,068,069,065,084,072,032,
033,033,033,255