Loadstar 207/207.d81/t.tricks ii

Text File | 2022-08-26 | 7KB | 273 lines

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    J O H N N Y ' S    T R I C K S

    by John "The Mad Gamer" Harris


    Now that I've encountered FAME AND
FORTUNE as well as BIG BUCKS
submitting programs to LOADSTAR,
everyday-people-on-the-street are
stopping me and telling me: 'You need
a shave.' So I remind them of a few
things. Like that I, John William
Harris, am the VERY SAME JOHNNY WHO
WROTE JOHNNY'S TRICKS!!! And the
person, now understanding perfectly,
calls the local Facility for the
Mentally Disturbed. So I guess I'll
have to submit another program before
they come haul me away.

    This is a series of machine
language routines designed for use in
your own programs. In most cases, a
quick SYS and a few parameters are all
that it will take, and people will
soon be stopping YOU on the street and
telling YOU to shave.

    To use "tricks.o" in your BASIC
program, just load the ML into place
at $C000 (49152) with this line:

  sys57812"tricks.o",dv,0:poke780,0
  poke781,0:poke782,192:sys65493

 and all of the following tricks are
at your disposal. Here are directions
for each trick:


 [COPYROM]
  Address:49152
  Format:SYS 49152,CSS
  (CSS stands for Character Set
    Start.)

 What it does: Puts a copy of the ROM
set starting at the address you
specify. So, to copy the ROM set to
34816, the character set location used
in the demo, just enter
SYS49152,34816.


 [CLEARSET & RSTORSET]
  Addresses:49251 and 49277
  Format:SYS49251,CSS
         SYS49277,CSS

 By directly altering character
memory, this makes it appear that all
the characters on the screen are
sliding off. RSTORSET does the
opposite, making them slide back on.
To use RSTORSET, you've got to use
REMBRSET first. (see below)


 [FADEOUT & FADEIN]
  Addresses:49442 and 49477
  Format:SYS49442,CSS,speed
         SYS49477,CSS,speed

 Remember that nifty MIST routine that
LOADSTAR's title screen used to use?
This is a version for custom character
sets. FADEOUT fades the set out, and
FADEIN does the opposite. To use
FADEIN, you've got to use REMBRSET
first.


 [RVRSESET]
  Address:49674
  Format:SYS49674,CSS

 Simply reverses the set specified,
turning it into a photographic
negative of itself.


 [XORSET]
  Address:49722
  Format:SYS49722,CSS,number to be
    XORed

 Exclusive-ORs every byte in every
character by the number you give.
Thus, it's a little bit technical by
definition. See the demo program for
a few ways you can use it.


*SCRWEDGE
  Address:49778
  Format:SYS49778,start in memory of
   the character in question,direction

 Think back to Jon Mattson's MAZE
CHASE, published many centuries ago.
Remember how you stared at that title
screen, with it's moving grid
background? While I'm not sure, I
think this was how it was done. It
wedges into the interrupt routine, and
directly changes the graphics
information for one character, whose
start address you specify.

 This might not seem like much, but if
you fill the whole screen with this
character, like in the title screen
for MAZE CHASE, it looks like the
screen is scrolling without having to
resort to any messy smooth scrolling
routines. If you are using sprites,
this is all you need to create an
illusion of motion. The value for the
'direction' in the SYS statement works
out like this:

  1-scroll down
  2-scroll up
  4-scroll right
  8 scroll left

 If you want to combine two
directions, OR them together. (Up and
left would be 2 OR 8, or 10.)

 Also, there are two additional
features to this routine. By ORing
the direction number by 16, you
activate joystick mode. With this,
when you push the joystick in port #2
in a direction, the character will
scroll in the OPPOSITE direction, so
if you have, say, a spaceship on the
screen, it looks like the ground,
stars, etc. are passing by below you.
If you provide sprites moving in the
same direction, this effect might
prove helpful in games.

 If you OR the direction number with
32, you activate flash mode, in which
the wedge not only scrolls the
character, but reverses it too. Since
it does this every time the interrupt
comes around, it looks like the
screen's flashing. Great for
explosions.


 [WEDGEOFF]
  Address:50009
  Format:SYS50009

 Turns off the wedge. (see above)


 [SPREDSET]
  Address:50022
  Format:SYS50022,CSS

 Widens stuff. It puts a pixel to the
left and to the right of every pixel
already on the screen every time you
call it.


[RUBSET]
  Address:50084
  Format:SYS50084,CSS

 I admit it, I couldn't think of a
good name for this one. It sort of
'tears' everything apart. Most
effective on a screen with a lot of
reversed characters.


 [RTRVESET and REMBRSET]
  Addresses:50276 and 50301
  Format:SYS50276,CSS
         SYS50301,CSS

 Calling REMBRSET stores a copy of the
set starting at the location you gave
it in a 'buffer' starting at 51200.
Routines that require a set to
operate, like FADEIN and RSTORSET get
the{SHIFT-*}information from here. Here's an
example of how you use it.

  SYS REMBRSET,S1
  SYS FADEOUT,S1
  SYS R1,102
  SYS FADEIN,S1

 Assuming the VIC-II chip is expecting
character information at S1, SYS
REMBRSET,S1 stores a copy of the set
in the buffer. SYS FADEOUT,S1 fades
the screen to black, providing an
eye-catching effect but destroying the
current character set in the process.
SYS R1,102 fills the screen with
character 102 (the checkerboard
pattern), and SYS FADEIN,S1 copies the
stored character set from the buffer
back into the current character set,
one pixel at a time. Please note the
SYS R1,102 command isn't nessesary.


 [SCREEN FILL]
  Address:50171
  Format:SYS50171,character number

 Fill the current screen, based on
location 648, with the character you
tell it to.


 [COLOR FILL]
  Address:50224
  Format:SYS50224,color number

 Puts the color you want in color
memory (55296).



     Well, that's it. Of course, all
of these things are demonstrated in
the Demo program. You can either
select something from the menu, or
push a number key for a 'quickie'
example. Another new feature is a
display that shows the command syntax
for each routine.

    And don't forget you don't really
need a custom set for this program.
You can simply copy the ROM set to a
free area of memory, set the VIC-II
registers to get the character info
from there, and off you go. But if
you do use a custom character set, to
make sure nothing happens to it, load
it into an unused area of memory and
then copy it into place by
REMBRSETing it and RETRVESETing it to
the place VIC-II needs it. That way,
if for some reason you destroy the
copy, you don't have to reload it.
Just make another copy.

 JH-TMG