Here is a good example of
how fast TURBO BASIC can handle players with an unusual effect which
could be used in your own programs. You are confronted with a blank
screen on which is written an invisible message. As the characters
are the same colour as the background you cannot see them. A player
missile is used as the 'magic window' to reveal the message. One
possible use for this effect would be to create an invisible maze
and then use a joystick to move the window in order to find your way
round the maze but there must be several other applications.
HOW IT WORKS
Two players are used.
Player 0 is used as a frame while Player 2 is used to create the
magic glass. Both players are stored in PM$. I should point out that
line 10 must be typed in first to ensure that PM$ is the first name
in variable name table otherwise the program will not work.
By moving the data within
PM$, the players are moved vertically quite fast, so fast in fact
that the players are moved from the bottom to the top of the screen
instantly. PM graphics are set up in PROC SETUP at line 340. Here is
where PM$ is re-directed to the PM storage area. Turbo Basic
automatically clears arrays and strings when DIMed but in this
instance we need PM$ to be filled with hearts. Line 390 is a quick
fill routine which can be used to fill any string with any
character. B$ is the shape of the window while C$ is the frame.
There are a few examples
included of the special features of Turbo Basic which I will mention
in this brief run-down of the program. The dashes in line 100 are
obtained just by typing 2 dashes only, when listed you will find all
30 dashes shown. One thing to note, if you want to put in your own
message, is that there is a semi colon at the end of each print
statement.
Lines 110 to 280 are an
infinite loop. The IF statements on lines 180 and 200 are NOT
followed by a THEN. Make sure you type the colons where you would
expect THEN to occur. The only jump out of this loop appears on line
160. By pressing START, SELECT, or OPTION, the program goes to PROC
SLOW on line 300.
The SOUND statement with
no parameters turns off all sound. PAUSE is a quick way of producing
a delay instead of using a FOR/NEXT loop.
NOW FOR THE MAGIC!
The 'magic' is performed
in line 430 where the PRIORITY register is set so that the playfield
(in this case capital letters) has priority over Player 2. So there
the secret is out! What really happens is that wherever Player 2 is
on the screen, the Player only covers the background and not the
text thus framing each character.
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YOU CAN DO THIS
So there's another
example of Turbo programming. Can you do better? We'll pay you £20
for a good example of Turbo programming. It must use the features
unique to Turbo and be well structured and it must fit on one page.
Please also include a brief explanation of the program. Anything
will do, but try and make it something that uses the unique features
of Turbo Basic.
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WHAT IS TURBO BASIC?
Turbo Basic is
a new Basic language for the Atari originally published in
the German magazine Happy Computing who retain the copyright
but have released the program to the public domain. It adds
over 60 new commands to Atari Basic, runs three to five
times as fast, is totally compatible with Atari Basic and
comes with a compiler to compile any Atari BAsic or Turbo
Basic program to run at machine language speed. You should
be able to get a copy from any source of Public Domain
software such as your local user group or the PAGE 6
Accessory Shop.
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