Crasher by Ted Szczypiorski
For Atari BASIC

Crasher is written in standard Atari 
BASIC. It utilizes custom characters to 
make the star field appear to scroll 
horizontally. It also uses 
Player/Missile graphics and technique 
to "print" the shapes to make them move 
a little smoother. It also uses a 
custom Display List.

Line 0:
Sets up protected memory for the custom 
character set and P/M graphics and sets 
variables for where they begin.
Displays WAIT message

Line 1:
sets up string variable storage. B$ has 
five spaces - used for erasing PM 
graphics. For loop is used to (a) copy 
character set; (b) clear some 
characters; (c) set up custom Display 
List.

Line 2:
Initializes A$, which stores the star 
field (a sequential string of 
characters). Clears the screen and 
switches to new character set. Sets 
up initial game play variables.

Line 3:
Pokes used to set up PM graphics. 
Initializes P$, which stores the ship 
data for the ship shapes (every 5 
characters is a different ship 
direction). Sets more variables.

Line 4:
This line resets the game variables 
(score, time, etc.). Changes screen 
color. Displays PRESS FIRE. Loops 
until button is pressed. Clears the 
top two lines (leaves stars in 
place). Resets screen to black.

Line 5:
This line resets the enemy ship. 
Changes sets new direction and x/y 
start.

Line 6:
This is the start of the game play 
loop. Decrements the timer. Displays 
time and score. Reads joystick and 
sets variables depending on joystick 
to move enemy ship accordingly.

Line 7:
Continues setting enemy ship 
variables. Determines direction of 
your ship. Updates character set for 
horizontal star scroll. Determines 
where a new line of stars (if any) 
should go for a vertical scroll.

Line 8:
Inserts or deletes a blank line for 
stars. Figures out string placement 
of enemy ship shape. Sets screen to 
Player 1 position and "prints" enemy 
ship with blanks above and below. 
Sets Screen to Player 0 position.

Line 9:
Prints player ship. Sets screen to 
actual screen. Sets random number 
used for stars and/or new ship. 
Prints new line of characters for 
stars, if need be. Updates counter 
for initial stars. Determines where 
to loop to: Line 6 for regular game 
loop. Line 5 for a new enemy ship. 
Line 4 for a new game. Line 7 for 
initial stars.