Joystick

This program moves a copyright symbol (©) around the screen using a joystick, reading STICK values to detect directional input. The cursor position is tracked in variables A (row) and B (column), with boundary clamping applied to keep within the 22-row by 32-column display area. Each iteration redraws the character with a randomly chosen INK color (0–6) via `INT(RND*7)`. A second joystick trigger (STICK 2) allows the displayed character to be changed to a random printable character in the range CHR$(91)–CHR$(143).

Program Structure

The program is a short main loop that reads joystick input and repositions a character on the screen. Initialization at lines 10–20 sets the row (A), column (B), and display character (Z$) to their starting values. Lines 30–80 form the core loop: print, then test each directional STICK value and update position accordingly. Line 90 handles a fire/button event on a second joystick port to randomize the character. Line 100 jumps back to line 30 unconditionally.

STICK Value Decoding

The STICK(1,2) call returns a bitmask representing the joystick directions. The values tested correspond to the following directional combinations:

Each directional line (50–80) tests three STICK values: the cardinal direction and two diagonals that include that component. This correctly handles diagonal joystick movement by updating both axes independently across consecutive IF checks.

Boundary Clamping

After each position update, the new value is checked against the display limits: row A is clamped to 0–21 and column B to 0–31, matching the 22×32 character grid. When a boundary is hit, the value is reset to the limit and execution jumps directly to line 30 via GO TO 30, skipping the remaining directional checks for that frame.

Display Technique

Line 30 prints Z$ at position (A,B) with a randomly selected INK color on every iteration. Because there is no PRINT AT to erase the previous position, the character trail remains on screen, progressively painting the display as the symbol moves. The FLASH 0 at line 40 ensures flashing is suppressed each cycle, though it has no functional effect unless FLASH was previously set.

Character Randomization

Line 90 reads a second joystick port via STICK(2,2) and, when value 1 is detected, replaces Z$ with a random character using CHR$(INT(RND*53)+91). This generates characters in the range CHR$(91) to CHR$(143), which spans symbols, lowercase letters, and the lower block graphics characters.

Notable Anomalies

• Line 50 checks STICK(1,2)=5 (Up+Left) for the Up handler, and line 60 also checks STICK(1,2)=5 for the Left handler. When the joystick is at Up+Left (value 5), both A and B are decremented correctly because each IF is evaluated independently.
• The display is never cleared between frames, so the moving character leaves a colored trail across the screen rather than appearing to move cleanly.
• The initial value of Z$ is set to the © character (the zmakebas \* escape), which is a block graphic rather than a printable ASCII symbol.

  10 LET A=0:LET B=A
  20 LET Z$="\*"
  30 PRINT AT A,B; INK INT (RND*7);Z$
  40 FLASH 0
  50 IF STICK (1,2)=1 OR STICK (1,2)=5 OR STICK (1,2)=9 THEN LET A=A-1:IF A<0 THEN LET A=0:GO TO 30
  60 IF STICK (1,2)=4 OR STICK (1,2)=6 OR STICK (1,2)=5 THEN LET B=B-1:IF B<0 THEN LET B=0:GO TO 30
  70 IF STICK (1,2)=2 OR STICK (1,2)=10 OR STICK (1,2)=6 THEN LET A=A+1:IF A>21 THEN LET A=21:GO TO 30
  80 IF STICK (1,2)=8 OR STICK (1,2)=10 OR STICK (1,2)=9 THEN LET B=B+1:IF B>31 THEN LET B=31:GO TO 30
  90 IF STICK (2,2)=1 THEN LET Z$= CHR$ (INT (RND*53)+91)
 100 GO TO 30