Doodle

This is a joystick-driven drawing program designed for young children, using the STICK function to read a joystick in port 1. The cursor is rendered as a small cross (two perpendicular lines, four pixels each) drawn with PLOT/DRAW, and the previous cursor position is erased by redrawing it with INVERSE 1 before plotting the new position. Each direction of movement triggers a short BEEP with a distinct pitch and duration, providing audio feedback. The screen is initialised with a solid border of block-graphic characters (█, 704 of them) and INK/PAPER colours are set before drawing begins. Fire on joystick port 2 clears the screen and restarts the draw loop; a note in the introduction explains how to invoke a 2040 printer via BREAK.

---

Program Structure

The program divides into three broad phases:

1. Introduction (lines 1–5): Prints a description and waits for any key via a busy-loop on INKEY$.
2. Initialisation (lines 10–130): Sets colours, fills the screen with block characters to create a border effect, and positions the initial cursor at x=5, y=5 with step size s=4.
3. Main draw loop (lines 210–510): Reads the joystick, moves the cursor, erases the old cross with INVERSE, draws the new cross in a random ink colour, and loops.

Joystick Handling

The program uses the TS2068-specific STICK keyword (rendered as | in zmakebas source) to read an analogue joystick. Port 1 provides direction and port 2 provides the fire button.

STICK(1,1) value	Direction	Δx	Δy	BEEP pitch
4	Left	−s	0	1
5	Down-left	−s	+s	2
6	Up-left	−s	−s	5
2	Up	0	−s	3
10	Up-right	+s	−s	1
1	Down	0	+s	3
9	Down-right	+s	+s	6
8	Right	+s	0	6

Fire on port 2 (STICK(2,1)=1 at line 270) branches to line 10, which reinitialises colours and clears the screen.

Cursor Rendering

The cursor is a small cross drawn from two overlapping lines: a horizontal segment (PLOT x-2,y : DRAW 4,0) and a vertical segment (PLOT x,y-2 : DRAW 0,4). The old position is erased by repeating the same geometry with INVERSE 1 (lines 410–440), which XORs the pixels back to their previous state. This avoids having to repaint the background.

Screen Initialisation

Line 50 prints 704 solid block characters (█, char 143) to fill the entire 22×32 display area. This creates a uniform filled canvas rather than a simple CLS. Because the border is also covered, the joystick coordinates are clamped (lines 310–340) to keep the cursor within x∈[5,250] and y∈[5,170], safely inside the pixel grid.

Colour and Sound

Each new cross is drawn in a randomly chosen ink colour: INK (RND*7)+1 at line 460 selects a value in the range 1–7, excluding black (0), so the mark is always visible against the filled background. Each joystick direction also triggers a BEEP with a short duration (~7–14 ms) and a distinct semitone pitch, giving continuous audio feedback during movement.