RomeoT

This program implements a carnival-style weight-guessing game where the player enters their weight and a “guesser” character attempts to predict it. Custom UDGs (User Defined Graphics) are defined via DATA statements and POKEd into memory at USR “\a” through USR “\e”, creating the character sprites and display elements. The game draws a scale using block graphics and PLOT/DRAW commands, animates a weight indicator moving up or down, and compares the player’s input against a randomly generated target range. Lines 9900–9952 contain an elaborate self-listing routine that reads the program’s own tokenized BASIC from memory, decodes keyword tokens, and renders each statement graphically using DRAW commands to approximate letter shapes, with arc-based curves for rounded characters like O, C, and S.

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Program Analysis

Program Structure

The program divides cleanly into two independent sections. Lines 10–370 implement the weight-guessing game itself. Lines 9900–9952 form a standalone self-listing and pseudo-pretty-printer routine that is never called by the game — it must be invoked separately (e.g., by RUNning from line 9900 or via the SAVE line’s LINE 0 autostart).

UDG Initialization

Lines 20–70 define five custom UDGs (\a through \e, characters 144–148) using 40 bytes of DATA. Each UDG is 8 bytes tall. The DATA at line 30 uses the variable a as a placeholder (value 0 after being consumed by READ) — this is a subtle trick where a appears in the DATA list itself, producing whatever value a currently holds at read time, which is 0 after the first READ iteration resets it. The POKE loop at line 70 writes sequentially to USR "\a" through USR "\a"+39, filling five UDGs.

Game Logic

The game flow is as follows:

1. Draw a decorative border using block graphics (lines 80–110).
2. Initialize player position (x=21, y=8) and draw a scale with PLOT/DRAW (line 120).
3. Place the player sprite (\a) at the starting position (line 130).
4. Pick a random target row h in the range 8–18 and display a marker (\b) (lines 140–150).
5. Prompt for and validate weight input w, 1–14 (lines 160–170).
6. Animate a weight dropping (line 180) and redraw the scale line (line 190).
7. Move the sprite upward by w rows (lines 200–230) then shift left two columns (line 240).
8. Compare final position against target h: exact match triggers a win (lines 280–310); landing above the target causes a fall animation (lines 320–350); landing below shows a failure sprite (\e) with a low BEEP (line 270).

Graphics Techniques

The playing field border is drawn entirely with block graphic characters printed via PRINT AT, using INK 6 (yellow) for the frame and INK 4 (green) for interior details. The weighing scale is rendered with PLOT 64,0: DRAW 37,16 and later erased and redrawn with DRAW OVER 1 to show the scale tipping. Sprite animation uses character-cell movement: the old position is blanked with a space and the new position is printed with the UDG character.

Self-Listing Routine (Lines 9900–9952)

This is the most technically ambitious section of the program. It walks the tokenized BASIC program area in memory, decoding each line and rendering keyword tokens as pixel-drawn letterforms using DRAW commands.

• PEEK 23635 + 256*PEEK 23636 (line 9901) reads system variable PROG to find the start of the BASIC area.
• Line 9903 reads the two-byte line number and advances the pointer past the line-length word (4 bytes total header).
• Lines 9906–9911 dispatch on the token byte b to select a drawing subroutine for that keyword’s shape. Token values in the 226–254 range correspond to BASIC keywords.
• Line 9911 draws a generic rectangular letter outline using a sequence of DRAW commands (baseline rectangle with a gap), representing the keyword.
• Line 9923 draws rounded-end forms (for tokens like ON ERR, PRINT, etc.) using arc DRAW calls with -PI angle parameter for semicircles.
• Line 9924 draws plain rectangular outlines for another token class.
• Lines 9925–9932 handle tokens for SOUND (b=250) and STICK (b=243) with a distinctive stepped shape.
• Lines 9933–9938 handle CIRCLE and related tokens, drawing an actual circle with CIRCLE x,y-4,4.
• Lines 9916–9920 scan forward through the token stream byte by byte; byte 34 (") triggers a subroutine to skip string literals (lines 9951–9952), byte 14 skips the 5-byte floating-point number format (LET a=a+4), byte 13 is a newline (end of statement), and byte 58 (:) marks a statement separator handled at line 9939.
• Line 9942 displays a prompt using INVERSE 1, and lines 9943–9945 poll INKEY$ for “v” (view) or “p” (print via COPY).

Notable Idioms and Techniques

• VAL "number" is not used here; GO TO targets are plain literals.
• The DRAW OVER 1 at line 190 erases the previous scale line by XOR-drawing over it, a standard technique for flicker-free animation.
• The self-lister limits output to 20 items (c=20 checks at lines 9921 and 9939) to avoid scrolling off-screen.
• The SAVE line at 9953 uses LINE 0, targeting non-existent line 0, which is a recognized technique to influence program startup behavior.
• The DATA values in line 30 use the variable a literally inside a DATA statement — this is unusual and works because the variable a holds 0 after the first READ, making those entries effectively 0.

Potential Bugs and Anomalies

• Line 30’s use of a in DATA is unconventional. In standard Spectrum BASIC, DATA elements are stored as literals at program entry time, not evaluated dynamically, so a here is the numeric variable’s current value when READ is executed — this works only because a is reliably 0 at that point, but it is fragile.
• The self-lister at line 9946 resets c=0, x=130, y=175 for a fresh render pass, but a continues from wherever the previous pass left off, meaning the “view” mode may not restart from the beginning of the program.
• Line 9950 issues COPY for printer output but does not reset the display mode, so the printed output depends on what is currently on screen.

Token Dispatch Table

Token byte(s)	Description	Drawing routine
226, 234, 242, 254	Rounded-end keyword group	Line 9923 (arc DRAW)
228–230, 232, 235, 241, 247, 249, 253	Rectangular keyword group	Line 9924 (box DRAW)
243, 250	STICK / SOUND	Line 9925 (stepped shape)
236, 237	CIRCLE-related	Line 9933 (CIRCLE + line)
all others	Generic keywords	Line 9911 (default outline)