Dungeon Generator

This program is an interactive dungeon map generator that draws a grid-based layout on screen and lets the user populate it with rooms, pits, lakes, walls, halls, and doors. It begins by rendering a bordered play area using inverse-video digits and block characters, then iterates through seven predefined room size categories stored in a DIM’d string array R$(7,5), dispatching to GOSUB routines via the computed address VAL “100*Q+2000” to draw rooms of varying dimensions with dot-fill patterns. User-placed features (lakes, walls, halls, doors) are entered as row/column coordinates interactively, with bounds checking, and the completed map can be sent to a printer via the COPY command. The FAST mode is engaged during initialisation to speed up screen rendering.

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Program Analysis

Program Structure

The program divides into several clearly distinct phases:

1. Initialisation (lines 4–78): CLS, FAST, draw the border frame with inverse digits and a blank interior.
2. Room placement (lines 80–220): Define seven room-size categories in R$, prompt the user for counts, and dispatch to subroutines via computed GOSUB.
3. Pit placement (lines 230–290): Scatter inverse-video pit characters at random coordinates.
4. Interactive feature placement (lines 300–500): Four sequential phases for lakes, walls, halls, and doors, each using INPUT for row/column coordinates with bounds checking.
5. Output (lines 1500–1530): Optional COPY to printer, then STOP.
6. Room-drawing subroutines (lines 2100–2760): Seven subroutines, one per room size, each printing dot-filled rectangles at random positions.

Room Size Categories

The array R$(7,5) stores human-readable size labels displayed in the prompt at line 170. The seven entries correspond to subroutines at lines 2100–2700:

Q	R$(Q)	Subroutine	Room footprint
1	20×30	2100	2 rows × 3 cols
2	20×40	2200	2 rows × 5 cols
3	30×50	2300	3 rows × 5 cols
4	40×60	2400	4 rows × 6 cols
5	20×20	2500	2 rows × 2 cols
6	30×30	2600	3 rows × 3 cols
7	40×40	2700	4 rows × 4 cols

Note that the size labels in R$ use inverse-video digit characters (e.g. %2%0%X%3%0), making the dimensions appear highlighted on screen. The actual dot dimensions in the subroutines do not perfectly match the labels — for example, “20×30” yields a 2×3 dot block rather than 20×30 character cells, suggesting the labels are stylistic rather than literal measurements.

Computed GOSUB Dispatch

Line 200 uses GOSUB VAL "100*Q+2000" to dynamically compute the subroutine address from the loop variable Q. This is a well-known space-saving idiom: a single GOSUB replaces seven explicit IF/GOTO branches. For Q=1 through 7, the targets are lines 2100, 2200, …, 2700. Line 2000 contains a bare STOP as a safety guard in case Q is somehow 0, and line 2800 likewise acts as a sentinel past the last valid subroutine.

Border Drawing

Lines 5–78 construct the map border. Line 7 prints a row of inverse-video digits 0–9 repeating across 32 columns as the top border. Lines 10–30 print 20 rows of inverse spaces to fill the play area with a uniform background. Lines 40–76 use a two-pass loop (C=1 TO 2) with an inner loop over A=0 TO 3 (exploiting NOT PI = 0 and LEN STR$ PI = 4) to print characters CHR$(156) through CHR$(159) — block graphic characters — down both the left side (pass 1) and an offset position (pass 2, AT A+10). Line 78 then places an inverse zero at row 20, column 0 to close the frame.

Interactive Placement and Bounds Checking

The lake, wall, hall, and door phases each prompt the user for a row (M) and column (N). Entry of the value 86 for M acts as a sentinel to advance to the next phase (lines 315, 333, 370, 450). Bounds checks vary slightly between phases — for example, walls allow rows 1–20 and columns 1–30, while halls allow rows 1–20 and columns 1–31. A bounds violation silently re-presents the prompt rather than reporting an error.

There is a minor anomaly in the door-placement phase: a bounds violation at line 470 jumps to GOTO 350 (the hall prompt) rather than back to the door prompt at line 430. This means an out-of-range door entry accidentally drops the user into hall-placement mode instead of retrying the door prompt.

Key BASIC Idioms

• SGN PI evaluates to 1 (since PI > 0), used wherever the literal 1 would otherwise appear — saves one byte per occurrence.
• NOT PI evaluates to 0, used for column 0 in PRINT AT statements.
• LEN STR$ PI evaluates to 4 (length of “3.14159…” truncated to display form), used as the upper bound of the border character loop.
• VAL "number" in numeric contexts is a standard token-saving technique on this platform.
• FAST mode at line 5 suppresses the display refresh interrupt during the initial screen draw to speed up rendering.

Unused / Dead Code

Lines 2800–2830 are unreachable during normal execution. Line 2810 contains a CLEAR and line 2820 a SAVE with an inverse-video filename, which appear to be remnants of a development save-and-autorun stub that was never removed from the listing.

Pit Symbol

Line 280 prints "%X" — a single inverse-video X character — to mark pit locations. The prompt at line 230 also displays this character inline to illustrate the symbol to the user.