Playboy Bunny

This program prints a Playboy bunny logo as ASCII/block-graphic art on a ZX printer using LPRINT statements. After prompting the user to confirm the printer is on, it enters FAST mode before sending the image to suppress slow screen rendering during output. The bunny silhouette is constructed entirely from ZX81 block graphic characters — particularly the half-block and quarter-block elements (▌, ▖, ▗, ▘, ▝, ▞, ▟, ▙, ▀, ▄, █) — giving diagonal and curved edges despite the low-resolution character grid. The percent signs (%) serve as filled space characters to create a solid background, while the right-hand edge uses the ▌ character as a consistent border. The GOTO 350 branch on a non-“Y” answer skips directly to STOP, safely bypassing all LPRINT output.

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Program Analysis

Program Structure

The program is straightforward and linear, divided into three phases:

1. Introduction (lines 10–40): Displays a title and prompts the user to confirm the printer is ready, accepting a Y/N response into I$.
2. Output (lines 90–340): Enters FAST mode, then sends 23 lines of block-graphic art plus two blank lines to the printer via LPRINT.
3. Termination (line 350): STOP halts execution regardless of the path taken.

Lines 360–370 (SAVE and RUN) are present after the STOP and are never reached during normal execution; they exist as a convenience loader.

Printer Gating

Line 50 tests I$<>"Y" and jumps to GOTO 350 (the STOP line) if the user does not enter exactly “Y”. This means any input other than an uppercase Y — including lowercase “y” — will skip printing entirely. There is no case-normalisation, which could surprise users who type “y”.

FAST Mode Usage

Line 90 invokes FAST before any LPRINT call. On the ZX81/TS1000, FAST disables the display refresh interrupt, allowing the CPU to run at full speed. This significantly accelerates the printing loop since the machine is not sharing CPU time with screen rendering, and avoids the characteristic flicker that would otherwise occur during a lengthy series of LPRINT statements.

Block Graphic Construction

The image is built using ZX81 block graphic characters occupying the standard 2×2 pixel-per-character positions. The escape sequences used and their visual meanings are:

Escape	Glyph	Role in image
\:	▌	Right-hand border column
\.'	▞	Diagonal rising edge
\:.	▙	Filled lower-left curves
\'.	▚	Diagonal falling edge
\'..	(▘▄ pair)	Top and bottom fill transitions
\''	▀	Upper half fill
\..	▄	Lower half fill
\ '	▝	Upper-right quarter
\ .	▗	Lower-right quarter
\:'	▛	Three-quarter fill (upper-left)
\::	█	Full block (solid fill)

The percent character % is used as the background fill — this is simply the literal percent sign character, which on the ZX81 thermal printer renders as a dense stipple approximating a solid dark region, forming the filled silhouette of the bunny against the paper.

Image Layout

The image spans lines 100–320 (21 LPRINT statements carrying graphics, plus two blank lines at 330–340). A consistent \: (▌) character terminates every printed row, acting as a right-margin sentinel. The ears of the bunny are suggested in lines 130–170 by the asymmetric block-graphic curves, while the bow-tie detail appears around lines 200–210 using \..\..\.. sequences.

Notable Techniques

• Use of FAST before printer output to maximise throughput and eliminate screen flicker during a long LPRINT sequence.
• Consistent right-border character (\: = ▌) on every LPRINT line ensures the printed image has a clean right edge regardless of line length variation.
• The guard condition at line 50 uses a strict string inequality, meaning only exact uppercase “Y” proceeds — a minimal but functional input validation.
• The % background fill exploits the density of the percent glyph on thermal paper rather than using a true block graphic, a pragmatic approach to solid-area fill.

Bugs and Anomalies

• The program does not return to SLOW mode after printing. If the user somehow continued execution past line 350, the display would remain in FAST mode. In practice this is harmless since STOP terminates cleanly.
• Case sensitivity on the Y/N prompt (line 50) means lowercase “y” skips printing — a minor usability issue.
• The PRINT AT coordinates in lines 20–30 place text at rows 12 and 18 respectively, which may overlap on a 24-line display but is not harmful.