Ford Falcon

This program renders a detailed pixel-art falcon graphic on screen using ZX Spectrum block graphics characters, building the image line by line with timed delays between drawing steps to create an animated reveal effect. The main graphic is assembled using a combination of block graphics (▖, ▘, ▀, ▌, █, etc.) and inverse-video characters to form the bird’s body, wings, and talons. Two delay subroutines at lines 2000 and 3000 provide coarse timing — 30-iteration and 10-iteration busy loops respectively — controlling the pace of each drawing step. An introductory animation at line 5000 simulates a diving or landing effect by printing and erasing dots in a V-shaped spreading pattern before the main bird is drawn.

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Program Analysis

Program Structure

The program divides into four logical sections:

1. Lines 0–10: REM headers crediting the author and naming the piece.
2. Lines 15–540: Main drawing routine — calls the intro subroutine, then draws the falcon body, wings, talons, and labels sequentially, interspersed with delay calls.
3. Lines 2000–3020: Two timing subroutines — a slow delay (FOR P=1 TO 30) and a fast delay (FOR P=1 TO 10).
4. Lines 5000–5170: Intro animation subroutine, followed by dead code (STOP, CLEAR, SAVE, RUN) that is never reached in normal execution.

Intro Animation (Lines 5000–5130)

The subroutine at line 5000 animates a simple diving/approach effect before the bird is drawn. It first prints a * at column 19, then steps down rows 0–4 printing and immediately erasing a . at the same column, giving a flicker. From rows 5 to 12 it symmetrically expands outward: dots are printed one column to the left (T-1) and one to the right (V+1) of centre, then immediately erased, widening a V-shape on each row. This simulates a bird approaching from a distance.

Block Graphics Usage

The artwork makes heavy use of ZX Spectrum block graphic escape sequences. The main body text of the falcon is rendered with combinations of these characters:

• \## — full block █
• \~~ / \,, — various quarter-block characters used for diagonal edges
• \:., \::, \.., \.: — additional block graphics for shading and body contour
• \;; — inverse space / solid block variant used for fill
• % — space character used for spacing/clearing within PRINT strings

The wing sweep (lines 150–180) is drawn programmatically: a FOR G=16 TO 7 STEP -1 loop prints \:. (▙) diagonally upward-left, with F incrementing each iteration to step one row down per column — tracing the swept leading edge of a wing.

Delay Subroutines

Two busy-wait subroutines control drawing pace:

Subroutine	Loop count	Relative delay	Usage
GOSUB 2000	30	Longer pause	Between major body sections
GOSUB 3000	10	Shorter pause	Between fine detail strokes

Both subroutines share the loop variable P, which causes no conflict since they are never nested.

Inverse Video Text

Several labels are printed using the %X inverse-video escape: %F, %O, %R, %D spell “FORD” in inverse video at lines 480–510, and %A%W/83 at line 530 signs the artwork “AW/83” (Anthony Willing, 1983) in inverse characters at the bottom-right of the screen.

POKE to Display RAM

Line 540 executes POKE 16384,74. Address 16384 is the very first byte of the display file. Writing 74 (binary 01001010) sets specific pixels in the top-left character cell of the screen — a small finishing touch or signature pixel tweak applied after the drawing is complete.

Dead Code (Lines 5140–5170)

Following the RETURN at line 5130, lines 5140–5170 contain STOP, CLEAR, SAVE "1019%6", and RUN. These are unreachable in normal program flow and represent leftover development/save scaffolding. The SAVE filename encodes %6 as an inverse-video digit.

Notable Techniques

• Programmatic diagonal line drawing with paired loop variables (F and G) for both the wing sweep and the expanding intro V-shape.
• Immediate erase-after-draw within the same loop iteration in the intro animation (PRINT AT … "." … PRINT AT … " "), achieving animation without screen clearing.
• All timing done with FOR/NEXT busy loops — no PAUSE statement used.
• The horizontal ground line (lines 200–230) is drawn with a FOR Z=6 TO 29 loop plus a final out-of-loop print at column 30, suggesting the loop boundary was adjusted but the extra cell added manually.