Starfield Trail (Apple II) by Toolkitman

MATTEO TREVISAN TOOLKITMAN STARFIELD APPLE IIE

STARFIELD : Matteo Trevisan : Free Download, Borrow, and Streaming : Internet Archive

1HGR:DIMX(19),Y(19),Z(19):C=140:D=96
2FORI=0TO19:X(I)=RND(1)*280:Y(I)=RND(1)*192:Z(I)=RND(1)*8+2:NEXT
3HCOLOR=3
4FORI=0TO19
5IFX(I)<0ORX(I)>279ORY(I)<0ORY(I)>191THENX(I)=RND(1)*280:Y(I)=RND(1)*192:Z(I)=RND(1)*8+2:GOTO9
6HPLOTX(I),Y(I)
7X(I)=X(I)+(X(I)-C)/Z(I)
8Y(I)=Y(I)+(Y(I)-D)/Z(I)
9Z(I)=Z(I)-.1:IFZ(I)<=0THENX(I)=RND(1)*280:Y(I)=RND(1)*192:Z(I)=RND(1)*8+2
10NEXT:GOTO4

STARFIELD TRAIL — Jury Presentation (English)

Title

STARFIELD TRAIL – PUR‑80

Platform

Apple IIe — AppleSoft BASIC

Category

PUR‑80 [moved to category SCHAU, because it isn't a game, the organizer]

Short Description

A 20‑star perspective starfield rendered in high‑resolution graphics.

Stars accelerate outward from the screen center using a lightweight projection formula.

The screen is never cleared, producing a smooth, natural trailing effect reminiscent of early demo‑scene aesthetics.

All ten lines comply with the PUR‑80 80‑character limit.

Technical Summary

Uses DIM to enable 20‑element arrays while staying within PUR‑80 constraints.

Implements a minimalist projection model to simulate depth and outward motion.

Avoids screen clearing to create a motion‑trail effect without extra computation.

Includes coordinate validation to prevent out‑of‑range HPLOT calls.

Reinitializes stars with compact RND expressions to maintain density and flow.

Designed for real Apple IIe hardware, balancing star count and performance.

Line‑by‑Line Explanation (English)

Line 1

HGR:DIMX(19),Y(19),Z(19):C=140:D=96  

Enters high‑resolution graphics mode.

Allocates three arrays (X, Y, Z) with 20 elements each.

Defines the screen center (C, D), used for perspective expansion.

Line 2

Initializes all 20 stars with random X and Y positions and a depth Z between 2 and 10.

This creates a scattered starfield ready for animation.

Line 3

Sets the drawing color to white.

The program is intentionally monochrome to match classic Apple II demo aesthetics.

Line 4

Begins the main animation loop, iterating through all 20 stars.

Line 5

Checks whether a star has moved outside the valid screen area.

If so, it is immediately reinitialized with new random coordinates and depth, ensuring continuity and preventing HPLOT errors.

Line 6

Plots the star at its current position.

Because the screen is never cleared, each plotted point contributes to the trailing effect.

Line 7

Updates the X coordinate using a simple projection formula:

the farther a star is from the center, the faster it moves outward.

Line 8

Same projection update as line 7, but applied to the Y coordinate.

Line 9

Reduces the depth Z to simulate forward motion.

If Z reaches zero, the star is reinitialized to maintain density and flow.

Line 10

Ends the loop and jumps back to line 4, creating a continuous animation cycle.