snake.pde

int width = 500;
int height = 200;
int lineWidth = 10;
int lineLength = 1000;

int startX = 0;
int startY = 0;

Snake snake;

void setup() {
    frameRate(60);
    size(width, height);
    snake = new Snake(startX, startY, lineLength);
}

void draw() {
    background(0,0);
    strokeWeight(lineWidth);
    snake.render();
    snake.update();
}

class Snake {
    ArrayList points;
    Point start;
    int length;

    public Snake(x, y, l){
        points = new ArrayList();
        length = l;
        start = new Point(x, y);
        updateListPoints();
    }

    void render(){
        stroke(0, 0, 255);
        Point o;
        for (Point p : points) {
            if(o != null)
                line(o.x, o.y, p.x, p.y);
            o = p;
        }

        stroke(255, 0, 0);
        point(start.x, start.y);
    }

    void update(){
        start = getNextStart();
        updateListPoints();
    }

    private Point getNextStart() {
        if(start.y == 0){
            if(start.x < width) start.x++;
            else start.y++;
        }
        if(start.x == width){
            if(start.y < height) start.y++;
            else start.x--;
        }
        if(start.y == height){
            if(start.x > 0) start.x--;
            else start.y--;
        }
        if(start.x == 0){
            if(start.y > 0) start.y--;
            else start.x++;
        }
        return start;
    }

    private void updateListPoints() {
        int t = length;
        points.clear();
        points.add(start);
        Point old = start;
        while (t > 0) {
            if(old.y == 0 && old.x != 0){
                if(t < old.x){
                    points.add(new Point(old.x - t, 0));
                    t = 0;
                }
                else {
                    t -= old.x;
                    old = new Point(0, 0);
                    points.add(old);
                }
            }
            else if(old.x == width){
                if(t < old.y){
                    points.add(new Point(width, old.y - t));
                    t = 0;
                }else{
                    t -= old.y;
                    old = new Point(width, 0);
                    points.add(old);
                }
            }
            else if(old.y == height){
                if(t < width - old.x){
                    points.add(new Point(old.x + t, height));
                    t = 0;
                }
                else{
                    t -= (width - old.x);
                    old = new Point(width, height);
                    points.add(old);
                }
            }
            else if(old.x == 0){
                if(t < height - old.y){
                    points.add(new Point(0, old.y + t));
                    t = 0;
                }
                else {
                    t -= height - old.y;
                    old = new Point(0, height);
                    points.add(old);
                }
            }
        }

        return points;
    }
}

class Point {
    int x,y;
    Point(int x_, int y_) {
        x = x_;
        y = y_;
    }
}