int WIDTH = 400;
int HEIGHT = 300;
int GRIDSIZE = 4;
int POINTNUM = 8000;

Gridpoint[] g = new Gridpoint[POINTNUM];

class Gridpoint {
	int dir;
	float vel;
	float x, y;
	
	Gridpoint(int xIn, int yIn, int dirIn, float velIn) {
		x = xIn;
		y = yIn;
		dir = dirIn;
		vel = velIn;
		}
	
	void update() {
		if(dir == 1) {
			y += vel;
			
			if(y < 0)
				y += HEIGHT;
			else if(y > HEIGHT)
				y -= HEIGHT;
			}
		else {
			x += vel;
			
			if(x < 0)
				x += WIDTH;
			else if(x > WIDTH)
				x -= WIDTH;
			}
		rect(x,y,vel*5,vel*5);
		}
	}

void setup() {
	size(400,300);
	background(#ffffff);
	noBackground();
	stroke(#AAAAAA);
	for(int i = 0; i < POINTNUM; i++) {
		int x = (int)random((WIDTH)/GRIDSIZE)*GRIDSIZE;
		int y = (int)random((HEIGHT)/GRIDSIZE)*GRIDSIZE;
		int dir = (int)random(2);
		float vel = random(-2,2);
		g[i] = new Gridpoint(x,y,dir,vel);
		}
	}

void loop() {
	for(int i = 0; i < POINTNUM; i++) {
		g[i].update();
		}
	}