int x1 = 0;
int y1 = 0;

int x2 = 0;

int y2 = 0;

int xspeed1 = 3;
int yspeed1 = 4;

int xspeed2 = 4;
int yspeed2 = 3;

int size = 50;

void setup() {
size(640, 480);

x1 = int(random(width));
x2 = int(random(width));

y1 = int(random(height));
y2 = int(random(height));

}

void draw() {

background(0);
stroke(0);
fill(255, 255, 0);
if(frameCount % 20 < 10) {
arc(x1, y1, size, size, 0.52, 5.76);
} else {
arc(x1, y1, size, size, 0.1, 6.18);
}

if(frameCount % 20 < 10) {
arc(x2, y2, size, size, 0.52, 5.76);
} else {
arc(x2, y2, size, size, 0.1, 6.18);
}

x1 = x1 + xspeed1;
y1 = y1 + yspeed1;

x2 = x2 + xspeed2;
y2 = y2 + yspeed2;
if(x1 < 0 || x1 > 640) {
xspeed1 = -xspeed1;
}

if(y1 < 0 || y1 > 480) {
yspeed1 = -yspeed1;
}

if(x2 < 0 || x2 > 640) {
xspeed2 = -xspeed2;
}

if(y2 < 0 || y2 > 480) {
yspeed2 = -yspeed2;
}

}