Ejemplos 1

A)

void setup() {
  size(480, 120);
}

void draw() {
  if (mousePressed) {
    fill(0);
  } else {
    fill(255);
  }
  ellipse(mouseX, mouseY, 80, 80);
}

 B)

void setup() {
       size(400, 400);
       stroke(255);
     }
    
     void draw() {
       line(150, 25, mouseX, mouseY);
     }
     
     void mousePressed() {
       background(192, 64, 0);
     }
 

C) Alpha transparencia

size(200,200);
background(0);
noStroke();

// No fourth argument means 100% opacity.
fill(0,0,255);
rect(0,0,100,200);

// 255 means 100% opacity.
fill(255,0,0,255);
rect(0,0,200,40);

// 75% opacity.
fill(255,0,0,191);
rect(0,50,200,40);

// 55% opacity.
fill(255,0,0,127);
rect(0,100,200,40);

// 25% opacity.
fill(255,0,0,63);
rect(0,150,200,40);

D)

color c = color(0);
float x = 0;
float y = 100;
float speed = 1;

void setup() {
  size(200,200);
}

void draw() {
  background(255);
  move();
  display();
}

void move() {
  x = x + speed;
  if (x > width) {
    x = 0;
  }
}

void display() {
  fill(c);
  rect(x,y,30,10);
}