/* 6.914, example 0.9

Giving a second or fourth argument for a color - like with fill, stroke, 
or background - will let you change the alpha value (opacity). You can
choose any number between 0 (totally transparent) and 255 (totally opaque.

The default alpha value is 255.
*/


void setup(){
  size(150, 350);
  background(100);
}

void draw(){
  fill(255, 0, 0);
  ellipse(50, 50, 25, 25);

  fill(255, 0, 0);
  ellipse(50, 90, 25, 25);
  fill(255, 0, 0, 255); //same as previous
  ellipse(50, 100, 25, 25);

  fill(255, 0, 0);
  ellipse(50, 140, 25, 25);
  fill(255, 0, 0, 100); // more transparent than previous
  ellipse(50, 150, 25, 25);

  fill(255, 0, 0);
  ellipse(50, 190, 25, 25);
  fill(255, 0, 0, 50); // more transparent than previous
  ellipse(50, 200, 25, 25);
  
  fill(255, 0, 0, 5); //almost totally transparent
  ellipse(50, 250, 25, 25);

  fill(255, 0, 0, 0); //totally transparent
  ellipse(50, 300, 25, 25);
}