import processing.opengl.*;

float fadeTime;
boolean fadeIn=false,fadeOut=false,on=false;
color col;

void setup() {
  size(400,400, OPENGL);
  
  col=color(255,150,0, 128);
}

void draw() {
  background(0);
  translate(width/2,height/2);  
  rotateX(radians(frameCount));
  rotateY(radians(frameCount)/3);
  
  if(fadeIn) {
    if(fadeTime<1) fadeTime=fadeTime+1.0/100.0;
    else { // done fading in
      fadeTime=1;
      on=true;
      fadeIn=false;
    }
  }
  if(fadeOut) {
    if(fadeTime>0) fadeTime=fadeTime-1.0/100.0;
    else { // done fading in
      fadeTime=0;
      on=false;
      fadeOut=false;
    }
  }
  
  // fill with the color "col", modifying the
  // alpha by multiplying with fadeTime
  fill(col, alpha(col)*fadeTime);
  
  box(100);
}

void keyPressed() {
  if(key==' ') {
    if(on==false) fadeIn=true;
    else fadeOut=true;
  }
}