//-----P.121-----
PImage    Simg; //Source image
int inc=0, dec=255, flag=0;

void setup(){
  Simg = loadImage("./img/color.jpg");
  surface.setResizable(true);  //image size window
  surface.setSize(Simg.width, Simg.height);
  imageMode(CENTER);
}
 
void draw(){
  image(Simg, width/2, height/2,width,height );  
  if(flag==0){     // fade-in
    fill(0,0,0,dec);
    rect(0,0,width,height);
    dec--;
    if(dec==0) {
      flag=1;
      dec=255;
    }
  } else {          //fade-out    
    fill(0, 0, 0, inc);
    rect(0,0,width,height);
    inc++;
    if(inc==255) {
      flag=0;
      inc=0;
    }
  }
}