in which I load an image into my sketch

popcornMask.pde

/*
loading an image into my processing sketch
 */

PImage popcorn;
color yellow = color(255, 255, 0);
int radius;

void setup() {
  size(480, 320);
  radius = 50;
  popcorn = loadImage("DSC_0199.JPG");
  image(popcorn, 0, 0, 600, 400);
}

void draw() {
  image(popcorn, 0, 0, 600, 400);
  mask();
  fill(yellow);
  text("you can click to lift the mask!",mouseX,mouseY+2*radius);
}

void mousePressed() {
  // lifts the mask
  image(popcorn, 0, 0, 600, 400);
  noLoop();
}

void mouseReleased() {
  loop();
}

void mask() {
  // create mask except where mouse is
  loadPixels();
  // square of sidelength 2*radius centered around mouse
  for (int i = 0; i < width; i++) {
    for (int j = 0; j < height; j++) {
      if ((i < mouseX-radius || i > mouseX+radius) || (j < mouseY-radius || j > mouseY+radius)) {
        pixels[j*width+i] = color(0);
      }
    }
  }
  updatePixels();
}