Alpha Mask

/**
 * Alpha Mask. 
 * 
 * Loads a "mask" for an image to specify the transparency 
 * in different parts of the image. The two images are blended
 * together using the mask() method of PImage. 
 */

PImage* img;
PImage* imgMask;

void setup() {
    size(640, 360);

    img = loadImage("moonwalk.jpg");
    imgMask = loadImage("mask.jpg");

    img->mask(*imgMask);   // dereference because mask takes const PImage&

    imageMode(CENTER);
}

void draw() {
    background(0, 102, 153);

    image(img, width / 2, height / 2);
    image(img, mouseX, mouseY);
}