Brightness Pixels

/**
 * Brightness Pixels
 * by Daniel Shiffman.
 *
 * This program adjusts the brightness of a part of the image by
 * calculating the distance of each pixel to the mouse.
 */

PImage* img;

void setup() {
  size(640, 360);
  frameRate(30);
  img = loadImage("moon-wide.jpg");
  img->loadPixels();
  // Only need to load the pixels[] array once, because we're only
  // manipulating pixels[] inside draw(), not drawing shapes.
  loadPixels();
}

void draw() {
  for (int x = 0; x < img->width; x++) {
    for (int y = 0; y < img->height; y++) {
      // Calculate the 1D location from a 2D grid
      int loc = x + y * img->width;
      // Get the R,G,B values from image
      float r, g, b;
      r = red(img->pixels[loc]);
      //g = green(img->pixels[loc]);
      //b = blue(img->pixels[loc]);
      // Calculate an amount to change brightness based on proximity to the mouse
      float maxdist = 50; //dist(0,0,width,height);
      float d = dist(x, y, mouseX, mouseY);
      float adjustbrightness = 255 * (maxdist - d) / maxdist;
      r += adjustbrightness;
      //g += adjustbrightness;
      //b += adjustbrightness;
      // Constrain RGB to make sure they are within 0-255 color range
      r = constrain(r, 0, 255);
      //g = constrain(g, 0, 255);
      //b = constrain(b, 0, 255);
      // Make a new color and set pixel in the window
      //color c = color(r, g, b);
      color c = color(r);
      pixels[y * width + x] = c;
    }
  }
  updatePixels();
}