/*
 * @name Histogram
 * @description Calculates the histogram of an image. 
 * A histogram is the frequency distribution of the gray levels with the number of
 * pure black values displayed on the left and number of pure white values on the right.
 * Note that this sketch will behave differently on Android, since most images will
 * no longer be full 24-bit color.
 */

let img;
let hist = [];

function preload() {
  // Load an image from the data directory
  // Load a different image by modifying the comments
  // img = loadImage('assets/frontier.jpg');
  img = loadImage('../../../../p5js-website-legacy-examples/assets/frontier.jpg');
}

function setup() {
  // createCanvas(640, 360);
  createCanvas(windowWidth, windowHeight);
  image(img, 0, 0);

  // Initialize the histogram
  for (let i = 0; i < 100; i++) {
    hist.push(0);
  }

  // Calculate the histogram
  for (let i = 0; i < img.width; i++) {
    for (let j = 0; j < img.height; j++) {
      let bright = int(brightness(img.get(i, j)));
      hist[bright]++;
    }
  }
}

function draw(){
  // Find the largest value in the histogram
  let histMax = max(hist);
  stroke(255);
  // Draw half of the histogram (skip every second value)
  for (let i = 0; i < img.width; i += 2) {
    // Map i (from 0..img.width) to a location in the histogram (0..100)
    let which = int(map(i, 0, img.width, 0, 100));
    // Convert the histogram value to a location between
    // the bottom and the top of the picture
    let y = int(map(hist[which], 0, histMax, img.height, 0));
    line(i, img.height, i, y);
  }
}