Fire JS Bin - Burn-Canvas - 2

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// Copyright by Krzysztof Pasek (www.guciek.net)
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, version 2 or 3.

function mouse() {
  var ob = {
    x: -1,
    y: -1,
    pressed: false
  };

function onmove(e) {
    ob.x = e.clientX;
    ob.y = e.clientY;
  }

function ondown() {
    ob.pressed = true;
  }

function onup() {
    ob.pressed = false;
  }
  document.addEventListener('mousemove', onmove, false);
  document.addEventListener('mousedown', ondown, false);
  document.addEventListener('mouseup', onup, false);
  return ob;
}

function draw() {
  var w, h, c;
  var reach = 50;
  var m = mouse();
  var lastmx = 0,
      lastmy = 0;

function init() {
    w = window.innerWidth;
    h = window.innerHeight;
    var elem = document.getElementById("view");
    elem.width = w;
    elem.height = h;
    c = elem.getContext("2d");
    c.lineCap = "round";
    c.strokeStyle = "rgb(255,255,255)";
    c.fillStyle = "rgb(255,255,255)";
    c.fillRect(0, 0, w, h);
  }

function modify_region(i, centerx, centery) {
    if (m.pressed) {
      for (var y = i.height - 1; y >= 0; y--) {
        for (var x = 0; x < i.width; x++) {
          var pos = 4 * (i.width * y + x);
          var a = x - centerx;
          var b = y - centery;
          var v = 1 - (a * a + b * b) / (reach * reach);
          if (v < 0) {
            v = 0;
          }
          v = v * v;
          if (y >= 1) {
            i.data[pos + 0] += v * (i.data[pos + 0 - i.width * 4] - i.data[pos + 0]);
            i.data[pos + 1] += v * (i.data[pos + 1 - i.width * 4] - i.data[pos + 1]);
            i.data[pos + 2] += v * (i.data[pos + 2 - i.width * 4] - i.data[pos + 2]);
          }
        }
      }
    } else {
      // This part is more optimized for fast execution.
      var rr = 1 / (reach * reach);
      var pos = 0;
      var w = i.width;
      var t = 0;
      var v = 0;
      var a = 0;
      var vv = 0;
      var idata = i.data;
      for (var y = 0; y < i.height; y++) {
        var b = y - centery;
        var bb = b * b;
        for (var x = 0; x < w; x++) {
          a = x - centerx;
          v = 1 - (a * a + bb) * rr;
          if (v <= 0) {
            pos += 4;
            continue;
          }
          vv = v * v;
          v = 6 * (vv - vv * v);
          t = idata[pos];
          t -= v * 10;
          if (t < 0) t += 256;
          idata[pos] = t;
          pos++;
          t = idata[pos];
          t -= v * 21.23553;
          if (t < 0) t += 256;
          idata[pos] = t;
          pos++;
          t = idata[pos];
          t -= v * 46.72232;
          if (t < 0) t += 256;
          idata[pos] = t;
          pos += 2;
        }
      }
    }
  }

function do_draw() {
    if (m.x < 0) {
      return;
    }
    if ((lastmx == m.x) && (lastmy == m.y)) {
      if (reach < 100) {
        reach++;
      }
    } else {
      lastmx = m.x;
      lastmy = m.y;
      reach = 50;
    }
    var x1 = m.x - reach;
    var x2 = m.x + reach;
    var y1 = m.y - reach;
    var y2 = m.y + reach;
    if (x1 < 0) {
      x1 = 0;
    }
    if (y1 < 0) {
      y1 = 0;
    }
    if (x1 > w - 1) {
      x1 = w - 1;
    }
    if (y1 > h - 1) {
      y1 = h - 1;
    }
    if (x2 > w) {
      x2 = w;
    }
    if (y2 > h) {
      y2 = h;
    }
    if (x2 < x1 + 1) {
      x2 = x1 + 1;
    }
    if (y2 < y1 + 1) {
      y2 = y1 + 1;
    }
    var i = c.getImageData(x1, y1, x2 - x1, y2 - y1);
    modify_region(i, m.x - x1, m.y - y1);
    c.putImageData(i, x1, y1);
  }
  return {
    draw: do_draw,
    init: init
  };
}

function timer() {
  var d = draw();

function step() {
    try {
      d.draw();
      setTimeout(step, 8);
    } catch (err) {
      alert("Error: " + err);
      throw err;
    }
  }

function start() {
    try {
      d.init();
      setTimeout(step, 1);
    } catch (err) {
      alert("Error: " + err);
      throw err;
    }
  }
  return {
    start: start
  };
}
setTimeout(timer().start, 100);