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run = function() {
var
canvas = document.body.children[0],
ctx = canvas.getContext('2d'),
floor = Math.floor,
W = innerWidth, // canvas width
H = canvas.height = innerHeight-12, // canvas height
CW = 800,
SW = W / CW, // scale for virtual canvas width. canvas is scaled so that pixel width = W / 800
CH = H / SW, // transformed height
U = 40, // width of world blocks
sprites = ['A5.1VEg254m6','A5..UoS201XU','41UfpSMDAg2+','MC05WlC45WM2'],// anim frames (second last frame is jump up, last frame is jump down)
K = 1, // level selection
rand1 = 65537, // part of Park-Miller random number generator
jump;  // boolean, are we jumping?

// Scale canvas
//ctx.scale(W / CW, W / CW);

function G() {
  K = parseInt(prompt('Lvl', K));
  jump = 0;
   var
  N = n = 75, // iteration variable - no of generatings
  L = K, // level
  terrain = [], // terrain heightmap
  xCamera = 0, // camera x position in world coords
  lastXCamera = 0,
  vxCamera = 4, // camera x velocity
  xPlayer = 50, // player x position
  vyPlayer = 0, // player vertical velocity
  s = 0, // sprite animation index
  I = i = 0, // I = number of blocks, i = temp iteration variable
  yPlayer, // player y position
  d,e, // Time at last frame & temp variable
  sprite, // animation frame
  temp1,temp2; // temp vars
  function R() {
    return (L = L * N % rand1) / rand1;
  };
  function fillRect(x,y,w,h) {
    ctx.fillRect(x*SW, y*SW, w*SW, h*SW);
  };
  function l() {
    e = new Date().getTime();
    canvas.width = W;
    
    // d = milliseconds in last frame
    d = d ? (e - d) / 10 : 0;
    vxCamera += .004 * d;
    lastXCamera = xCamera;
    xCamera += vxCamera * d;
    
    // physics
    // move player forward
    xPlayer += vxCamera * d;
    // temp1 = terrain position at player x position
    temp2 = temp1;
    temp1 = terrain[floor(xPlayer / U)];
    
    // oh no we're underground, undo our move player Forward
    if (yPlayer < temp1) {
      xPlayer -= vxCamera * d;
      temp1 = temp2;
    }
    
    vyPlayer = 
      jump ?
        yPlayer == temp1 ? 
          // on ground, start jump
          2
        : 
          // decelerate fall
          vyPlayer -.015 * d
      :
        vyPlayer > 0 ?
          // start fall
          0
        :
          // decelerate fall
          vyPlayer - .05 * d;
    
    yPlayer >= temp1 && yPlayer + vyPlayer * d < temp1 ? (
      // hit ground
      yPlayer = temp1,
      vyPlayer = 0,
      
      // player on ground, accelerate
      xPlayer += .05 * d * d,
      
      // increase anim frame
      s += .07 * d,
      s = s % 2
    ) : (
      yPlayer += vyPlayer * d,
      
      // anim
      s = vyPlayer > 0 ? 2.8 : 3.8 // +.8 so run will start again as soon as we land
    );
    
    i = I;
    while (i--) {
      fillRect(i * U - xCamera, CH, U, -terrain[i]);
    }
    // draw only relevant rects
    //i = floor(lastXCamera / U);
    //while (i < floor((xCamera + W) / U) + 2 && i < I) {
    //  // draw whole quad:
    //  fillRect(i * U - xCamera, CH, U, -terrain[i]);
    //  ++i;
    //}
    
    // draw dude
    sprite = sprites[floor(s)], // animation frame
    i = 72;
    while (i) {
      if (i-- % 6 === 0) {
        // temp1 = base64 code for current sprite char
        temp1 = sprite.charCodeAt(i/6);
        // temp2 = unencoded base64 value
        temp2 = temp1 < 44 ? 0 : temp1 < 47 ? 1 : temp1 < 58 ? temp1 - 46 : temp1 < 91 ? temp1 - 53 : temp1 - 59;
      }
      if (temp2 % 2) {
        fillRect(xPlayer - xCamera - 7 + (i % 7),
          CH - yPlayer - 10 + floor(i / 7), 1, 1);
      }
      temp2 >>>= 1;
    }
    
    // draw progress meter
    fillRect(5, 5, xCamera * CW / I / U, 5);
    
    // death
    xPlayer > I*U+U ? (
      ++K,
      G()
    ) : xPlayer < xCamera ? (
      G()
    ) : (
      setTimeout(l, 15 - d * 10),
      d = e
    );
  };
  while (n) {
    // temp1  = width var when generating
    temp1 = n-- == N ? 30 : floor(R() * (n % 2 ? 4 : 9)) + (n % 2 ? 2 : 5);
    // temp2 = height var when generating
    temp2 = n % 2 ? 0 : 9 + R() * 80 + K; // every second block is small
    //temp2 = 2;
    I += temp1;
    while (temp1--) {
      terrain[i + temp1] = floor(temp2);
    }
    i = I;
  }
  yPlayer = terrain[0];
  
  d = 0;
  l();
}
onkeydown = onkeyup = function(e) {
  // Thanks @marijnjh
  jump = e.type[5];
};
setTimeout(G, 1);
}();