dount_example.js

(function() {
var _onload = function() {
  var pretag = document.getElementById('d');
  var canvastag = document.getElementById('canvasdonut');

  var tmr1 = undefined, tmr2 = undefined;
  var A=1, B=1;

  // This is copied, pasted, reformatted, and ported directly from my original
  // donut.c code
  var asciiframe=function() {
    var b=[];
    var z=[];
    A += 0.07;
    B += 0.03;
    var cA=Math.cos(A), sA=Math.sin(A),
        cB=Math.cos(B), sB=Math.sin(B);
    for(var k=0;k<1760;k++) {
      b[k]=k%80 == 79 ? "\n" : " ";
      z[k]=0;
    }
    for(var j=0;j<6.28;j+=0.07) { // j <=> theta
      var ct=Math.cos(j),st=Math.sin(j);
      for(i=0;i<6.28;i+=0.02) {   // i <=> phi
        var sp=Math.sin(i),cp=Math.cos(i),
            h=ct+2, // R1 + R2*cos(theta)
            D=1/(sp*h*sA+st*cA+5), // this is 1/z
            t=sp*h*cA-st*sA; // this is a clever factoring of some of the terms in x' and y'

        var x=0|(40+30*D*(cp*h*cB-t*sB)),
            y=0|(12+15*D*(cp*h*sB+t*cB)),
            o=x+80*y,
            N=0|(8*((st*sA-sp*ct*cA)*cB-sp*ct*sA-st*cA-cp*ct*sB));
        if(y<22 && y>=0 && x>=0 && x<79 && D>z[o])
        {
          z[o]=D;
          b[o]=".,-~:;=!*#$@"[N>0?N:0];
        }
      }
    }
    pretag.innerHTML = b.join("");
  };

  window.anim1 = function() {
    if(tmr1 === undefined) {
      tmr1 = setInterval(asciiframe, 50);
    } else {
      clearInterval(tmr1);
      tmr1 = undefined;
    }
  };

  // This is a reimplementation according to my math derivation on the page
  var R1 = 1;
  var R2 = 2;
  var K1 = 150;
  var K2 = 5;
  var canvasframe=function() {
    var ctx = canvastag.getContext('2d');
    ctx.fillStyle='#000';
    ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);

    if(tmr1 === undefined) { // only update A and B if the first animation isn't doing it already
      A += 0.07;
      B += 0.03;
    }
    // precompute cosines and sines of A, B, theta, phi, same as before
    var cA=Math.cos(A), sA=Math.sin(A),
        cB=Math.cos(B), sB=Math.sin(B);
    for(var j=0;j<6.28;j+=0.3) { // j <=> theta
      var ct=Math.cos(j),st=Math.sin(j); // cosine theta, sine theta
      for(i=0;i<6.28;i+=0.1) {   // i <=> phi
        var sp=Math.sin(i),cp=Math.cos(i); // cosine phi, sine phi
        var ox = R2 + R1*ct, // object x, y = (R2,0,0) + (R1 cos theta, R1 sin theta, 0)
            oy = R1*st;

        var x = ox*(cB*cp + sA*sB*sp) - oy*cA*sB; // final 3D x coordinate
        var y = ox*(sB*cp - sA*cB*sp) + oy*cA*cB; // final 3D y
        var ooz = 1/(K2 + cA*ox*sp + sA*oy); // one over z
        var xp=(150+K1*ooz*x); // x' = screen space coordinate, translated and scaled to fit our 320x240 canvas element
        var yp=(120-K1*ooz*y); // y' (it's negative here because in our output, positive y goes down but in our 3D space, positive y goes up)
        // luminance, scaled back to 0 to 1
        var L=0.7*(cp*ct*sB - cA*ct*sp - sA*st + cB*(cA*st - ct*sA*sp));
        if(L > 0) {
          ctx.fillStyle = 'rgba(255,255,255,'+L+')';
          ctx.fillRect(xp, yp, 1.5, 1.5);
        }
      }
    }
  }


  window.anim2 = function() {
    if(tmr2 === undefined) {
      tmr2 = setInterval(canvasframe, 50);
    } else {
      clearInterval(tmr2);
      tmr2 = undefined;
    }
  };

  asciiframe();
  canvasframe();
}

if(document.all)
  window.attachEvent('onload',_onload);
else
  window.addEventListener("load",_onload,false);
})();