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// Contains code from http: //learningwebgl.com/blog/ ? p=28#triangle-vertex-positions 
// modified to produce a subdivision algorithm for rendering Bezier
// patches with WebGL

var gl;

class Material {
    constructor(baseColor, emissive, specular, roughness, metallic, f0) {
        this.baseColor = baseColor;
        this.emissive = emissive;
        this.specular = specular;
        this.roughness = roughness;
        this.metallic = metallic;
        this.f0 = f0;
    }

    setUniform(program, stringLoc, index=null) {
        var getLoc;
        if (index===null) {
            getLoc =
            param => gl.getUniformLocation(program, stringLoc + "." + param);
        } else {
            getLoc =
            param => gl.getUniformLocation(program, stringLoc + "[" + index + "]." + param);
        }

        gl.uniform4fv(getLoc("baseColor"), new Float32Array(this.baseColor));
        gl.uniform4fv(getLoc("emissive"), new Float32Array(this.emissive));
        gl.uniform4fv(getLoc("specular"), new Float32Array(this.specular));

        gl.uniform1f(getLoc("roughness"), this.roughness);
        gl.uniform1f(getLoc("metallic"), this.metallic);
        gl.uniform1f(getLoc("f0"), this.f0);
    }
}

var enumPointLight = 1;
var enumDirectionalLight = 2;

class Light {
    constructor(type, lightColor, brightness, customParam) {
        this.type = type;
        this.lightColor = lightColor;
        this.brightness = brightness;
        this.customParam = customParam;
    }

    setUniform(program, stringLoc, index) {
        var getLoc =
            param => gl.getUniformLocation(program, stringLoc + "[" + index + "]." + param);

        gl.uniform1i(getLoc("type"), this.type);
        gl.uniform3fv(getLoc("color"), new Float32Array(this.lightColor));
        gl.uniform1f(getLoc("brightness"), this.brightness);
        gl.uniform4fv(getLoc("parameter"), new Float32Array(this.customParam));
    }
}

function initGL(canvas) {
    try {
        gl = canvas.getContext("webgl2");
        gl.viewportWidth = canvas.width;
        gl.viewportHeight = canvas.height;
    } catch (e) {}
    if (!gl) {
        alert("Could not initialize WebGL");
    }
}

function getShader(gl, id) {
    var shaderScript = document.getElementById(id);
    if (!shaderScript) {
        return null;
    }
    var str = "";
    var k = shaderScript.firstChild;
    while (k) {
        if (k.nodeType == 3) {
            str += k.textContent;
        }
        k = k.nextSibling;
    }
    var shader;
    if (shaderScript.type == "x-shader/x-fragment") {
        shader = gl.createShader(gl.FRAGMENT_SHADER);
    } else if (shaderScript.type == "x-shader/x-vertex") {
        shader = gl.createShader(gl.VERTEX_SHADER);
    } else {
        return null;
    }
    gl.shaderSource(shader, str);
    gl.compileShader(shader);
    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
        alert(gl.getShaderInfoLog(shader));
        return null;
    }
    return shader;
}

function resetCamera() {
    cameraPos = vec3.fromValues(0, 0, 2);
    cameraLookAt = vec3.fromValues(0, 0, 0);
    cameraUp = vec3.fromValues(1, 0, 0);
    sceneSetup();
    redraw=true;
}

var shaderProgram;

function initShaders() {
    var fragmentShader = getShader(gl, "shader-fs");
    var vertexShader = getShader(gl, "shader-vs");
    shaderProgram = gl.createProgram();
    gl.attachShader(shaderProgram, vertexShader);
    gl.attachShader(shaderProgram, fragmentShader);
    gl.linkProgram(shaderProgram);
    if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
        alert("Could not initialize shaders");
    }
    gl.useProgram(shaderProgram);

    shaderProgram.vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
    gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);
    shaderProgram.vertexColorAttribute = gl.getAttribLocation(shaderProgram, "aVertexColor");
    gl.enableVertexAttribArray(shaderProgram.vertexColorAttribute);
    shaderProgram.vertexNormalAttribute = gl.getAttribLocation(shaderProgram, "aVertexNormal");
    gl.enableVertexAttribArray(shaderProgram.vertexNormalAttribute);

    shaderProgram.vertexMaterialIndexAttribute = gl.getAttribLocation(shaderProgram, "aVertexMaterialIndex");
    gl.enableVertexAttribArray(shaderProgram.vertexMaterialIndexAttribute);
    

    shaderProgram.pMatrixUniform = gl.getUniformLocation(shaderProgram, "uPMatrix");
    shaderProgram.mMatrixUniform = gl.getUniformLocation(shaderProgram, "uMMatrix");
    shaderProgram.vMatrixUniform = gl.getUniformLocation(shaderProgram, "uVMatrix");
    shaderProgram.nlightsUniform = gl.getUniformLocation(shaderProgram, "unLights");
    shaderProgram.useColorUniform = gl.getUniformLocation(shaderProgram, "useColor");
    
}


// math aux functions 
function degToRad(degrees) {
    return degrees * Math.PI / 180;
}
function unit(v) {
    var norm = Math.sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]);
    norm = (norm != 0) ? 1 / norm : 1;
    return [v[0] * norm, v[1] * norm, v[2] * norm];
}

function abs2(v) {
return v[0] * v[0] + v[1] * v[1] + v[2] * v[2];
}

function dot(u, v) {
return u[0] * v[0] + u[1] * v[1] + u[2] * v[2];
}

function cross(u, v) {
return [u[1] * v[2] - u[2] * v[1],
    u[2] * v[0] - u[0] * v[2],
    u[0] * v[1] - u[1] * v[0]
];
}
// return the perpendicular distance squared of a point z from the plane
// through u with unit normal n.
function Distance2(z, u, n) {
    var d = dot([z[0] - u[0], z[1] - u[1], z[2] - u[2]], n);
    return d * d;
}

var vMatrix = mat4.create();
var mMatrix = mat4.create();
var pMatrix = mat4.create();

var headlamp = new Light(
  type = enumDirectionalLight,
  lightColor = [1, 0.87, 0.745],
  brightness = 1,
  customParam = [0, 0, 1, 0]
);

function setUniforms() {
  gl.uniformMatrix4fv(shaderProgram.vMatrixUniform, false, vMatrix);
  gl.uniformMatrix4fv(shaderProgram.pMatrixUniform, false, pMatrix);
  gl.uniformMatrix4fv(shaderProgram.mMatrixUniform, false, mMatrix);

  objMaterial.setUniform(shaderProgram, "objMaterial", 0);

  // for now, if we simulate headlamp. Can also specify custom lights later on...
  headlamp.setUniform(shaderProgram, "objLights", 0);
  gl.uniform1i(shaderProgram.nlightsUniform, 1);
  gl.uniform1i(shaderProgram.useColorUniform, 0);

}

var VertexBuffer;
var ColorBuffer;
var NormalBuffer;

// base buffer arrays
var vertices = new Array();
var colors = new Array();
var normals = new Array();
var indices = new Array();
var materials = new Array();

// no. of verts.
var nvertices = 0;

var mMatrixStack = [];
var pMatrix = mat4.create();
var viewMatrix = mat4.create();
var localRotation = mat4.create();

function mvPushMatrix() {
  var copy = mat4.create();
  mat4.set(mMatrix, copy);
  mMatrixStack.push(copy);
}

function mvPopMatrix() {
  if (mMatrixStack.length == 0) {
    throw "Invalid popMatrix!";
  }
  mMatrix = mMatrixStack.pop();
}

var redraw = true;
var mouseDownOrTouchActive = false;
var lastMouseX = null;
var lastMouseY = null;
var touchID = null;


var center = [0, 0, 1];
var centerInv = [0, 0, -1];

var rotationMatLocal = mat4.create();
var rotationMatrix = mat4.create();
mat4.identity(rotationMatrix);

function handleMouseDown(event) {
  mouseDownOrTouchActive = true;
  lastMouseX = event.clientX;
  lastMouseY = event.clientY;
}

function handleTouchStart(evt) {
  evt.preventDefault();
  var touches = evt.targetTouches;

  if (touches.length == 1 && !mouseDownOrTouchActive) {
    touchId = touches[0].identifier;
    lastMouseX = touches[0].pageX,
      lastMouseY = touches[0].pageY;
  }
}

function handleMouseUpOrTouchEnd(event) {
  mouseDownOrTouchActive = false;
}

function processDrag(newX, newY, pan = false) {
  let lastX = (lastMouseX - 400) / 400;
  let lastY = (lastMouseY - 400) / 400;

  let rawX = (newX - 400) / 400;
  let rawY = (newY - 400) / 400;

  let viewmatInv = mat4.create();
  mat4.invert(viewmatInv, vMatrix);

  let tmpCameraOffset = vec3.create();
  vec3.subtract(tmpCameraOffset, cameraPos, cameraLookAt);

  if (!pan) {
    let [angle, axis] = arcballLib.arcball([lastX, -lastY], [rawX, -rawY]);

    if (angle == NaN || axis == NaN) {
      console.error("Angle or axis NaN!");
      return;
    }

    let depthVec = vec3.clone(cameraLookAt);
    vec3.transformMat4(depthVec, depthVec, vMatrix);
    //vec3.transformMat4(depthVec, depthVec, pMatrix);
    vec3.add(axis, axis, depthVec);

    // let projMatInv=mat4.create();
    // mat4.invert(projMatInv, pMatrix);

    //vec3.transformMat4(axis,axis,projMatInv);
    vec3.transformMat4(axis, axis, viewmatInv);

    let tmpRotMat = mat4.create();

    mat4.fromRotation(tmpRotMat, -angle, axis);

    vec3.transformMat4(tmpCameraOffset, tmpCameraOffset, tmpRotMat);
    vec3.transformMat4(cameraUp, cameraUp, tmpRotMat);

    vec3.add(cameraPos, tmpCameraOffset, cameraLookAt);


  } else {
    let xTransl = (rawX - lastX);
    let yTransl = (rawY - lastY);
    let normCameraUp = vec3.create();
    vec3.normalize(normCameraUp, cameraUp);
    vec3.scale(normCameraUp, normCameraUp, yTransl);

    let normCameraLeft = vec3.create();
    vec3.cross(normCameraLeft, tmpCameraOffset, cameraUp);
    vec3.normalize(normCameraLeft, normCameraLeft);
    vec3.scale(normCameraLeft, normCameraLeft, xTransl);

    let cameraShift = vec3.create();
    vec3.add(cameraShift, normCameraUp, normCameraLeft);

    vec3.add(cameraLookAt, cameraLookAt, cameraShift);
    vec3.add(cameraPos, cameraPos, cameraShift);
  }

  lastMouseX = newX;
  lastMouseY = newY;
  redraw = true;
}

function handleKey(key) {
  var keycode = key.key;
  var rotate = true;
  var axis = [0, 0, 1];
  switch (keycode) {
    case "w":
      axis = [-1, 0, 0];
      break;
    case "d":
      axis = [0, 1, 0];
      break;
    case "a":
      axis = [0, -1, 0];
      break;
    case "s":
      axis = [1, 0, 0];
      break;
    case "h":
      resetCamera();
      break;
    default:
      rotate = false;
      break;
  }

  if (rotate) {
    mat4.rotate(rotationMatrix, rotationMatrix, 0.1, axis);
    redraw = true;
  }

}

function handleMouseWheel(event) {
  let zoomFactor = event.deltaY / 50;

  // console.log(zoomFactor);

  let cameraShift = vec3.create();
  vec3.subtract(cameraShift, cameraPos, cameraLookAt);

  let cameraDir = vec3.create();
  vec3.normalize(cameraDir, cameraShift);
  vec3.scale(cameraDir, cameraDir, zoomFactor);

  let newCameraShift = vec3.create();
  vec3.add(newCameraShift, cameraShift, cameraDir);

  // not go beyond the bounds 
  if (vec3.length(newCameraShift) < 0.01 && zoomFactor < 0) {

  } else if (vec3.length(newCameraShift) > 100 && zoomFactor > 0) {

  } else if (vec3.dot(newCameraShift, cameraShift) >= 0) {
    cameraShift = vec3.clone(newCameraShift);
  }

  vec3.add(cameraPos, cameraShift, cameraLookAt);

  res = 1 / (vec3.length(cameraShift) + 0.001) * 0.001;
  redraw = true;
}

function handleMouseMove(event) {
  if (!mouseDownOrTouchActive) {
    return;
  }

  var newX = event.clientX;
  var newY = event.clientY;

  processDrag(newX, newY, event.getModifierState("Alt"));
}

function handleTouchMove(evt) {
  evt.preventDefault();
  var touches = evt.targetTouches;

  if (touches.length == 1 && touchId == touches[0].identifier) {
    var newX = touches[0].pageX;
    var newY = touches[0].pageY;
    processDrag(newX, newY);
  }
}

// Prepare canvas for drawing
function sceneSetup() {
  gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
  gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
  mat4.perspective(pMatrix, 45, gl.viewportWidth / gl.viewportHeight, 0.1, 100.0);

  mat4.lookAt(vMatrix, cameraPos, cameraLookAt, cameraUp);
  mat4.identity(mMatrix);
}

var indexExt;

// Create buffer data for the patch and its subdivisions to be pushed to the graphics card
//Takes as an argument the array of vertices that define the patch to be drawn 
// Using the vertex position buffer of the above function,draw patch.
function setBuffer() {
  VertexBuffer = gl.createBuffer();
  VertexBuffer.itemSize = 3;

  ColorBuffer = gl.createBuffer();
  ColorBuffer.itemSize = 4;

  NormalBuffer = gl.createBuffer();
  NormalBuffer.itemSize = 3;

  MaterialIndexBuffer = gl.createBuffer();
  MaterialIndexBuffer.itemSize = 1;

  indexBuffer = gl.createBuffer();
  indexBuffer.itemSize = 1;

  setUniforms();
  indexExt = gl.getExtension("OES_element_index_uint");
}

function drawBuffer() {
  gl.bindBuffer(gl.ARRAY_BUFFER, VertexBuffer);
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
  gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute,
    VertexBuffer.itemSize, gl.FLOAT, false, 0, 0);
  VertexBuffer.numItems = nvertices;

  // FIXME: Some kind of a conditional here for colors??? 
  // along a flag of "useColors or something??? "
  gl.bindBuffer(gl.ARRAY_BUFFER, ColorBuffer);
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(colors), gl.STATIC_DRAW);
  gl.vertexAttribPointer(shaderProgram.vertexColorAttribute,
    ColorBuffer.itemSize, gl.FLOAT, false, 0, 0);
  ColorBuffer.numItems = nvertices;

  gl.bindBuffer(gl.ARRAY_BUFFER, NormalBuffer);
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(normals), gl.STATIC_DRAW);
  gl.vertexAttribPointer(shaderProgram.vertexNormalAttribute,
    NormalBuffer.itemSize, gl.FLOAT, false, 0, 0);
  NormalBuffer.numItems = nvertices;

  gl.bindBuffer(gl.ARRAY_BUFFER, MaterialIndexBuffer);
  gl.bufferData(gl.ARRAY_BUFFER, new Int32Array(materials), gl.STATIC_DRAW);
  gl.vertexAttribIPointer(shaderProgram.vertexMaterialIndexAttribute,
    MaterialIndexBuffer.itemSize, gl.INT,false,0,0);
  MaterialIndexBuffer.numItems = nvertices;

  gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer);
  gl.bufferData(gl.ELEMENT_ARRAY_BUFFER,
    indexExt ? new Uint32Array(indices) : new Uint16Array(indices),
    gl.STATIC_DRAW);
  indexBuffer.numItems = indices.length;

  gl.drawElements(gl.TRIANGLES, indexBuffer.numItems,
    indexExt ? gl.UNSIGNED_INT : gl.UNSIGNED_SHORT, 0);
  vertices = [];
  colors = [];
  normals = [];
  indices = [];
  materials = [];
  nvertices = 0;
}

var pixel = 1.0; // Adaptive rendering constant.
var FillFactor = 0.1;
var BezierFactor = 0.4;
//var res=0.0005; // Temporary
var res = 0.001; // Temporary
var res2 = res * res;
var Epsilon = 0.1 * res;
var epsilon = 0;
var Fuzz = 1000 * Number.EPSILON;
var Fuzz2 = Fuzz * Fuzz;

function Split3(z0, c0, c1, z1) {
  this.m0 = new Array(3);
  this.m2 = new Array(3);
  this.m3 = new Array(3);
  this.m4 = new Array(3);
  this.m5 = new Array(3);
  for (var i = 0; i < 3; ++i) {
    this.m0[i] = 0.5 * (z0[i] + c0[i]);
    var m1 = 0.5 * (c0[i] + c1[i]);
    this.m2[i] = 0.5 * (c1[i] + z1[i]);
    this.m3[i] = 0.5 * (this.m0[i] + m1);
    this.m4[i] = 0.5 * (m1 + this.m2[i]);
    this.m5[i] = 0.5 * (this.m3[i] + this.m4[i]);
  }
}


// Store the vertex v and its color vector c in the buffer.
function vertex(v, c, n) {
  vertices.push(v[0]);
  vertices.push(v[1]);
  vertices.push(v[2]);

  colors.push(c[0]);
  colors.push(c[1]);
  colors.push(c[2]);
  colors.push(c[3]);

  normals.push(n[0]);
  normals.push(n[1]);
  normals.push(n[2]);

  // FIXME: Enable arbitrary materials? 
  materials.push(materialIndex);

  return nvertices++;
}

function normal(left3, left2, left1, middle, right1, right2, right3) {
  var u0 = right1[0] - middle[0];
  var v0 = left1[0] - middle[0];
  var u1 = right1[1] - middle[1];
  var v1 = left1[1] - middle[1];
  var u2 = right1[2] - middle[2];
  var v2 = left1[2] - middle[2];
  var n = [
    u1 * v2 - u2 * v1,
    u2 * v0 - u0 * v2,
    u0 * v1 - u1 * v0
  ];
  if (abs2(n) > epsilon)
    return unit(n);

  var lp = [v0, v1, v2];
  var rp = [u0, u1, u2];
  var lpp = [middle[0] + left2[0] - 2 * left1[0],
    middle[1] + left2[1] - 2 * left1[1],
    middle[2] + left2[2] - 2 * left1[2]
  ];
  var rpp = [middle[0] + right2[0] - 2 * right1[0],
    middle[1] + right2[1] - 2 * right1[1],
    middle[2] + right2[2] - 2 * right1[2]
  ];
  var a = cross(rpp, lp);
  var b = cross(rp, lpp);
  n = [a[0] + b[0],
    a[1] + b[1],
    a[2] + b[2]
  ];
  if (abs2(n) > epsilon)
    return unit(n);

  var lppp = [left3[0] - middle[0] + 3 * (left1[0] - left2[0]),
    left3[1] - middle[1] + 3 * (left1[1] - left2[1]),
    left3[2] - middle[2] + 3 * (left1[2] - left2[2])
  ];
  var rppp = [right3[0] - middle[0] + 3 * (right1[0] - right2[0]),
    right3[1] - middle[1] + 3 * (right1[1] - right2[1]),
    right3[2] - middle[2] + 3 * (right1[2] - right2[2])
  ];
  a = cross(rpp, lpp);
  b = cross(rp, lppp);
  var c = cross(rppp, lp);
  var d = cross(rppp, lpp);
  var e = cross(rpp, lppp);
  var f = cross(rppp, lppp);
  return unit([9 * a[0] + 3 * (b[0] + c[0] + d[0] + e[0]) + f[0],
    9 * a[1] + 3 * (b[1] + c[1] + d[1] + e[1]) + f[1],
    9 * a[2] + 3 * (b[2] + c[2] + d[2] + e[2]) + f[2]
  ]);
}

// return the maximum distance squared of points c0 and c1 from 
// the respective internal control points of z0--z1.
function Straightness(z0, c0, c1, z1) {
  var third = 1.0 / 3.0;
  var v = [third * (z1[0] - z0[0]), third * (z1[1] - z0[1]), third * (z1[2] - z0[2])];
  return Math.max(abs2([c0[0] - v[0] - z0[0], c0[1] - v[1] - z0[1], c0[2] - v[2] - z0[2]]),
    abs2([z1[0] - v[0] - c1[0], z1[1] - v[1] - c1[1], z1[2] - v[2] - c1[2]]));
}

// return the maximum perpendicular distance squared of points c0 and c1
// from z0--z1.
function Distance1(z0, c0, c1, z1) {
  var Z0 = [c0[0] - z0[0], c0[1] - z0[1], c0[2] - z0[2]];
  var Q = unit([z1[0] - z0[0], z1[1] - z0[1], z1[2] - z0[2]]);
  var Z1 = [c1[0] - z0[0], c1[1] - z0[1], c1[2] - z0[2]];
  var p0 = dot(Z0, Q);
  var p1 = dot(Z1, Q);
  return Math.max(abs2([Z0[0] - p0 * Q[0], Z0[1] - p0 * Q[1], Z0[2] - p0 * Q[2]]),
    abs2([Z1[0] - p1 * Q[0], Z1[1] - p1 * Q[1], Z1[2] - p1 * Q[2]]));
}


function Distance(p) {
  var p0 = p[0];
  var p3 = p[3];
  var p12 = p[12];
  var p15 = p[15];

  // Check the flatness of the quad.
  var d = Distance2(p15, p0, normal(p3, p[2], p[1], p0, p[4], p[8], p12));

  // Determine how straight the edges are.
  d = Math.max(d, Straightness(p0, p[1], p[2], p3));
  d = Math.max(d, Straightness(p0, p[4], p[8], p12));
  d = Math.max(d, Straightness(p3, p[7], p[11], p15));
  d = Math.max(d, Straightness(p12, p[13], p[14], p15));

  // Determine how straight the interior control curves are.
  d = Math.max(d, Straightness(p[4], p[5], p[6], p[7]));
  d = Math.max(d, Straightness(p[8], p[9], p[10], p[11]));
  d = Math.max(d, Straightness(p[1], p[5], p[9], p[13]));
  return Math.max(d, Straightness(p[2], p[6], p[10], p[14]));
}

var k = 1;
// Return color associated with unit normal vector n.
function color(n) {
  var Ldotn = Math.abs(L[0] * n[0] + L[1] * n[1] + L[2] * n[2]);
  var p = [emissive[0] + ambient[0] * Ambient[0] + Ldotn * diffuse[0] * Diffuse[0],
    emissive[1] + ambient[1] * Ambient[1] + Ldotn * diffuse[1] * Diffuse[1],
    emissive[2] + ambient[2] * Ambient[2] + Ldotn * diffuse[2] * Diffuse[2]
  ];
  var s = shininess * 128;
  var H = unit([L[0], L[1], L[2] + 1]);
  var f = Math.pow(H[0] * n[0] + H[1] * n[1] + H[2] * n[2], s);

  // Phong-Blinn model of specular reflection
  p = [p[0] + f * specular[0] * Specular[0], p[1] + f * specular[1] * Specular[1],
    p[2] + f * specular[2] * Specular[2]
  ];

  return [p[0], p[1], p[2], 1];
}

function render(p, I0, I1, I2, I3, P0, P1, P2, P3, flat0, flat1, flat2, flat3,
  C0, C1, C2, C3) {
  if (Distance(p) < res2) { // Patch is flat
    indices.push(I0);
    indices.push(I1);
    indices.push(I2);

    indices.push(I0);
    indices.push(I2);
    indices.push(I3);
    return;
  }

  var p0 = p[0];
  var p3 = p[3];
  var p12 = p[12];
  var p15 = p[15];

  var c0 = new Split3(p0, p[1], p[2], p3);
  var c1 = new Split3(p[4], p[5], p[6], p[7]);
  var c2 = new Split3(p[8], p[9], p[10], p[11]);
  var c3 = new Split3(p12, p[13], p[14], p15);
  var c4 = new Split3(p0, p[4], p[8], p12);
  var c5 = new Split3(c0.m0, c1.m0, c2.m0, c3.m0);
  var c6 = new Split3(c0.m3, c1.m3, c2.m3, c3.m3);
  var c7 = new Split3(c0.m5, c1.m5, c2.m5, c3.m5);
  var c8 = new Split3(c0.m4, c1.m4, c2.m4, c3.m4);
  var c9 = new Split3(c0.m2, c1.m2, c2.m2, c3.m2);
  var c10 = new Split3(p3, p[7], p[11], p15);

  var s0 = [p0, c0.m0, c0.m3, c0.m5, c4.m0, c5.m0, c6.m0, c7.m0,
    c4.m3, c5.m3, c6.m3, c7.m3, c4.m5, c5.m5, c6.m5, c7.m5
  ];
  var s1 = [c4.m5, c5.m5, c6.m5, c7.m5, c4.m4, c5.m4, c6.m4, c7.m4,
    c4.m2, c5.m2, c6.m2, c7.m2, p12, c3.m0, c3.m3, c3.m5
  ];
  var s2 = [c7.m5, c8.m5, c9.m5, c10.m5, c7.m4, c8.m4, c9.m4, c10.m4,
    c7.m2, c8.m2, c9.m2, c10.m2, c3.m5, c3.m4, c3.m2, p15
  ];
  var s3 = [c0.m5, c0.m4, c0.m2, p3, c7.m0, c8.m0, c9.m0, c10.m0,
    c7.m3, c8.m3, c9.m3, c10.m3, c7.m5, c8.m5, c9.m5, c10.m5
  ];

  var m4 = s0[15];

  var n0 = normal(s0[0], s0[4], s0[8], s0[12], s0[13], s0[14], s0[15]);
  if (n0 == 0.0) {
    n0 = normal(s0[0], s0[4], s0[8], s0[12], s0[11], s0[7], s0[3]);
    if (n0 == 0.0) n0 = normal(s0[3], s0[2], s0[1], s0[0], s0[13], s0[14], s0[15]);
  }

  var n1 = normal(s1[12], s1[13], s1[14], s1[15], s1[11], s1[7], s1[3]);
  if (n1 == 0.0) {
    n1 = normal(s1[12], s1[13], s1[14], s1[15], s1[2], s1[1], s1[0]);
    if (n1 == 0.0) n1 = normal(s1[0], s1[4], s1[8], s1[12], s1[11], s1[7], s1[3]);
  }

  var n2 = normal(s2[15], s2[11], s2[7], s2[3], s2[2], s2[1], s2[0]);
  if (n2 == 0.0) {
    n2 = normal(s2[15], s2[11], s2[7], s2[3], s2[4], s2[8], s2[12]);
    if (n2 == 0.0) n2 = normal(s2[12], s2[13], s2[14], s2[15], s2[2], s2[1], s2[0]);
  }

  var n3 = normal(s3[3], s3[2], s3[1], s3[0], s3[4], s3[8], s3[12]);
  if (n3 == 0.0) {
    n3 = normal(s3[3], s3[2], s3[1], s3[0], s3[13], s3[14], s3[15]);
    if (n3 == 0.0) n3 = normal(s3[15], s3[11], s3[7], s3[3], s3[4], s3[8], s3[12]);
  }

  var n4 = normal(s2[3], s2[2], s2[1], m4, s2[4], s2[8], s2[12]);

  var m0, m1, m2, m3;

  // A kludge to remove subdivision cracks, only applied the first time
  // an edge is found to be flat before the rest of the subpatch is.
  if (flat0)
    m0 = [0.5 * (P0[0] + P1[0]), 0.5 * (P0[1] + P1[1]), 0.5 * (P0[2] + P1[2])];
  else {
    if ((flat0 = Distance1(p0, p[4], p[8], p12) < res2)) {
      var u = s0[12];
      var v = s2[3];
      var e = unit([u[0] - v[0], u[1] - v[1], u[2] - v[2]]);
      m0 = [0.5 * (P0[0] + P1[0]) + Epsilon * e[0], 0.5 * (P0[1] + P1[1]) + Epsilon * e[1],
        0.5 * (P0[2] + P1[2]) + Epsilon * e[2]
      ];
    } else
      m0 = s0[12];
  }

  if (flat1)
    m1 = [0.5 * (P1[0] + P2[0]), 0.5 * (P1[1] + P2[1]), 0.5 * (P1[2] + P2[2])];
  else {
    if ((flat1 = Distance1(p12, p[13], p[14], p15) < res2)) {
      var u = s1[15];
      var v = s3[0];
      var e = unit([u[0] - v[0], u[1] - v[1], u[2] - v[2]]);
      m1 = [0.5 * (P1[0] + P2[0]) + Epsilon * e[0], 0.5 * (P1[1] + P2[1]) + Epsilon * e[1],
        0.5 * (P1[2] + P2[2]) + Epsilon * e[2]
      ];
    } else
      m1 = s1[15];
  }

  if (flat2)
    m2 = [0.5 * (P2[0] + P3[0]), 0.5 * (P2[1] + P3[1]), 0.5 * (P2[2] + P3[2])];
  else {
    if ((flat2 = Distance1(p15, p[11], p[7], p3) < res2)) {
      var u = s2[3];
      var v = s0[12];
      var e = unit([u[0] - v[0], u[1] - v[1], u[2] - v[2]]);
      m2 = [0.5 * (P2[0] + P3[0]) + Epsilon * e[0], 0.5 * (P2[1] + P3[1]) + Epsilon * e[1],
        0.5 * (P2[2] + P3[2]) + Epsilon * e[2]
      ];
    } else
      m2 = s2[3];
  }

  if (flat3)
    m3 = [0.5 * (P3[0] + P0[0]), 0.5 * (P3[1] + P0[1]), 0.5 * (P3[2] + P0[2])];
  else {
    if ((flat3 = Distance1(p3, p[2], p[1], p0) < res2)) {
      var u = s3[0];
      var v = s1[15];
      var e = unit([u[0] - v[0], u[1] - v[1], u[2] - v[2]]);
      m3 = [0.5 * (P3[0] + P0[0]) + Epsilon * e[0],
        0.5 * (P3[1] + P0[1]) + Epsilon * e[1],
        0.5 * (P3[2] + P0[2]) + Epsilon * e[2]
      ];
    } else
      m3 = s3[0];
  }

  //  document.write(n0);      
  //  document.write(" < br > ");

  {
    /*
          var c0=new Array(4);
          var c1=new Array(4);
          var c2=new Array(4);
          var c3=new Array(4);
          var c4=new Array(4);
          
          for(var i=0; i < 4; ++i) {
          c0[i]=0.5*(C0[i]+C1[i]);
          c1[i]=0.5*(C1[i]+C2[i]);
          c2[i]=0.5*(C2[i]+C3[i]);
          c3[i]=0.5*(C3[i]+C0[i]);
          c4[i]=0.5*(c0[i]+c2[i]);
          }
       */

    var c0 = color(n0);
    var c1 = color(n1);
    var c2 = color(n2);
    var c3 = color(n3);
    var c4 = color(n4);


    var i0 = vertex(m0, c0, n0);
    var i1 = vertex(m1, c1, n1);
    var i2 = vertex(m2, c2, n2);
    var i3 = vertex(m3, c3, n3);
    var i4 = vertex(m4, c4, n4);

    render(s0, I0, i0, i4, i3, P0, m0, m4, m3, flat0, false, false, flat3,
      C0, c0, c4, c3);
    render(s1, i0, I1, i1, i4, m0, P1, m1, m4, flat0, flat1, false, false,
      c0, C1, c1, c4);
    render(s2, i4, i1, I2, i2, m4, m1, P2, m2, false, flat1, flat2, false,
      c4, c1, C2, c2);
    render(s3, i3, i4, i2, I3, m3, m4, m2, P3, false, false, flat2, flat3,
      c3, c4, c2, C3);
  }
}

var p;

function draw() {
  sceneSetup();
  // mat4.translate(mMatrix,mMatrix,[-0.5,-0.5,-1.5]);

  setBuffer();
  var p0 = p[0];
  var p3 = p[3];
  var p12 = p[12];
  var p15 = p[15];

  epsilon = 0;
  for (var i = 1; i < 16; ++i)
    epsilon = Math.max(epsilon,
      abs2([p[i][0] - p0[0], p[i][1] - p0[1], p[i][2] - p0[2]]));
  epsilon *= Fuzz2;

  var n0 = normal(p3, p[2], p[1], p0, p[4], p[8], p12);
  var n1 = normal(p0, p[4], p[8], p12, p[13], p[14], p15);
  var n2 = normal(p12, p[13], p[14], p15, p[11], p[7], p3);
  var n3 = normal(p15, p[11], p[7], p3, p[2], p[1], p0);

  var c0 = color(n0);
  var c1 = color(n1);
  var c2 = color(n2);
  var c3 = color(n3);

  var i0 = vertex(p0, c0, n0);
  var i1 = vertex(p12, c1, n1);
  var i2 = vertex(p15, c2, n2);
  var i3 = vertex(p3, c3, n3);

  render(p, i0, i1, i2, i3, p0, p12, p15, p3, false, false, false, false,
    c0, c1, c2, c3);
  drawBuffer();
}

var forceredraw = false;
var lasttime;
var newtime;
 
function tick() {
  requestAnimationFrame(tick);
  lasttime = newtime;
  newtime = performance.now();
  // invariant: every time this loop is called, lasttime stores the
  // last time processloop was called. 
  processloop(newtime - lasttime);
  draw();
}

function tickNoRedraw() {
  requestAnimationFrame(tickNoRedraw);
  if (redraw) {
    draw();
    redraw = false;
  }
}

function webGLStart() {
  var canvas = document.getElementById("Asymptote");
  initGL(canvas);
  initShaders();
  gl.clearColor(0.0, 0.0, 0.0, 1.0);
  gl.enable(gl.DEPTH_TEST);

  canvas.onmousedown = handleMouseDown;
  document.onmouseup = handleMouseUpOrTouchEnd;
  document.onmousemove = handleMouseMove;
  canvas.onkeydown = handleKey;
  document.onwheel = handleMouseWheel;

  canvas.addEventListener("touchstart", handleTouchStart, false);
  canvas.addEventListener("touchend", handleMouseUpOrTouchEnd, false);
  canvas.addEventListener("touchcancel", handleMouseUpOrTouchEnd, false);
  canvas.addEventListener("touchleave", handleMouseUpOrTouchEnd, false);
  canvas.addEventListener("touchmove", handleTouchMove, false);

  newtime = performance.now();

  if (forceredraw) {
  tick();
  } else {
    tickNoRedraw();
  }
}