//
// getShader
//
// Loads a shader program by scouring the current document,
// looking for a script with the specified ID.
//
function getShader(gl, id) {
  var shaderScript = document.getElementById(id);
  
  // Didn't find an element with the specified ID; abort.
  
  if (!shaderScript) {
    return null;
  }
  
  // Walk through the source element's children, building the
  // shader source string.
  
  var theSource = "";
  var currentChild = shaderScript.firstChild;
  
  while(currentChild) {
    if (currentChild.nodeType == 3) {
      theSource += currentChild.textContent;
    }
    
    currentChild = currentChild.nextSibling;
  }
  
  // Now figure out what type of shader script we have,
  // based on its MIME type.
  
  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;  // Unknown shader type
  }
  
  // Send the source to the shader object
  
  gl.shaderSource(shader, theSource);
  
  // Compile the shader program
  
  gl.compileShader(shader);
  
  // See if it compiled successfully
  
  if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
    alert("An error occurred compiling the shaders: " + gl.getShaderInfoLog(shader));
    return null;
  }
  
  return shader;
}

//
// Matrix utility functions
//

var mvMatrix = Matrix.I(4);
function loadIdentity() {
  mvMatrix = Matrix.I(4);
}

function multMatrix(m) {
  mvMatrix = mvMatrix.x(m);
}

function mvTranslate(v) {
  multMatrix(Matrix.Translation($V([v[0], v[1], v[2]])).ensure4x4());
}

/*
var mvMatrixStack = [];
function mvPushMatrix(m) {
    if (m) {
        mvMatrixStack.push(m.dup());
        mvMatrix = m.dup();
    } else {
        mvMatrixStack.push(mvMatrix.dup());
    }
}

function mvPopMatrix() {
    if (!mvMatrixStack.length) {
        throw ("Can't pop an empty matrix stack.");
    }
    mvMatrix = mvMatrixStack.pop();

    return mvMatrix;
}
*/

function mvRotate(angle, v) {
    var inRadians = angle * Math.PI / 180.0;
    var m = Matrix.Rotation(inRadians, $V([v[0], v[1], v[2]])).ensure4x4();
    multMatrix(m);
}

//
// augment Sylvester some
//

Matrix.Translation = function (v)
{
  if (v.elements.length == 2) {
    var r = Matrix.I(3);
    r.elements[2][0] = v.elements[0];
    r.elements[2][1] = v.elements[1];
    return r;
  }

  if (v.elements.length == 3) {
    var r = Matrix.I(4);
    r.elements[0][3] = v.elements[0];
    r.elements[1][3] = v.elements[1];
    r.elements[2][3] = v.elements[2];
    return r;
  }

  throw "Invalid length for Translation";
}

Matrix.prototype.flatten = function ()
{
    var result = [];
    if (this.elements.length == 0)
        return [];


    for (var j = 0; j < this.elements[0].length; j++)
        for (var i = 0; i < this.elements.length; i++)
            result.push(this.elements[i][j]);
    return result;
}

Matrix.prototype.ensure4x4 = function()
{
    if (this.elements.length == 4 &&
        this.elements[0].length == 4)
        return this;

    if (this.elements.length > 4 ||
        this.elements[0].length > 4)
        return null;

    for (var i = 0; i < this.elements.length; i++) {
        for (var j = this.elements[i].length; j < 4; j++) {
            if (i == j)
                this.elements[i].push(1);
            else
                this.elements[i].push(0);
        }
    }

    for (var i = this.elements.length; i < 4; i++) {
        if (i == 0)
            this.elements.push([1, 0, 0, 0]);
        else if (i == 1)
            this.elements.push([0, 1, 0, 0]);
        else if (i == 2)
            this.elements.push([0, 0, 1, 0]);
        else if (i == 3)
            this.elements.push([0, 0, 0, 1]);
    }

    return this;
};

Matrix.prototype.make3x3 = function()
{
    if (this.elements.length != 4 ||
        this.elements[0].length != 4)
        return null;

    return Matrix.create([[this.elements[0][0], this.elements[0][1], this.elements[0][2]],
                          [this.elements[1][0], this.elements[1][1], this.elements[1][2]],
                          [this.elements[2][0], this.elements[2][1], this.elements[2][2]]]);
};

Vector.prototype.flatten = function ()
{
    return this.elements;
};

function mht(m) {
    var s = "";
    if (m.length == 16) {
        for (var i = 0; i < 4; i++) {
            s += "<span style='font-family: monospace'>[" + m[i*4+0].toFixed(4) + "," + m[i*4+1].toFixed(4) + "," + m[i*4+2].toFixed(4) + "," + m[i*4+3].toFixed(4) + "]</span><br>";
        }
    } else if (m.length == 9) {
        for (var i = 0; i < 3; i++) {
            s += "<span style='font-family: monospace'>[" + m[i*3+0].toFixed(4) + "," + m[i*3+1].toFixed(4) + "," + m[i*3+2].toFixed(4) + "]</font><br>";
        }
    } else {
        return m.toString();
    }
    return s;
}

//
// gluLookAt
//
function makeLookAt(ex, ey, ez,
                    cx, cy, cz,
                    ux, uy, uz)
{
    var eye = $V([ex, ey, ez]);
    var center = $V([cx, cy, cz]);
    var up = $V([ux, uy, uz]);

    var mag;

    var z = eye.subtract(center).toUnitVector();
    var x = up.cross(z).toUnitVector();
    var y = z.cross(x).toUnitVector();

    var m = $M([[x.e(1), x.e(2), x.e(3), 0],
                [y.e(1), y.e(2), y.e(3), 0],
                [z.e(1), z.e(2), z.e(3), 0],
                [0, 0, 0, 1]]);

    var t = $M([[1, 0, 0, -ex],
                [0, 1, 0, -ey],
                [0, 0, 1, -ez],
                [0, 0, 0, 1]]);
    return m.x(t);
}

//
// gluPerspective
//
function makePerspective(fovy, aspect, znear, zfar)
{
    var ymax = znear * Math.tan(fovy * Math.PI / 360.0);
    var ymin = -ymax;
    var xmin = ymin * aspect;
    var xmax = ymax * aspect;

    return makeFrustum(xmin, xmax, ymin, ymax, znear, zfar);
}

//
// glFrustum
//
function makeFrustum(left, right,
                     bottom, top,
                     znear, zfar)
{
    var X = 2*znear/(right-left);
    var Y = 2*znear/(top-bottom);
    var A = (right+left)/(right-left);
    var B = (top+bottom)/(top-bottom);
    var C = -(zfar+znear)/(zfar-znear);
    var D = -2*zfar*znear/(zfar-znear);

    return $M([[X, 0, A, 0],
               [0, Y, B, 0],
               [0, 0, C, D],
               [0, 0, -1, 0]]);
}

//
// glOrtho
//
function makeOrtho(left, right, bottom, top, znear, zfar)
{
    var tx = - (right + left) / (right - left);
    var ty = - (top + bottom) / (top - bottom);
    var tz = - (zfar + znear) / (zfar - znear);

    return $M([[2 / (right - left), 0, 0, tx],
           [0, 2 / (top - bottom), 0, ty],
           [0, 0, -2 / (zfar - znear), tz],
           [0, 0, 0, 1]]);
}

