text: // cuon-matrix.js (c) 2012 kanda and matsuda
  /**
   * This is a class treating 4x4 matrix.
   * This class contains the function that is equivalent to OpenGL matrix stack.
   * The matrix after conversion is calculated by multiplying a conversion matrix from the right.
   * The matrix is replaced by the calculated result.
   */
  
  class Vector3 {
    constructor(opt_src) {
      var v = new Float32Array(3);
      if (opt_src && typeof opt_src === 'object') {
        v[0] = opt_src[0];
        v[1] = opt_src[1];
        v[2] = opt_src[2];
      }
      this.elements = v;
    }
  
    /**
     * Copy vector.
     * @param src source vector
     * @return this
     */
    set(src) {
      var i, s, d;
  
      d = this.elements;
  
      if (Array.isArray(src)) {
        s = src;
      } else {
        s = src.elements;
      }
  
      if (s === d) {
        return;
      }
  
      for (i = 0; i < 3; ++i) {
        d[i] = s[i];
      }
  
      return this;
    }
  
    /**
     * Add other to this vector.
     * @return this
     */
    add(other) {
      for (var i = 0; i < 3; i++) {
        this.elements[i] += other.elements[i];
      }
  
      // Don't delete the return statement.
      return this;
    }
  
    /**
     * Subtract other from this vector.
     * @return this
     */
    sub(other) {
      for (var i = 0; i < 3; i++) {
        this.elements[i] -= other.elements[i];
      }
  
      // Don't delete the return statement.
      return this;
    }
  
    /**
     * Divide this vector by a scalar.
     * @return this
     */
    div(scalar) {
      for (var i = 0; i < 3; i++) {
        this.elements[i] /= scalar;
      }
  
      // Don't delete the return statement.
      return this;
    }
  
    /**
     * Multiply this vector by a scalar.
     * @return this
     */
    mul(scalar) {
      for (var i = 0; i < 3; i++) {
        this.elements[i] *= scalar;
      }
  
      // Don't delete the return statement.
      return this;
    }
  
    /**
     * Calcualte the dop product between this vector and other.
     * @return scalar
     */
    static dot(other1, other2) {
      let d = 0;
  
      for (var i = 0; i < 3; i++) {
        d += other1.elements[i] * other2.elements[i];
      }
  
      // Don't delete the return statement.
      return d;
    }
  
    /**
     * Calcualte the cross product between this vector and other.
     * @return new vector
     */
    static cross(other1, other2) {
      let a = other1.elements;
      let b = other2.elements;
  
      let i = a[1] * b[2] - a[2] * b[1];
      let j = -1 * (a[0] * b[2] - a[2] * b[0]);
      let k = a[0] * b[1] - a[1] * b[0];
  
      let v3 = new Vector3([i, j, k]); // Modify this line to calculate cross product between other1 and other2.
  
      // Don't delete the return statement.
      return v3;
    }
  
    /**
     * Calculate the magnitude (or length) of this vector.
     * @return scalar
     */
    magnitude() {
      // Insert your code here.
      let m = 0; // Modify this line to calculate this vector's magnitude.
  
      for (var i = 0; i < 3; i++) {
        m += this.elements[i] * this.elements[i];
      }
  
      m = Math.sqrt(m);
  
      // Don't delete the return statement.
      return m;
    }
  
    /**
     * Normalize this vector.
     * @return this
     */
    normalize() {
      this.div(this.magnitude());
  
      // Don't delete the return statement.
      return this;
    }
  }
  
  class Vector4 {
    /**
     * Constructor of Vector4
     * If opt_src is specified, new vector is initialized by opt_src.
     * @param opt_src source vector(option)
     */
    constructor(opt_src) {
      var v = new Float32Array(4);
      if (opt_src && typeof opt_src === 'object') {
        v[0] = opt_src[0];
        v[1] = opt_src[1];
        v[2] = opt_src[2];
        v[3] = opt_src[3];
      }
      this.elements = v;
    }
  }
  
  class Matrix4 {
    /**
     * Constructor of Matrix4
     * If opt_src is specified, new matrix is initialized by opt_src.
     * Otherwise, new matrix is initialized by identity matrix.
     * @param opt_src source matrix(option)
     */
    constructor(opt_src) {
      var i, s, d;
      if (
        opt_src &&
        typeof opt_src === 'object' &&
        opt_src.hasOwnProperty('elements')
      ) {
        s = opt_src.elements;
        d = new Float32Array(16);
        for (i = 0; i < 16; ++i) {
          d[i] = s[i];
        }
        this.elements = d;
      } else {
        this.elements = new Float32Array([
          1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1,
        ]);
      }
    }
  
    /**
     * Set the identity matrix.
     * @return this
     */
    setIdentity() {
      var e = this.elements;
      e[0] = 1;
      e[4] = 0;
      e[8] = 0;
      e[12] = 0;
      e[1] = 0;
      e[5] = 1;
      e[9] = 0;
      e[13] = 0;
      e[2] = 0;
      e[6] = 0;
      e[10] = 1;
      e[14] = 0;
      e[3] = 0;
      e[7] = 0;
      e[11] = 0;
      e[15] = 1;
      return this;
    }
  
    /**
     * Copy matrix.
     * @param src source matrix
     * @return this
     */
    set(src) {
      var i, s, d;
  
      s = src.elements;
      d = this.elements;
  
      if (s === d) {
        return;
      }
  
      for (i = 0; i < 16; ++i) {
        d[i] = s[i];
      }
  
      return this;
    }
  
    /**
     * Multiply the matrix from the right.
     * @param other The multiply matrix
     * @return this
     */
    multiply(other) {
      var i, e, a, b, ai0, ai1, ai2, ai3;
  
      // Calculate e = a * b
      e = this.elements;
      a = this.elements;
      b = other.elements;
  
      // If e equals b, copy b to temporary matrix.
      if (e === b) {
        b = new Float32Array(16);
        for (i = 0; i < 16; ++i) {
          b[i] = e[i];
        }
      }
  
      for (i = 0; i < 4; i++) {
        ai0 = a[i];
        ai1 = a[i + 4];
        ai2 = a[i + 8];
        ai3 = a[i + 12];
        e[i] = ai0 * b[0] + ai1 * b[1] + ai2 * b[2] + ai3 * b[3];
        e[i + 4] = ai0 * b[4] + ai1 * b[5] + ai2 * b[6] + ai3 * b[7];
        e[i + 8] = ai0 * b[8] + ai1 * b[9] + ai2 * b[10] + ai3 * b[11];
        e[i + 12] = ai0 * b[12] + ai1 * b[13] + ai2 * b[14] + ai3 * b[15];
      }
  
      return this;
    }
  
    concat(other) {
      return this.multiply(other);
    }
  
    /**
     * Multiply the three-dimensional vector.
     * @param pos  The multiply vector
     * @return The result of multiplication(Float32Array)
     */
    multiplyVector3(pos) {
      var e = this.elements;
      var p = pos.elements;
      var v = new Vector3();
      var result = v.elements;
  
      result[0] = p[0] * e[0] + p[1] * e[4] + p[2] * e[8] + e[12];
      result[1] = p[0] * e[1] + p[1] * e[5] + p[2] * e[9] + e[13];
      result[2] = p[0] * e[2] + p[1] * e[6] + p[2] * e[10] + e[14];
  
      return v;
    }
  
    /**
     * Multiply the four-dimensional vector.
     * @param pos  The multiply vector
     * @return The result of multiplication(Float32Array)
     */
    multiplyVector4(pos) {
      var e = this.elements;
      var p = pos.elements;
      var v = new Vector4();
      var result = v.elements;
  
      result[0] = p[0] * e[0] + p[1] * e[4] + p[2] * e[8] + p[3] * e[12];
      result[1] = p[0] * e[1] + p[1] * e[5] + p[2] * e[9] + p[3] * e[13];
      result[2] = p[0] * e[2] + p[1] * e[6] + p[2] * e[10] + p[3] * e[14];
      result[3] = p[0] * e[3] + p[1] * e[7] + p[2] * e[11] + p[3] * e[15];
  
      return v;
    }
  
    /**
     * Transpose the matrix.
     * @return this
     */
    transpose() {
      var e, t;
  
      e = this.elements;
  
      t = e[1];
      e[1] = e[4];
      e[4] = t;
      t = e[2];
      e[2] = e[8];
      e[8] = t;
      t = e[3];
      e[3] = e[12];
      e[12] = t;
      t = e[6];
      e[6] = e[9];
      e[9] = t;
      t = e[7];
      e[7] = e[13];
      e[13] = t;
      t = e[11];
      e[11] = e[14];
      e[14] = t;
  
      return this;
    }
  
    /**
     * Calculate the inverse matrix of specified matrix, and set to this.
     * @param other The source matrix
     * @return this
     */
    setInverseOf(other) {
      var i, s, d, inv, det;
  
      s = other.elements;
      d = this.elements;
      inv = new Float32Array(16);
  
      inv[0] =
        s[5] * s[10] * s[15] -
        s[5] * s[11] * s[14] -
        s[9] * s[6] * s[15] +
        s[9] * s[7] * s[14] +
        s[13] * s[6] * s[11] -
        s[13] * s[7] * s[10];
      inv[4] =
        -s[4] * s[10] * s[15] +
        s[4] * s[11] * s[14] +
        s[8] * s[6] * s[15] -
        s[8] * s[7] * s[14] -
        s[12] * s[6] * s[11] +
        s[12] * s[7] * s[10];
      inv[8] =
        s[4] * s[9] * s[15] -
        s[4] * s[11] * s[13] -
        s[8] * s[5] * s[15] +
        s[8] * s[7] * s[13] +
        s[12] * s[5] * s[11] -
        s[12] * s[7] * s[9];
      inv[12] =
        -s[4] * s[9] * s[14] +
        s[4] * s[10] * s[13] +
        s[8] * s[5] * s[14] -
        s[8] * s[6] * s[13] -
        s[12] * s[5] * s[10] +
        s[12] * s[6] * s[9];
  
      inv[1] =
        -s[1] * s[10] * s[15] +
        s[1] * s[11] * s[14] +
        s[9] * s[2] * s[15] -
        s[9] * s[3] * s[14] -
        s[13] * s[2] * s[11] +
        s[13] * s[3] * s[10];
      inv[5] =
        s[0] * s[10] * s[15] -
        s[0] * s[11] * s[14] -
        s[8] * s[2] * s[15] +
        s[8] * s[3] * s[14] +
        s[12] * s[2] * s[11] -
        s[12] * s[3] * s[10];
      inv[9] =
        -s[0] * s[9] * s[15] +
        s[0] * s[11] * s[13] +
        s[8] * s[1] * s[15] -
        s[8] * s[3] * s[13] -
        s[12] * s[1] * s[11] +
        s[12] * s[3] * s[9];
      inv[13] =
        s[0] * s[9] * s[14] -
        s[0] * s[10] * s[13] -
        s[8] * s[1] * s[14] +
        s[8] * s[2] * s[13] +
        s[12] * s[1] * s[10] -
        s[12] * s[2] * s[9];
  
      inv[2] =
        s[1] * s[6] * s[15] -
        s[1] * s[7] * s[14] -
        s[5] * s[2] * s[15] +
        s[5] * s[3] * s[14] +
        s[13] * s[2] * s[7] -
        s[13] * s[3] * s[6];
      inv[6] =
        -s[0] * s[6] * s[15] +
        s[0] * s[7] * s[14] +
        s[4] * s[2] * s[15] -
        s[4] * s[3] * s[14] -
        s[12] * s[2] * s[7] +
        s[12] * s[3] * s[6];
      inv[10] =
        s[0] * s[5] * s[15] -
        s[0] * s[7] * s[13] -
        s[4] * s[1] * s[15] +
        s[4] * s[3] * s[13] +
        s[12] * s[1] * s[7] -
        s[12] * s[3] * s[5];
      inv[14] =
        -s[0] * s[5] * s[14] +
        s[0] * s[6] * s[13] +
        s[4] * s[1] * s[14] -
        s[4] * s[2] * s[13] -
        s[12] * s[1] * s[6] +
        s[12] * s[2] * s[5];
  
      inv[3] =
        -s[1] * s[6] * s[11] +
        s[1] * s[7] * s[10] +
        s[5] * s[2] * s[11] -
        s[5] * s[3] * s[10] -
        s[9] * s[2] * s[7] +
        s[9] * s[3] * s[6];
      inv[7] =
        s[0] * s[6] * s[11] -
        s[0] * s[7] * s[10] -
        s[4] * s[2] * s[11] +
        s[4] * s[3] * s[10] +
        s[8] * s[2] * s[7] -
        s[8] * s[3] * s[6];
      inv[11] =
        -s[0] * s[5] * s[11] +
        s[0] * s[7] * s[9] +
        s[4] * s[1] * s[11] -
        s[4] * s[3] * s[9] -
        s[8] * s[1] * s[7] +
        s[8] * s[3] * s[5];
      inv[15] =
        s[0] * s[5] * s[10] -
        s[0] * s[6] * s[9] -
        s[4] * s[1] * s[10] +
        s[4] * s[2] * s[9] +
        s[8] * s[1] * s[6] -
        s[8] * s[2] * s[5];
  
      det = s[0] * inv[0] + s[1] * inv[4] + s[2] * inv[8] + s[3] * inv[12];
      if (det === 0) {
        return this;
      }
  
      det = 1 / det;
      for (i = 0; i < 16; i++) {
        d[i] = inv[i] * det;
      }
  
      return this;
    }
  
    /**
     * Calculate the inverse matrix of this, and set to this.
     * @return this
     */
    invert() {
      return this.setInverseOf(this);
    }
  
    /**
     * Set the orthographic projection matrix.
     * @param left The coordinate of the left of clipping plane.
     * @param right The coordinate of the right of clipping plane.
     * @param bottom The coordinate of the bottom of clipping plane.
     * @param top The coordinate of the top top clipping plane.
     * @param near The distances to the nearer depth clipping plane. This value is minus if the plane is to be behind the viewer.
     * @param far The distances to the farther depth clipping plane. This value is minus if the plane is to be behind the viewer.
     * @return this
     */
    setOrtho(left, right, bottom, top, near, far) {
      var e, rw, rh, rd;
  
      if (left === right || bottom === top || near === far) {
        throw 'null frustum';
      }
  
      rw = 1 / (right - left);
      rh = 1 / (top - bottom);
      rd = 1 / (far - near);
  
      e = this.elements;
  
      e[0] = 2 * rw;
      e[1] = 0;
      e[2] = 0;
      e[3] = 0;
  
      e[4] = 0;
      e[5] = 2 * rh;
      e[6] = 0;
      e[7] = 0;
  
      e[8] = 0;
      e[9] = 0;
      e[10] = -2 * rd;
      e[11] = 0;
  
      e[12] = -(right + left) * rw;
      e[13] = -(top + bottom) * rh;
      e[14] = -(far + near) * rd;
      e[15] = 1;
  
      return this;
    }
  
    /**
     * Multiply the orthographic projection matrix from the right.
     * @param left The coordinate of the left of clipping plane.
     * @param right The coordinate of the right of clipping plane.
     * @param bottom The coordinate of the bottom of clipping plane.
     * @param top The coordinate of the top top clipping plane.
     * @param near The distances to the nearer depth clipping plane. This value is minus if the plane is to be behind the viewer.
     * @param far The distances to the farther depth clipping plane. This value is minus if the plane is to be behind the viewer.
     * @return this
     */
    ortho(left, right, bottom, top, near, far) {
      return this.concat(
        new Matrix4().setOrtho(left, right, bottom, top, near, far)
      );
    }
  
    /**
     * Set the perspective projection matrix.
     * @param left The coordinate of the left of clipping plane.
     * @param right The coordinate of the right of clipping plane.
     * @param bottom The coordinate of the bottom of clipping plane.
     * @param top The coordinate of the top top clipping plane.
     * @param near The distances to the nearer depth clipping plane. This value must be plus value.
     * @param far The distances to the farther depth clipping plane. This value must be plus value.
     * @return this
     */
    setFrustum(left, right, bottom, top, near, far) {
      var e, rw, rh, rd;
  
      if (left === right || top === bottom || near === far) {
        throw 'null frustum';
      }
      if (near <= 0) {
        throw 'near <= 0';
      }
      if (far <= 0) {
        throw 'far <= 0';
      }
  
      rw = 1 / (right - left);
      rh = 1 / (top - bottom);
      rd = 1 / (far - near);
  
      e = this.elements;
  
      e[0] = 2 * near * rw;
      e[1] = 0;
      e[2] = 0;
      e[3] = 0;
  
      e[4] = 0;
      e[5] = 2 * near * rh;
      e[6] = 0;
      e[7] = 0;
  
      e[8] = (right + left) * rw;
      e[9] = (top + bottom) * rh;
      e[10] = -(far + near) * rd;
      e[11] = -1;
  
      e[12] = 0;
      e[13] = 0;
      e[14] = -2 * near * far * rd;
      e[15] = 0;
  
      return this;
    }
  
    /**
     * Multiply the perspective projection matrix from the right.
     * @param left The coordinate of the left of clipping plane.
     * @param right The coordinate of the right of clipping plane.
     * @param bottom The coordinate of the bottom of clipping plane.
     * @param top The coordinate of the top top clipping plane.
     * @param near The distances to the nearer depth clipping plane. This value must be plus value.
     * @param far The distances to the farther depth clipping plane. This value must be plus value.
     * @return this
     */
    frustum(left, right, bottom, top, near, far) {
      return this.concat(
        new Matrix4().setFrustum(left, right, bottom, top, near, far)
      );
    }
  
    /**
     * Set the perspective projection matrix by fovy and aspect.
     * @param fovy The angle between the upper and lower sides of the frustum.
     * @param aspect The aspect ratio of the frustum. (width/height)
     * @param near The distances to the nearer depth clipping plane. This value must be plus value.
     * @param far The distances to the farther depth clipping plane. This value must be plus value.
     * @return this
     */
    setPerspective(fovy, aspect, near, far) {
      var e, rd, s, ct;
  
      if (near === far || aspect === 0) {
        throw 'null frustum';
      }
      if (near <= 0) {
        throw 'near <= 0';
      }
      if (far <= 0) {
        throw 'far <= 0';
      }
  
      fovy = (Math.PI * fovy) / 180 / 2;
      s = Math.sin(fovy);
      if (s === 0) {
        throw 'null frustum';
      }
  
      rd = 1 / (far - near);
      ct = Math.cos(fovy) / s;
  
      e = this.elements;
  
      e[0] = ct / aspect;
      e[1] = 0;
      e[2] = 0;
      e[3] = 0;
  
      e[4] = 0;
      e[5] = ct;
      e[6] = 0;
      e[7] = 0;
  
      e[8] = 0;
      e[9] = 0;
      e[10] = -(far + near) * rd;
      e[11] = -1;
  
      e[12] = 0;
      e[13] = 0;
      e[14] = -2 * near * far * rd;
      e[15] = 0;
  
      return this;
    }
  
    /**
     * Multiply the perspective projection matrix from the right.
     * @param fovy The angle between the upper and lower sides of the frustum.
     * @param aspect The aspect ratio of the frustum. (width/height)
     * @param near The distances to the nearer depth clipping plane. This value must be plus value.
     * @param far The distances to the farther depth clipping plane. This value must be plus value.
     * @return this
     */
    perspective(fovy, aspect, near, far) {
      return this.concat(new Matrix4().setPerspective(fovy, aspect, near, far));
    }
  
    /**
     * Set the matrix for scaling.
     * @param x The scale factor along the X axis
     * @param y The scale factor along the Y axis
     * @param z The scale factor along the Z axis
     * @return this
     */
    setScale(x, y, z) {
      var e = this.elements;
      e[0] = x;
      e[4] = 0;
      e[8] = 0;
      e[12] = 0;
      e[1] = 0;
      e[5] = y;
      e[9] = 0;
      e[13] = 0;
      e[2] = 0;
      e[6] = 0;
      e[10] = z;
      e[14] = 0;
      e[3] = 0;
      e[7] = 0;
      e[11] = 0;
      e[15] = 1;
      return this;
    }
  
    /**
     * Multiply the matrix for scaling from the right.
     * @param x The scale factor along the X axis
     * @param y The scale factor along the Y axis
     * @param z The scale factor along the Z axis
     * @return this
     */
    scale(x, y, z) {
      var e = this.elements;
      e[0] *= x;
      e[4] *= y;
      e[8] *= z;
      e[1] *= x;
      e[5] *= y;
      e[9] *= z;
      e[2] *= x;
      e[6] *= y;
      e[10] *= z;
      e[3] *= x;
      e[7] *= y;
      e[11] *= z;
      return this;
    }
  
    /**
     * Set the matrix for translation.
     * @param x The X value of a translation.
     * @param y The Y value of a translation.
     * @param z The Z value of a translation.
     * @return this
     */
  
    setTranslate(x, y, z) {
      var e = this.elements;
      e[0] = 1;
      e[4] = 0;
      e[8] = 0;
      e[12] = x;
      e[1] = 0;
      e[5] = 1;
      e[9] = 0;
      e[13] = y;
      e[2] = 0;
      e[6] = 0;
      e[10] = 1;
      e[14] = z;
      e[3] = 0;
      e[7] = 0;
      e[11] = 0;
      e[15] = 1;
      return this;
    }
  
    /**
     * Multiply the matrix for translation from the right.
     * @param x The X value of a translation.
     * @param y The Y value of a translation.
     * @param z The Z value of a translation.
     * @return this
     */
    translate(x, y, z) {
      var e = this.elements;
      e[12] += e[0] * x + e[4] * y + e[8] * z;
      e[13] += e[1] * x + e[5] * y + e[9] * z;
      e[14] += e[2] * x + e[6] * y + e[10] * z;
      e[15] += e[3] * x + e[7] * y + e[11] * z;
      return this;
    }
  
    /**
     * Set the matrix for rotation.
     * The vector of rotation axis may not be normalized.
     * @param angle The angle of rotation (degrees)
     * @param x The X coordinate of vector of rotation axis.
     * @param y The Y coordinate of vector of rotation axis.
     * @param z The Z coordinate of vector of rotation axis.
     * @return this
     */
    setRotate(angle, x, y, z) {
      var e, s, c, len, rlen, nc, xy, yz, zx, xs, ys, zs;
  
      angle = (Math.PI * angle) / 180;
      e = this.elements;
  
      s = Math.sin(angle);
      c = Math.cos(angle);
  
      if (0 !== x && 0 === y && 0 === z) {
        // Rotation around X axis
        if (x < 0) {
          s = -s;
        }
        e[0] = 1;
        e[4] = 0;
        e[8] = 0;
        e[12] = 0;
        e[1] = 0;
        e[5] = c;
        e[9] = -s;
        e[13] = 0;
        e[2] = 0;
        e[6] = s;
        e[10] = c;
        e[14] = 0;
        e[3] = 0;
        e[7] = 0;
        e[11] = 0;
        e[15] = 1;
      } else if (0 === x && 0 !== y && 0 === z) {
        // Rotation around Y axis
        if (y < 0) {
          s = -s;
        }
        e[0] = c;
        e[4] = 0;
        e[8] = s;
        e[12] = 0;
        e[1] = 0;
        e[5] = 1;
        e[9] = 0;
        e[13] = 0;
        e[2] = -s;
        e[6] = 0;
        e[10] = c;
        e[14] = 0;
        e[3] = 0;
        e[7] = 0;
        e[11] = 0;
        e[15] = 1;
      } else if (0 === x && 0 === y && 0 !== z) {
        // Rotation around Z axis
        if (z < 0) {
          s = -s;
        }
        e[0] = c;
        e[4] = -s;
        e[8] = 0;
        e[12] = 0;
        e[1] = s;
        e[5] = c;
        e[9] = 0;
        e[13] = 0;
        e[2] = 0;
        e[6] = 0;
        e[10] = 1;
        e[14] = 0;
        e[3] = 0;
        e[7] = 0;
        e[11] = 0;
        e[15] = 1;
      } else {
        // Rotation around another axis
        len = Math.sqrt(x * x + y * y + z * z);
        if (len !== 1) {
          rlen = 1 / len;
          x *= rlen;
          y *= rlen;
          z *= rlen;
        }
        nc = 1 - c;
        xy = x * y;
        yz = y * z;
        zx = z * x;
        xs = x * s;
        ys = y * s;
        zs = z * s;
  
        e[0] = x * x * nc + c;
        e[1] = xy * nc + zs;
        e[2] = zx * nc - ys;
        e[3] = 0;
  
        e[4] = xy * nc - zs;
        e[5] = y * y * nc + c;
        e[6] = yz * nc + xs;
        e[7] = 0;
  
        e[8] = zx * nc + ys;
        e[9] = yz * nc - xs;
        e[10] = z * z * nc + c;
        e[11] = 0;
  
        e[12] = 0;
        e[13] = 0;
        e[14] = 0;
        e[15] = 1;
      }
  
      return this;
    }
  
    /**
     * Multiply the matrix for rotation from the right.
     * The vector of rotation axis may not be normalized.
     * @param angle The angle of rotation (degrees)
     * @param x The X coordinate of vector of rotation axis.
     * @param y The Y coordinate of vector of rotation axis.
     * @param z The Z coordinate of vector of rotation axis.
     * @return this
     */
    rotate = function (angle, x, y, z) {
      return this.concat(new Matrix4().setRotate(angle, x, y, z));
    };
  
    /**
     * Set the viewing matrix.
     * @param eyeX, eyeY, eyeZ The position of the eye point.
     * @param centerX, centerY, centerZ The position of the reference point.
     * @param upX, upY, upZ The direction of the up vector.
     * @return this
     */
    setLookAt(eyeX, eyeY, eyeZ, centerX, centerY, centerZ, upX, upY, upZ) {
      var e, fx, fy, fz, rlf, sx, sy, sz, rls, ux, uy, uz;
  
      fx = centerX - eyeX;
      fy = centerY - eyeY;
      fz = centerZ - eyeZ;
  
      // Normalize f.
      rlf = 1 / Math.sqrt(fx * fx + fy * fy + fz * fz);
      fx *= rlf;
      fy *= rlf;
      fz *= rlf;
  
      // Calculate cross product of f and up.
      sx = fy * upZ - fz * upY;
      sy = fz * upX - fx * upZ;
      sz = fx * upY - fy * upX;
  
      // Normalize s.
      rls = 1 / Math.sqrt(sx * sx + sy * sy + sz * sz);
      sx *= rls;
      sy *= rls;
      sz *= rls;
  
      // Calculate cross product of s and f.
      ux = sy * fz - sz * fy;
      uy = sz * fx - sx * fz;
      uz = sx * fy - sy * fx;
  
      // Set to this.
      e = this.elements;
      e[0] = sx;
      e[1] = ux;
      e[2] = -fx;
      e[3] = 0;
  
      e[4] = sy;
      e[5] = uy;
      e[6] = -fy;
      e[7] = 0;
  
      e[8] = sz;
      e[9] = uz;
      e[10] = -fz;
      e[11] = 0;
  
      e[12] = 0;
      e[13] = 0;
      e[14] = 0;
      e[15] = 1;
  
      // Translate.
      return this.translate(-eyeX, -eyeY, -eyeZ);
    }
  
    /**
     * Multiply the viewing matrix from the right.
     * @param eyeX, eyeY, eyeZ The position of the eye point.
     * @param centerX, centerY, centerZ The position of the reference point.
     * @param upX, upY, upZ The direction of the up vector.
     * @return this
     */
    lookAt(eyeX, eyeY, eyeZ, centerX, centerY, centerZ, upX, upY, upZ) {
      return this.concat(
        new Matrix4().setLookAt(
          eyeX,
          eyeY,
          eyeZ,
          centerX,
          centerY,
          centerZ,
          upX,
          upY,
          upZ
        )
      );
    }
  
    /**
     * Multiply the matrix for project vertex to plane from the right.
     * @param plane The array[A, B, C, D] of the equation of plane "Ax + By + Cz + D = 0".
     * @param light The array which stored coordinates of the light. if light[3]=0, treated as parallel light.
     * @return this
     */
    dropShadow(plane, light) {
      var mat = new Matrix4();
      var e = mat.elements;
  
      var dot =
        plane[0] * light[0] +
        plane[1] * light[1] +
        plane[2] * light[2] +
        plane[3] * light[3];
  
      e[0] = dot - light[0] * plane[0];
      e[1] = -light[1] * plane[0];
      e[2] = -light[2] * plane[0];
      e[3] = -light[3] * plane[0];
  
      e[4] = -light[0] * plane[1];
      e[5] = dot - light[1] * plane[1];
      e[6] = -light[2] * plane[1];
      e[7] = -light[3] * plane[1];
  
      e[8] = -light[0] * plane[2];
      e[9] = -light[1] * plane[2];
      e[10] = dot - light[2] * plane[2];
      e[11] = -light[3] * plane[2];
  
      e[12] = -light[0] * plane[3];
      e[13] = -light[1] * plane[3];
      e[14] = -light[2] * plane[3];
      e[15] = dot - light[3] * plane[3];
  
      return this.concat(mat);
    }
  
    /**
     * Multiply the matrix for project vertex to plane from the right.(Projected by parallel light.)
     * @param normX, normY, normZ The normal vector of the plane.(Not necessary to be normalized.)
     * @param planeX, planeY, planeZ The coordinate of arbitrary points on a plane.
     * @param lightX, lightY, lightZ The vector of the direction of light.(Not necessary to be normalized.)
     * @return this
     */
    dropShadowDirectionally = function (
      normX,
      normY,
      normZ,
      planeX,
      planeY,
      planeZ,
      lightX,
      lightY,
      lightZ
    ) {
      var a = planeX * normX + planeY * normY + planeZ * normZ;
      return this.dropShadow(
        [normX, normY, normZ, -a],
        [lightX, lightY, lightZ, 0]
      );
    };
  }
  
  export { Vector3, Vector4, Matrix4 };
  