function frustum(out, left, right, bottom, top, near, far) {
    var rl = 1 / (right - left);
    var tb = 1 / (top - bottom);
    var nf = 1 / (near - far);
    out[0] = near * 2 * rl;
    out[1] = 0;
    out[2] = 0;
    out[3] = 0;
    out[4] = 0;
    out[5] = near * 2 * tb;
    out[6] = 0;
    out[7] = 0;
    out[8] = (right + left) * rl;
    out[9] = (top + bottom) * tb;
    out[10] = (far + near) * nf;
    out[11] = -1;
    out[12] = 0;
    out[13] = 0;
    out[14] = far * near * 2 * nf;
    out[15] = 0;
    return out;
  }
Generates a frustum matrix with the given bounds

@param {mat4} out mat4 frustum matrix will be written into
@param {Number} left Left bound of the frustum
@param {Number} right Right bound of the frustum
@param {Number} bottom Bottom bound of the frustum
@param {Number} top Top bound of the frustum
@param {Number} near Near bound of the frustum
@param {Number} far Far bound of the frustum
@returns {mat4} out