code: function ortho(left, right, bottom, top, near, far, dst) {
    dst = dst || new MatType(16);
  
    dst[0]  = 2 / (right - left);
    dst[1]  = 0;
    dst[2]  = 0;
    dst[3]  = 0;
  
    dst[4]  = 0;
    dst[5]  = 2 / (top - bottom);
    dst[6]  = 0;
    dst[7]  = 0;
  
    dst[8]  = 0;
    dst[9]  = 0;
    dst[10] = 2 / (near - far);
    dst[11] = 0;
  
    dst[12] = (right + left) / (left - right);
    dst[13] = (top + bottom) / (bottom - top);
    dst[14] = (far + near) / (near - far);
    dst[15] = 1;
  
    return dst;
  }
docs: Computes a 4-by-4 othogonal transformation matrix given the left, right,
  bottom, and top dimensions of the near clipping plane as well as the
  near and far clipping plane distances.
  @param {number} left Left side of the near clipping plane viewport.
  @param {number} right Right side of the near clipping plane viewport.
  @param {number} bottom Bottom of the near clipping plane viewport.
  @param {number} top Top of the near clipping plane viewport.
  @param {number} near The depth (negative z coordinate)
  of the near clipping plane.
  @param {number} far The depth (negative z coordinate)
  of the far clipping plane.
  @param {module:twgl/m4.Mat4} [dst] Output matrix.
  @return {module:twgl/m4.Mat4} The perspective matrix.
  @memberOf module:twgl/m4