code: function( x, y, w, h ){
      this._dat[ 0|VIEWPORT_X ] = x;
      this._dat[ 0|VIEWPORT_Y ] = y;
      this._dat[ 0|VIEWPORT_W ] = w;
      this._dat[ 0|VIEWPORT_H ] = h;
      this._set |= VIEWPORT_SET|0;
      return this;
    }
docs: VIEWPORT --------