code: function (x, y, w, h) {
              this.gl.viewport(x, y, w, h);
          }
docs: Sets the viewport
  @name setViewport
  @memberOf me.WebGLRenderer.Compositor
  @function
  @param {Number} x x position of viewport
  @param {Number} y y position of viewport
  @param {Number} width width of viewport
  @param {Number} height height of viewport