code: function pollViewport () {
      var viewport = nextState.viewport
      var scissorBox = nextState.scissor_box
      viewport[0] = viewport[1] = scissorBox[0] = scissorBox[1] = 0
      contextState.viewportWidth =
        contextState.framebufferWidth =
        contextState.drawingBufferWidth =
        viewport[2] =
        scissorBox[2] = gl.drawingBufferWidth
      contextState.viewportHeight =
        contextState.framebufferHeight =
        contextState.drawingBufferHeight =
        viewport[3] =
        scissorBox[3] = gl.drawingBufferHeight
    }
docs: poll viewport