# File gtk/sample/gtk-demo/pixbufs.rb, line 108
    def expose_cb(widget, event)
      rowstride = @frame.rowstride

      pixels = @frame.pixels
      pixels[0, rowstride * event.area.y + event.area.x * 3] = ''

      Gdk::RGB.draw_rgb_image(widget.window,
                              widget.style.black_gc,
                              event.area.x, event.area.y,
                              event.area.width, event.area.height,
                              Gdk::RGB::Dither::NORMAL,
                              pixels, rowstride,
                              event.area.x, event.area.y)
      true
    end