select a certain part of 2d visualization, switch to GCode view - it will highlight list of lines responsible for visualized piece)
In that case you will need to set it manually in 'Printer Info' tab All you need to do - is drag your *.gcode file to the designated zone.
GCodeViewer gCodeViewer is a visual GCode visualizer, viewer and analyzer in your own browser! It works on any OS in almost any modern browser (chrome, ff, safari 6, opera, ie10 should work too).