Invert DXF (or another method?) for lasercut

[jago25_98]

I'm trying to achieve this:

Is my laser cutter software bad? Is the badly documented DXF file format the problem? Should I convert to a different revision of DXF?

 

In this image the slices are being cut the wrong way round. I need black on white:

 

Here's the import options in this laser cutter program:

 

Related thread:

http://www.eng-tips.com/viewthread.cfm?qid=306918

 

But how can I do this with a free CAD program such as QCAD or LibreCAD? Or something else?

 

Actual lasercut software:

http://www.triumphlaser.com/UploadFiles/Downloads/triumphlaser%207.02.zip

Example DXF:

[url="https://drive.google.com/file/d/0B0HQ4sTmMF_cYnROT0JHQk4wUWM/view?usp=sharing