1) First online interview using one of those Cisco-like online conference software, general questions about background, previous experiences etc.
2) First technical interview (online) using shared document, very basic C++ questions, nothing top worry about if you worked as C++ developer during last years (basic template, virtual function calls to figure out program output, a couple of questions about basic STL set etc.)
3) If they select you for next step, you will be invited for a local face to face interview. At the current writing, if you're not living int he same city they company will reimburse travel expenses. Office interview is very long, not difficult, you talk with your future colleagues, they explain/show you what they're working on, they might ask you some question about computer graphics, C++ etc. Friendly people anyway. You will also have online call from office with few managers in Texas, general questions and/or some technical ones about raytracing techniques.
The company is not actively looking for software developers, there might be an open position once a while in Vienna office, so few candidates are competing for the same position. Because they're working on visualization software, they give priority to those who had experience in that field I guess.