There are two buttons to finally start the SPRAY ray-tracing simulation:

•Simulation: This starts the simulation and blocks all other windows of SPRAY until the computation has finished. You will see a progress bar indicating the percentage of the work that has been done already. This is the fastest and safest way to do simulations.

•Simulation (thread): The simulation is started in a separate thread. This way of doing the simulation is slower compared to the first one. During the computation, SPRAY will react to mouse clicks and other user actions. You can close or move windows and inspect object data. However, you should not change any parameters that may have influence on the simulation.