* to do this efficiently the amount of required vertices needs to be calculated up-front
* always create the vertices in the data generation pass, not the render pass.
* added synchronisation code to the vertex buffer allocator.
Without multithreading this causes a slight slowdown, due to added processing cost. (Frozen Time bridge scene drops from 47 fps to 44 fps on my test machine.
This was done to clean up the license and to ensure that any commercial fork of the engine has to obey the far stricter requirements concerning source distribution. The old license was compatible with GPLv2 whereas combining GPLv2 and LGPLv3 force a license upgrade to GPLv3. The license of code that originates from ZDoomGL has not been changed.
It makes no sense having them organized differently in this struct than what the rendering code needs. This saves one redundant copy operation and a function-local static variable.
