D2X-XL contains multi-threading code for a long time already, and it could significantly speed up rendering (for the vertex lighting path, that is). It had its share of problems though: Some tasks that I had multi threaded tended to lock up, and I could never figure why (debugging multiple threads is a daunting challenge to say the least). It didn't work at all for the new lightmap and per pixel render paths, and it also didn't help with a few very CPU intensive tasks, namely computing effects like smoke, lightnings and energy sparks.

I had done quite some experimentation during the past months, trying to put the renderer in a different thread and having the non-visual stuff run parallel to it, but first of all it was a pain in the neck to share the OpenGL render context between the main thread doing the 2D rendering for the menus, and the render thread displaying the mine, and secondly with a few exceptions the renderer consumed 95% of the entire frame time, so it wasn't worth it.

Still, this was rumouring in the back of my head, and sometimes such things are like wine: You need to let it rest and mature to be able to enjoy its full potential. So after letting the whole story rest and mature for a while there in the code cellar in the back of my head, I came to the conclusion that putting the effects code in a separate thread and having it run parallel to the renderer solved two problems at once: First of all, I didn't have to share render contexts any more, and secondly I could accelerate exactly that code that in extreme cases would slow the program tremendously down by executing it when the program did something very time consuming anyway already. So the main benefit of multi threading now will not be increasing frame rates in standard situations (sounds like I've been watching too much soccer lately ...), but prevent them from dropping as much as they did in very CPU intensive scenes.

In the course of doing that, I also salvaged of the existing multi threading code what had proved to be useful and stable, and so I can now present a new take at multi threading in D2X-XL that should really make multi core CPU owners happy. To round the package off, the multi tasking options menu has gotten an overhaul, offering a few meaningful options where the various multi threading blocks in the program can be separately turned on and off, be it for testing and speed comparison, or because one of them causes problems (which hopefully won't arise, as I have done a lot of testing and rearranging code to avoid data invalidation by competing threads).

Regard that you still need to enable multi threading by placing the switch '-multithreading 1' in d2x.ini.