I've seen the messages in Ters thread and indeed I am seeing similar problems. The performance of the first version was very bad, 200ms for a screen redraw, sometimes worse.
I can't measure exactly how much Simutrans simulation engine needs and how much the OpenGL backend needs, but on this netbook (Intel Celeron N3350, 4 GB RAM, Intel on board graphics HD500) I now get stable 25 FPS at a window size of 1000x750 pixels with pak64. There might be room for improvement, but I have taken care of the basic tricks like combining many tile images into one big texture so my code does not need to switch textures that often. I must see what I can do to make it better.
Loading the paks and converting the graphics is really slow with my current code though, so that will be my next thing to investigate. I clearly don't use the optimal method there.
Right now it's looking just the same as before, well, kinda, you see which parts I have not implemented yet. But with OpenGL it will be easier to add nice graphics gimmicks later.
I'm currently optimising my testing workflow, and thus wanted to start the game with my testing-pakset directly after compiling my testing folders. I ran into the issue of not being able to select my testing pakset, when placed in the usr/simutrans/paksets folder, compared to: https://www.simutrans-germany.com/wiki/wiki/en_start_parameter Would love to see this happening in future