BSP Entity Overdraw Optimizations Progress (Patreon)

Now things are getting interesting. This specific scene is going from 3 fps in Retroquad 0.17.1 to 11 fps in the current work-in-progress code. That's over 250 percent faster, enough to make this particular map playable.

There are some issues with alphamask ("fence") textured polygons not following their moving BSP entities, though. You can see how the floor of the elevator is on the top of the elevator's path while the elevator itself has not moved. And those lower fences weren't activated yet, so they weren't supposed to be visible.

After fixing this bug I'm going to do some more testing before releasing the next version.