Compatibility Settings questions

[Swirecfimer]

In the compatibility settings I have D3D9 BC4/5 and D3D9Ex on. But when I put it off, I get about 6 fps more (tested it on 1 map). The downsides are that the screen goes black after alt tabbing and the car feels less responsive even with more fps. So what does these 2 settings actually do?

Some other thing. What is Lightmap quality?

Thx for the help.

[TMarc]

D3D9Ex is a Extension of DirectX, some details here.

Lightmap quality is the default lightmap quality to use if the map you are loading has no or a less good lightmap quality than this setting.
Normally people calculate high or ultra lightmaps before publishing them, but that takes quite some time.