Sunday, April 29, 2007

Turn Off "Draw Hi-Detailed World"

It looks so innocent, that one check box..."draw hi detailed world". What harm could it do?

Well, if you have a GeForce FX graphics card, quite a bit! If you have Vista it may not be a great idea either.

The "draw hi-detail world" setting turns on multiple rendering settings that look nice but hurts fps. There are two I can think of right now:
  • With the setting on, we draw 3-d structures for airport lights. This can slow down slower machines, but usually isn't the big problem.
  • With this setting on, we use pixel shaders to draw terrain - without it we use the traditional "fixed function" OpenGL pipeline.
It's this second behavior that causes all the misery. X-Plane won't use pixel shaders if your video card doesn't have them. But...what if your card has pixel shaders and they're just not very good?

I should say: I have no first-hand knowledge of how the GeForce FX series works, and what I am repeating is simply conjecture posted on the web, albeit conjecture that explains what we keep hearing from users. The GeForce FX (nVidia's first series of programmable pixel-shader based cards) is a hybrid card - half the card's transistors are dedicated to fixed-function drawing, and only half for shaders. Thus if we go into shader mode, we basically "lose" half the chip, and our performance tanks. (ATI built 100% programmable cards starting with their first entry, the 9700, and nVidia went this way with the 6000 series.)

So if you have an FX card, it tells X-Plane "I can do shaders". With "hi-detailed world" on, we take a huge performance hit. Simple solution for FX users: turn "hi-detailed world" off! Get your fps back!

I've also heard a bunch of reports that the new drivers for Vista have bugs...they seem to come out more when we use pixel shaders . Again - turn "hi detailed world" off and see if it helps!

Bottom line: "draw hi detailed world" is proving to be an aggressive setting - I recommend backing it down as the first step in trouble-shooting performance problems.

1 comment:

Anonymous said...

Hey Ben,

Thanks for doing these little Blogs. They are very informative, positively worth your time writing.

Blue side up,