Strange LWJGL performances

[Chman]

Hello

While making some performance tests, I found something interesting :

When initializing a black opengl screen with LWJGL in 800x600x16, I get about 1000 fps.
When I just swith the display mode to 1024x768 I get 1300 fps...
Can someone explain me why ?

(my desktop is using a 1152x900 resolution, and my computer is an AMD 3000+)

Chman

[Java Cool Dude]

FullScreen mode will give you up to 100% more performance

[Chman]

I know
But the two tests run in fullscreen mode... The thing I don't understand is that the game run faster in 1024x768 than in 800x600...

Games published by our own members! Check 'em out!

[Orangy Tang]

When you're dealing with framerates that high, the actual time difference is *tiny*, and absolutly anything a computer does differently can cause an apparently huge fps difference. I wouldn't worry about it unless you actually notice a big difference in an actual game.

[cfmdobbie]

Are you using 16bpp in both cases?

Ignoring the obvious size difference, the main difference between 800x600 and 1024x768 is the fact that 800 and 600 don't relate in any way to "nice" power-of-2 numbers.  It's possible that the hardware or software has to do something ever so slightly differently to account for this, which takes it a tiny bit longer to do.  The difference you're seeing is only about 200ns, which given the testing environment (a home computer) could be considered a stastical error.

More interesting would be working out whether you're seeing a 30% or a 200ns increase in performance.  Draw a grid of 500 quads or something and see how the numbers come out then.

Edit: Given that 1024x768 is such a popular resolution, it's possible that the drivers have been slightly tuned to reflect this.  One more thing to think about!

[Chman]

Are you using 16bpp in both cases?

Yes

Anyways, thanks for all your answers !