Poor OpenGL performance?

[Murphy]

For some reason under Windows XP, the terrain demo runs at 60fps when I view the terrain and a lot more when I don't view it. This was in DirectX and OpenGL. Maybe my drivers are crap under Windows. Hmm.

Is your monitor refresh rate at 60Hz (remember if you're viewing full screen it may not be the same as your normal "desktop" refresh rate)? If it is, this makes sense -- in many cases you'll be limited to the actual refresh rate, since rendering at, say, 120 FPS on a screen with 60Hz refresh will result in half of the screen being one frame and the other half being the next frame. This behavior can usually be altered.

[Guest]

quote:
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Originally posted by Fred:
For some reason under Windows XP, the terrain demo runs at 60fps when I view the terrain and a lot more when I don't view it. This was in DirectX and OpenGL. Maybe my drivers are crap under Windows. Hmm.
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Fred;
There is no free ride in 3D graphics, and very little magic.
The engine has the job of reading the geometric data and
all logic state data, then presenting it to the screen ( aka front
buffer). If there is minimal data to read, then the program is
able to do this more times in a second. As the data increases,
the number of times this can occur in a second decreases. Each
video card has CAPS data associated with it. One of the CAPS is the
MaxPrimitiveCount , the maximum primitives the card can render.
As that count increases, the number of times the engine can complete
a cycle or frame decreases. To see this in action, create an empty
3D scene and observe the fps, then add terrain and several static
objects to the scene and maybe an animated character or two and
observe the fps.
It will take the computer longer to crunch the numbers and present
each frame, hence more work the longer it takes and the fewer times
it can do it each second. That's what GFXstyLER meant by pure logic.

[Priest]

Anyone even tried to explain the slow down when camera is looking to a large piece of terrain, as oposed to when looking to the oposite direction ?

I mean to explain it, using Irrlicht renderer logic( like octrees, AABBoxes , LOD system ), and not the human eye hertz resolution, monitor refresh rate, video card MaxPrimitiveCount etc.

I would expect almost twice 400fps when running the terrain demo - I get 600+fps when running other terrain demos.

I guess the other demos aren't sending vertex data from sys. mem to vid. mem every frame.

[Fred]

But 60fps for a terrain demo on an AMD64, with 1Gb and GeForce 2 GTS? That's terrible performance.

[Fred]

What I'm trying to say is that I get almost 800fps from the OGRE terrain demo under Linux at 800x600x32, whereas with the Irrlicht terrain demo under Linux I get 380fps at 800x600x32. I was trying to avoid bringing another engine into the conversation but the difference is striking.

And when I run the terrain demo under Windows, I get 60-110fps under DX9 and OpenGL when I move around the terrain

[Guest]

I get the same FPS working with jirr 0.4 under java debugging. I blame it to the debugging.

[Fred]

But 60fps for a terrain demo on an AMD64, with 1Gb and GeForce 2 GTS? That's terrible performance.

Oops, did I say GeForce 2 GTS? I meant I have a GeForce 6600GTS.