ATI / NVIDIA Performance Issues

weasalmongler · 2005-07-19T16:14:18

Hi everyone, I recently upgraded my graphics card from an ATI Radeon 9800 Pro to a Geforce 6800 GT, and I have suddenly taken a big performance hit in my game. I was initially getting about 300 FPS with my ATI card, and now I am getting 90 - 100 FPS with the NVIDIA one. Basically I'm doing many of the optimisation techniques in DirectX, I am writing all my game objects to a dynamic buffer created with D3DUSAGE_DYNAMIC and D3DUSAGE_WRITEONLY, sorted by texture, so there is basically one vertex buffer going to Direct 3D for each texture in the game world. I am locking the Vertex Buffer with D3DLOCK_DISCARD as well. I'm also drawing everything as an Indexed Vertex Buffer. I perform frustum culling on the world objects to reduce some of them, and rendering front to back won't really make much difference, as I am making a space sim game. My method of batching by texture rather than distance from the player should give a much better speed increase. I'm not doing anything complicated with my rendering system yet. I'm using standard DirectX 9, not fiddling around with any Vertex or Pixel shaders. I basically just use textures, lighting and thats about it. So basically my question is, does anyone have any idea why there should be such a big difference between ATI and NVIDIA cards? In my experience, speed differences are usually minimal between similar powered cards, so why a faster card should render slower is a bit beyond me. Thanks for any help in advance, - James

Graphics and GPU Programming Programming

Started by weasalmongler July 18, 2005 06:18 PM

11 comments, last by weasalmongler 18 years, 9 months ago

ganchmaster

134

July 19, 2005 02:09 PM

Quote:Original post by weasalmongler
If I put them into a static buffer then I am unable to move them around. I would have to do one call to DrawIndexedPrimitive as I would have to change the modelview matrix. By performing the transformations myself on the CPU, I eliminate this problem.

I see. Like AndyTX said, it sounds like you need to look into instancing techniques, if you really want to draw a large number of independently moving objects with a single DrawPrim call. With the right instancing scheme, you should theoretically be able to make a good optimization by saving a lot of the overhead of the dynamic buffer.

But also, even if you are using a dynamic buffer, why are you calling CreateVertexBuffer every frame? You can create it once and fill it over and over. Maybe that is the source of your problems?

SimmerD

1,210

July 19, 2005 03:07 PM

You should never create a vb every frame. As Brian Fellows would say 'THAT's CRAZY!!'. ;)

Using a dynamic buffer itself shouldn't be a big hit, but creating index and/or vertex buffers each frame is a big hit - and there are no guarantees how long this might take.

Let me guess - you aren't sure how big the buffer needs to be b/c you don't know how many items will be in view?

If so, treat your dynamicvb as a staging area, and keep lock(), write, unlock() for each object, and then draw() when it's full or you need to change texture, or the frame is over. When you draw b/c it's full, you need to re-lock with discard and keep going.

Game Development Journal

weasalmongler

205

Author

July 19, 2005 04:14 PM

I just rewrote the way the program allocates the dynamic vertex buffer, so now we create a large one at the start of the program and deallocate at the end. Any time inbetween it is simply locked and unlocked to write data to it.

This has given me a huge performance enhancement. It has gone from pretty much a constant 70 - 100 FPS to an amazing 150 - 400 FPS with literally loads of enemies and other ships all over the place. I still have a bit of optimising to do but I think I can sort it now that I have established the cause of the problem.

Many thanks to everyone who helped with this issue.

- James

ATI / NVIDIA Performance Issues

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ATI / NVIDIA Performance Issues

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