When you tile, you are using more fillrate to texture your polygons. So there is bound to be a drop in performance.

quote:I thought the Radeon 9700Pro had like no problem rendering a few hundred thousand polygons a sec?

Try several million. Honestly though, what's wrong with 128 fps? 132k polygons a frame multiplied by 128 frames per second is about 17 million triangles a second. Hmm maybe you are right... My Radeon 8500 can get about 15 million a second with unoptimized code. With 300 fps you are rendering almost 40 million triangles a second . I had a similar problem where textures would kill performance. I ruled it down to a bug in the driver with larger batch sizes... I think you are probably texel limted, not fill rate limited. How many times do you tile the textures over the terrain, and what size are they?

[edited by - Raloth on October 9, 2003 11:36:39 PM]

this is overkill. I don''t know if you''re drawing the terrain from a birdviewpoint (in which case the entire terrain would be visible) or from down below (in which case you would have massive overdraw).

Image the first situtation. You have a screen resolution of 1280x1024 (or something similar). If you tile a 256x256 texture 256 time, you''d effectively get a texture of 65536x65536 pixels. This is approximately 5000 (!) times as big as your screen area. That is what your card is effectively drawing. Only it''s just referencing to the same part of memory everytime because of the tiling. Either tile less, or use smaller texture. The combination you are using now is overkill.

In the second situation, you are drawing the entire world, but not seeing it on the screen. In this case, the texture resolution and tiling combination might be correct, but there is no way you will see all your 132k polygons. I''m guessing you are overdrawing a lot. In this case the solution would be some kind of visual culling algorithm.

Basically your card can handle that many polygons, but not in combination with the high tiling of your texture. The advertized numbers are only reachable in very special, limited cases.

I''m no expert on this matter, so if I''m making a total dork of myself, please let me know.

yes you are right about culling being a fillrate problem.

So you have a gods viewpoint of the entire map. And the map is instead of a scanner do I understand? Or can you zoom out. Either way, if you need to tile that texture that often for the result to look good, it is too detailed a texture. Here's another calculation for you.

If you use mipmapping (which you are I believe), the GPU selects a level of mipmap that corresponds to the approximate size on screen.

Assuming all 256x256 tiles are visible, with each tile a 256x256 pixel texture:
So we have your 256x256 texture tiled acros the screen 256 times in two directions. Using the width of your screen 1280 means that each tile takes about 5 pixels on the screenwidth, and for ease of calculation also 5 pixels vertically. So your 256x256 texture is mipmapped to 128, 64, 32, 16, 8. The 5th level of mipmapping is used. To get the exact same visuals, you should be able to replace your 256x256 pixel texture with a 8x8 pixel texture.

I'm not sure if this would also have a large effect on framerate, but I'd be interested in seeing what this does to the framerate.

Could you try this out and post the results here?

If you are zooming in and out, and need the detail when at ground level, maybe you should try to fade out certain texture levels when zooming out. So when zoomed all the way out, you want need the most detailed texture. As you zoom in, gradually fade in that detailed texture, until at some certain viewpoint, you can see it all.

about your other question: why are mipmaps used. If you don't use them, the GPU will have to skrunch up your texture on the fly it the texture is not mapped one-on-one to the screen. Normally this skrunching is not optimal. By using mipmaps you can precalculate the skrunching, and you will have more time to do it (normally). Therefore, better algorithms can be used to generate a nicer result.
You can try it easily your self. Create a checkerboard image, and stick it onto a quad as in this picture (the right quad with perspective): http://www.cmlab.csie.ntu.edu.tw/~robin/JavaGL/Example-app/images/checker.gif . Now check the difference between using mipmaps or not using them (run it twice with different settings, or better make two quads and load the texture twice with different settings). If you make the quad bigger than no this picture, you should clearly see the better visual result of using mipmaps.

[edited by - rick_appleton on October 10, 2003 3:15:14 AM]