alpha blending istn't that slow. on my old gf 440 mx i got around 30 fps for an approximate 10x full-screen overdraw with additive alpha blending.

So, isn't that the problem causing low framerate for me?

I agree.

In my project (Pax et Bellum) I use thousands of grass models with alpha channel.
And I have no problem with the frame rate, because I use mipmaps and LOD.

That's right.
But if you use mipmaps, only the smaller mipmap must be rendered when an object is far away. Rendering/blending is much faster then.
In my game I use very detailed textures (8192 x 8192 pixels). To render them as fast as possible, I use DDS textures with 9(!) Mipmaps.

Here you can see a screenshot of my game with thousands of grass models (all with alpha channel). The frame rate is higher than 60 FPS even though the level is not finished and optimized now (the grass models in this test level are old models with only 4 Mipmaps, and I use no LOD).


(click here to see the original size of the screenshot)

Screens are great, you've done great job Harry Potter. May be I'll need to rewrite my project, so that way I could make it better or something...

When I am not wrong, than you misunderstood him.

The things he discribed are no scripts but changes on the sprites (LOD/MipMap)

Harry Potter: How do you handle sorting?

Rei_Ayanami, I've already done MipMaps with help of Harry Potter, I meant that may be I need to look more deeper into my problem.
And still, even Slin and others say that problem is with alpha thing, I don't believe that my PC can't draw 80 bushes!

As a quick test try this effect on your alpha stuff: http://www.opserver.de/wiki/index.php/ImprovedOverlay

Did, what was the point? Same fps, but still as I said earlier, fps problem isn't constant.

Yes.
When I do not use mipmapping, my game would run with less then 5 FPS. Because all my detailed textures will be rendered each frame. When using a texture size of 4096x4096 pixel (eg. a flat sqare model with a texture), the engine must draw 16777216 Pixels each frame for only ONE model.

So I use mipmaps to reduce the texture size of models that are far away. It's the same like LOD, but for textures.

For example: when you use a texture size of 4096x4096 pixel, then I use 8 Mipmaps for them.
The original texture has 4096x4096 pixels,
the 1st mipmap only 2048x2048 pixels,
the 2nd mipmap only 1024x1024 pixels,
the 3rd mipmap only 512x512 pixels,
...
mipmap number 8 will have a texture size of only 16x16 pixels. And this is rendered much faster than the original texture size of 4096x4096.