Performance drop after drawing a line

[-=MadMan=-]

Hi.

I'm porting a crossplatform 2D library under OpenGL. And occured a strange problem.
Test application works fine. The scene is rendered properly, and CPU load is very small. But after drawing some antialiased lines using GL_LINES I encounter a strange effect: application runs perfect until some invisible polygons runs into rendered scene. At this moment CPU load is about 100% It holds until this elements are at the screen. As soon I move them into invisible space everything becomes normal.
All polygons are textured.
Does anyone knows the possible cause of this effect?

Thanks.
Daniel.

[yooyo]

Might be a driver problem. Post more details... OS, graphics card, driver version...

yooyo

[-=MadMan=-]

Oh, sorry.
I have a ATi Radeon 9500 pro.
Working under Fedora Core 3 Linux with XOrg XServer running on it.
Driver version is 6.8.0.
Daniel.

[zeckensack]

I've had some issues with mixing line smoothing and shaders (ARB_fp, ATI_fs) on this type of card, though it was never a performance problem. I don't know a proper solution to this, unfortunately. On these cards I use either shaders or line smoothing, but not both.

Does your renderer use shaders?
If it does, try disabling GL_LINE_SMOOTH and see if it brings performance back to normal.

[-=MadMan=-]

No. I'm not using shaders.
I'm using the same method as http://www.opengl.org/resources/tutorials/sig99/advanced99/notes/node120.html