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I am trying to change the size of the window of my app with:

    mysurface = SDL_SetVideoMode(width, height, 32, SDL_OPENGL);

Although I am using vsync swapbuffers (in driver xorg-video-ati), I can see flickering when the window size changes (I guess one or more black frames):

    void Video::draw()
{
    if (videoChanged){
        mysurface = SDL_SetVideoMode(width, height, 32, SDL_OPENGL);
        scene->init(); //Update glFrustum & glViewPort
    }
    scene->draw();
    SDL_GL_SwapBuffers();
}

So please, someone knows, if...
The SDL_SetVideoMode is not vsync'ed as is SDL_GL_SwapBuffers()?
Or is it destroying the window and creating another and the buffer is black in meantime?
Someone knows a working code to do this? Maybe in freeglut?

genpfault
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Weber K.
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1 Answers1

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In SDL-1 when you're using a windowed video mode the window is completely torn down and a new one created when changing the video mode. Of course there's some undefined data inbetween, which is perceived as flicker. This issue has been addressed in SDL-2. Either use that or use a different OpenGL framework, that resizes windows without gong a full window recreation.

If you're using a FULLSCREEN video mode then something different happens additionally:

A change of the video mode actually changes the video signal timings going from the graphics card to the display. After such a change the display has to find synchronization with the new settings and that takes some time. This of course comes with some flickering as the display may try to display a frame of different timings with the old settings until it detects that those no longer match. It's a physical effect and there's nothing you can do in software to fix this, other than not changing the video mode at all.

datenwolf
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  • I tried SDL2 and the flickering remained... But I now think the flickering is a Xorg feature or a radeon feature... I looked for the glxgears source code and when a resize occurs a redraw is made immediately... So the fps keeps vsync'ed but the flickering occurs, what I cant understand... :( – Weber K. Oct 04 '13 at 22:07
  • Maybe this is causing flickering in a lot a programs, including mine: background-pixmap -> "the server automatically tiles the regions with the window's background unless the window has a background of None." – Weber K. Oct 04 '13 at 23:22
  • I removed the background pixel from glxgears and chaged background pixmap to None. Now glxgears dont have flickering. But my SDL windows still have. Ill ask another question if I can disable this. Thank you very much! – Weber K. Oct 05 '13 at 02:22