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Thread: glReadPixels gets an overlapping window

  1. #1
    Junior Member Newbie
    Join Date
    May 2002

    glReadPixels gets an overlapping window

    I am using glReadPixels to get a piece of frame buffer of my viewport. It returned with a partially overlapping window from other application. It happens on one of my graphics card(WildCat4110) but not others. I understand this is because glReadPixels implemented on the graphic card does not save those obscured areas to an offscreen buffer therefore glReadPixels cannot get a complete image of viewport. Does anyone know a way to query the gaphics card whether it supports offscreen buffer? Thanks

  2. #2
    Junior Member Newbie
    Join Date
    Mar 2002

    Re: glReadPixels gets an overlapping window

    I don't think there is what you are looking for. However I stongly believe may cad apps out there treat the pixel formats with PFD_SWAP_COPY that way. If you read the spec for this there is nothing that promises offscreen buffers, just that swap won't kill anything in the back buffer. But like I said many popular cad apps seem to treat this incorrectly.

    I figure cards that export this bit in their pixel format do it via offscreen buffers or they would show corruption in these apps. So I guess it's up to you as to whether you want to be wrong with them, or do things correctly.

  3. #3
    Member Regular Contributor
    Join Date
    Mar 2001

    Re: glReadPixels gets an overlapping window


    you should look for WGL_ARB_pbuffer or GLX_SGIX_pbuffer extensions. So you can render to an offscreen buffer without troubles.


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