XdbeGetVisualInfo(3X11)

NAME
       XdbeGetVisualInfo

SYNOPSIS
       #include <X11/extensions/Xdbe.h>

       XdbeScreenVisualInfo *XdbeGetVisualInfo(
           Display  *dpy,
           Drawable *screen_specifiers,
           int      *num_screens)

DESCRIPTION
       This function returns information about which visuals sup-
       port double buffering.  The argument num_screens specifies
       how many elements there are in the screen_specifiers list.
       Each drawable in screen_specifiers designates a screen for
       which  the  supported  visuals  are  being  requested.  If
       num_screens  is  zero,  information  for  all  screens  is
       requested.   In this case, upon return from this function,
       num_screens will be set to the number of screens that were
       found.   If  an  error occurs, this function returns NULL,
       else it returns a pointer to a list  of  XdbeScreenVisual-
       Info structures of length num_screens.  The nth element in
       the returned list corresponds to the nth drawable  in  the
       screen_specifiers  list,  unless num_screens was passed in
       with the value zero, in which case the nth element in  the
       returned list corresponds to the nth screen of the server,
       starting  with  screen  zero.   The   XdbeScreenVisualInfo
       structure has the following fields:

            int            count
            XdbeVisualInfo *visinfo

       count  specifies  the number of items in visinfo.  visinfo
       specifies a list of visuals, depths, and performance hints
       for this screen.

       The XdbeVisualInfo structure has the following fields:

            VisualID visual
            int      depth
            int      perflevel

       visual  specifies  one  visual  ID  that  supports double-
       buffering.  depth specifies the depth of the visual.  per-
       flevel is a performance hint.

       The only operation defined on a perflevel is comparison to
       a perflevel of another visual on  the  same  screen.   The
       visual  having the higher perflevel is likely to have bet-
       ter double-buffering graphics performance than the  visual
       having  the  lower perflevel.  Nothing can be deduced from
       the following: the magnitude of the difference of two per-
       flevels,  a  perflevel  value  in  isolation, or comparing

       perflevels from different servers.

ERRORS
       BadDrawable
              One or more values passed in  screen_specifiers  is
              not a valid drawable.

SEE ALSO
       DBE, XdbeAllocateBackBufferName() XdbeBeginIdiom() Xdbe- 
       DeallocateBackBufferName() XdbeEndIdiom() XdbeFreeVisu- 
       alInfo() XdbeGetBackBufferAttributes() XdbeQueryExten- 
       sion() XdbeSwapBuffers().