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
          support 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
          XdbeScreenVisualInfo 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.
          perflevel 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 better
          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
          perflevels, 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(),
          XdbeDeallocateBackBufferName(), XdbeEndIdiom(),
          XdbeFreeVisualInfo(), XdbeGetBackBufferAttributes(),
          XdbeQueryExtension(), XdbeSwapBuffers().