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glutPostOverlayRedisplay(3GLUT)      GLUT      glutPostOverlayRedisplay(3GLUT)


NAME

       glutPostOverlayRedisplay, glutPostWindowOverlayRedisplay - marks the
       overlay of the current or specified window as needing to be
       redisplayed.


SYNTAX


       void glutPostOverlayRedisplay(void);
       void glutPostWindowOverlayRedisplay(int win);


DESCRIPTION

       Mark the overlay of current window as needing to be redisplayed.  The
       next iteration through glutMainLoop, the window's overlay display
       callback (or simply the display callback if no overlay display callback
       is registered) will be called to redisplay the window's overlay plane.
       Multiple calls to glutPostOverlayRedisplay before the next display
       callback opportunity (or overlay display callback opportunity if one is
       registered) generate only a single redisplay. glutPostOverlayRedisplay
       may be called within a window's display or overlay display callback to
       re-mark that window for redisplay.

       Logically, overlay damage notification for a window is treated as a
       glutPostOverlayRedisplay on the damaged window. Unlike damage reported
       by the window system, glutPostOverlayRedisplay will not set to true the
       overlay's damaged status (returned by
       glutLayerGet(GLUT_OVERLAY_DAMAGED).

       If the window you want to post an overlay redisplay on is not already
       current (and you do not require it to be immediately made current),
       using glutPostWindowOverlayRedisplay is more efficient that calling
       glutSetWindow to the desired window and then calling
       glutPostOverlayRedisplay.


EXAMPLE

       If you are doing an interactive effect like rubberbanding in the
       overlay, it is a good idea to structure your rendering to minimize
       flicker (most overlays are single-buffered).  Only clear the overlay if
       you know that the window has been damaged.  Otherwise, try to simply
       erase what you last drew and redraw it in an updated position.  Here is
       an example overlay display callback used to implement overlay
       rubberbanding:

         void
         redrawOverlay(void)
         {
           static int prevStretchX, prevStretchY;

           if (glutLayerGet(GLUT_OVERLAY_DAMAGED)) {
             /* Damage means we need a full clear. */
             glClear(GL_COLOR_BUFFER_BIT);
           } else {
             /* Undraw last rubber-band. */
             glIndexi(transparent);
             glBegin(GL_LINE_LOOP);
             glVertex2i(anchorX, anchorY);
             glVertex2i(anchorX, prevStretchY);
             glVertex2i(prevStretchX, prevStretchY);
             glVertex2i(prevStretchX, anchorY);
             glEnd();
           }
           glIndexi(red);
           glBegin(GL_LINE_LOOP);
           glVertex2i(anchorX, anchorY);
           glVertex2i(anchorX, stretchY);
           glVertex2i(stretchX, stretchY);
           glVertex2i(stretchX, anchorY);
           glEnd();
           prevStretchX = stretchX;
           prevStretchY = stretchY;
         }

       Notice how glutLayerGet(GLUT_OVERLAY_DAMAGED) is used to determine if a
       clear needs to take place because of damage; if a clear is unnecessary,
       it is faster to just draw the last rubberband using the transparent
       pixel.

       When the application is through with the rubberbanding effect, the best
       way to get ride of the rubberband is to simply hide the overlay by
       calling glutHideOverlay.


SEE ALSO

       glutPostRedisplay, glutEstablishOverlay, glutLayerGet


AUTHOR

       Mark J. Kilgard (mjk@nvidia.com)

GLUT                                  3.7      glutPostOverlayRedisplay(3GLUT)

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