Signature
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
.