glutPostOverlayRedisplay(3GLUT)GLUglutPostOverlayRedisplay(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 redis
played. The next iteration through glutMainLoop, the win
dow'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 win
dow. Unlike damage reported by the window system, glutPos
tOverlayRedisplay will not set to true the overlay's dam
aged status (returned by glutLayerGet(GLUT_OVERLAY_DAM
AGED).
If the window you want to post an overlay redisplay on is
not already current (and you do not require it to be imme
diately made current), using glutPostWindowOverlayRedis
play 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 ren
dering 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 imple
ment 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 {
GLUT 3.7 1
glutPostOverlayRedisplay(3GLUT)GLUglutPostOverlayRedisplay(3GLUT)
/* 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 dam
age; 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 2
