glutEstablishOverlay(3GLUT) GLUT glutEstablishOverlay(3GLUT)
NAME
glutEstablishOverlay - establishes an overlay (if possible) for the
current window.
SYNTAX
void glutEstablishOverlay(void);
DESCRIPTION
glutEstablishOverlay establishes an overlay (if possible) for the cur-
rent window. The requested display mode for the overlay is determined
by the initial display mode. glutLayerGet(GLUT_OVERLAY_POSSIBLE) can
be called to determine if an overlay is possible for the current window
with the current initial display mode. Do not attempt to establish an
overlay when one is not possible; GLUT will terminate the program.
If glutEstablishOverlay is called when an overlay already exists, the
existing overlay is first removed, and then a new overlay is estab-
lished. The state of the old overlay's OpenGL context is discarded.
The initial display state of an overlay is shown, however the overlay
is only actually shown if the overlay's window is shown.
Implicitly, the window's layer in use changes to the overlay immedi-
ately after the overlay is established.
EXAMPLE
Establishing an overlay is a bit involved, but easy once you get the
hang of it. Here is an example:
int overlaySupport;
int transparent, red, white;
glutInitDisplayMode(GLUT_SINGLE | GLUT_INDEX);
overlaySupport = glutLayerGet(GLUT_OVERLAY_POSSIBLE);
if (overlaySupport) {
glutEstablishOverlay();
glutHideOverlay();
transparent = glutLayerGet(GLUT_TRANSPARENT_INDEX);
glClearIndex(transparent);
red = (transparent + 1) % glutGet(GLUT_WINDOW_COLORMAP_SIZE);
white = (transparent + 2) % glutGet(GLUT_WINDOW_COLORMAP_SIZE);
glutSetColor(red, 1.0, 0.0, 0.0); /* Red. */
glutSetColor(white, 1.0, 1.0, 1.0); /* White. */
glutOverlayDisplayFunc(redrawOverlay);
glutReshapeFunc(reshape);
} else {
printf("Sorry, no nifty overlay (try an SGI workstation)!0);
}
If you setup an overlay and you install a reshape callback, you need to
update the viewports and possibly projection matrices of both the nor-
mal plane and the overlay. For example, your reshape callback might
look like this:
void
reshape(int w, int h)
{
if (overlaySupport) {
glutUseLayer(GLUT_OVERLAY);
/* Setup overlay to have X style coordinate system. */
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, w, 0, h);
glScalef(1, -1, 1);
glTranslatef(0, -h, 0);
glMatrixMode(GL_MODELVIEW);
glutUseLayer(GLUT_NORMAL);
}
glViewport(0, 0, w, h);
}
See the glutOverlayDisplayFunc man page for an example showing one way
to write your overlay display callback.
X IMPLEMENTATION NOTES
GLUT for X uses the SERVER_OVERLAY_VISUALS convention is used to deter-
mine if overlay visuals are available. While the convention allows for
opaque overlays (no transparency) and overlays with the transparency
specified as a bitmask, GLUT overlay management only provides access to
transparent pixel overlays.
Until RGBA overlays are better understood, GLUT only supports color
index overlays.
SEE ALSO
glutUseLayer(3), glutRemoveLayer(3), glutCreateWindow(3),
glutPostOverlayRedisplay(3), glutShowOverlay(3),
glutOverlayDisplayFunc(3)
AUTHOR
Mark J. Kilgard (mjk@nvidia.com)
GLUT 3.7 glutEstablishOverlay(3GLUT)
Mac OS X 10.6 - Generated Thu Sep 17 20:20:39 CDT 2009