Login or Register to Ask a Question and Join Our Community

Linux and UNIX Man Pages

Linux & Unix Commands - Search Man Pages

glutestablishoverlay(3glut) [suse man page]

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 current 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 win-
       dow  with  the  current initial display mode. Do not attempt to establish an overlay when one is not possible; GLUT will terminate the pro-
       gram.

       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 immediately 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
       normal 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 determine 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, glutRemoveLayer, glutCreateWindow, glutPostOverlayRedisplay, glutShowOverlay, glutOverlayDisplayFunc

AUTHOR

       Mark J. Kilgard (mjk@nvidia.com)

GLUT
									3.7					       glutEstablishOverlay(3GLUT)

Check Out this Related Man Page

glutOverlayDisplayFunc(3GLUT)					       GLUT					     glutOverlayDisplayFunc(3GLUT)

NAME

       glutOverlayDisplayFunc - sets the overlay display callback for the current window.

SYNTAX

       void glutOverlayDisplayFunc(void (*func)(void));

ARGUMENTS

       func	 The new overlay display callback function.

DESCRIPTION

       glutDisplayFunc sets the overlay display callback for the current window. The overlay display callback is functionally the same as the win-
       dow's display callback except that the overlay display callback is used to redisplay the window's overlay.

       When GLUT determines that the overlay plane for the window needs to be redisplayed, the overlay display callback for the window is  called.
       Before  the  callback,  the  current  window is set to the window needing to be redisplayed and the layer in use is set to the overlay. The
       overlay display callback is called with no parameters. The entire overlay region should be redisplayed in response to  the  callback  (this
       includes ancillary buffers if your program depends on their state).

       GLUT  determines when the overlay display callback should be triggered based on the window's overlay redisplay state. The overlay redisplay
       state for a window can be either set explicitly by calling glutPostOverlayRedisplay or implicitly as the result of window  damage  reported
       by the window system. Multiple posted overlay redisplays for a window are coalesced by GLUT to minimize the number of overlay display call-
       backs called.

       Upon return from the overlay display callback, the overlay damaged state of the window (returned by calling  glutLayerGet(GLUT_OVERLAY_DAM-
       AGED) is cleared.

       The  overlay display callback can be deregistered by passing NULL to glutOverlayDisplayFunc. The overlay display callback is initially NULL
       when an overlay is established. See glutDisplayFunc to understand how the display callback alone is used if an overlay display callback	is
       not registered.

SEE ALSO

       glutDisplayFunc, glutPostOverlayRedisplay

AUTHOR

       Mark J. Kilgard (mjk@nvidia.com)

GLUT
									3.7					     glutOverlayDisplayFunc(3GLUT)
Man Page