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glutestablishoverlay(3glut) [osx man page]

glutEstablishOverlay(3GLUT)					       GLUT					       glutEstablishOverlay(3GLUT)

glutEstablishOverlay - establishes an overlay (if possible) for the current window. SYNTAX
#include <GLUT/glut.h> 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 ( GLUT
3.7 glutEstablishOverlay(3GLUT)

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glutOverlayDisplayFunc(3GLUT)					       GLUT					     glutOverlayDisplayFunc(3GLUT)

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 ( GLUT
3.7 glutOverlayDisplayFunc(3GLUT)
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