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Overlays
[OpenGLUT API Reference]


Functions

void glutEstablishOverlay (void)
void glutHideOverlay (void)
int glutLayerGet (GLenum eWhat)
void glutPostOverlayRedisplay (void)
void glutPostWindowOverlayRedisplay (int ID)
void glutRemoveOverlay (void)
void glutShowOverlay (void)
void glutUseLayer (GLenum layer)

Detailed Description

Some windows may be able to handle one or more overlays. That is, some windows may be able to have a secondary bitmap that is placed over the normal display. This allows two or more bitmapped images to be displayed in a single window without directly intefering with one other---beyond the fact that one may obscure the other. The value here is that then the overlain bitmap may be removed or hidden and the underlain graphics will appear without requiring a redraw.

Old GLUT only supported indexed color for overlays. freeglut ignores all overlay requests. OpenGLUT has inherited freeglut's treatment. OpenGLUT has neither resolved to fully support overlays, nor to remove them.

Function Documentation

void glutEstablishOverlay (  void   ) 
 

Creates an overlay.

Creates an overlay associated with the current window.

Note:
Unimplemented.

Old GLUT would terminate the program when an overlay was not possible. freeglut ignores the request; OpenGLUT ignores the request as well.

See also:
glutRemoveOverlay(), glutUseLayer(), glutPostOverlayRedisplay(), glutPostWindowOverlayRedisplay(), glutShowOverlay(), glutHideOverlay()

void glutHideOverlay (  void   ) 
 

Make an overlay invisible.

Causes a visible overlay to become invisible. Applies to the current window.

Note:
Unimplemented.
See also:
glutEstablishOverlay(), glutRemoveOverlay(), glutUseLayer(), glutPostOverlayRedisplay(), glutPostWindowOverlayRedisplay(), glutShowOverlay()

int glutLayerGet (  GLenum  eWhat  ) 
 

Query overlay state/option variables.

Parameters:
eWhat Enumerated parameter ID.
Returns some useful information about layers. Or, it would be useful if layers were implemented... eWhat may be given any of the following values:

  • GLUT_HAS_OVERLAY

  • GLUT_LAYER_IN_USE

  • GLUT_NORMAL_DAMAGED
    0 unless the window system has told us that the normal layer is damaged (glutPostRedisplay() does not affect this).

  • GLUT_OVERLAY_DAMAGED
    Returns -1 if no layer in use.

  • GLUT_OVERLAY_POSSIBLE

  • GLUT_TRANSPARENT_INDEX
    Returns -1 if no layer in use.

All information relates to the current window and any overlay that it may have.

Note:
OpenGLUT does not support overlays.
See also:
glutSetOption(), glutGet(), glutDeviceGet(), glutGetModifiers()

void glutPostOverlayRedisplay (  void   ) 
 

Posts a redispaly against the layer for the current window.

For the current window, tells OpenGLUT that you wish to have your OverlayDisplay callback invoked.

Note:
Unimplemented.
See also:
glutEstablishOverlay(), glutRemoveOverlay(), glutUseLayer(), glutPostWindowOverlayRedisplay(), glutShowOverlay(), glutHideOverlay(), glutOverlayDisplayFunc(), glutPostRedisplay()

void glutPostWindowOverlayRedisplay (  int  ID  ) 
 

Posts a redisplay to the indicated window's layer.

Parameters:
ID A window ID.
This function lets you post an overlay update to the overlay of any arbitrary window.

Note:
Unimplemented.
See also:
glutEstablishOverlay(), glutRemoveOverlay(), glutUseLayer(), glutPostOverlayRedisplay(), glutShowOverlay(), glutHideOverlay(), glutOverlayDisplayFunc(), glutPostRedisplay()

void glutRemoveOverlay (  void   ) 
 

Removes an overlay.

Removes the overlay associated with the current window.

Note:
Unimplemented.
See also:
glutEstablishOverlay(), glutUseLayer(), glutPostOverlayRedisplay(), glutPostWindowOverlayRedisplay(), glutShowOverlay(), glutHideOverlay()

void glutShowOverlay (  void   ) 
 

Make an overlay visible.

Causes a previously-hidden overlay to become apparent. Applies to the current window.

Note:
Unimplemented.
See also:
glutEstablishOverlay(), glutRemoveOverlay(), glutUseLayer(), glutPostOverlayRedisplay(), glutPostWindowOverlayRedisplay(), glutHideOverlay()

void glutUseLayer (  GLenum  layer  ) 
 

Allows you to switch between normal and layer mode.

Parameters:
layer Whether to be in a layer or in the normal window.
By default, OpenGLUT operates in "normal" mode, with respect to layers. If you have a layer open and wish to operate on the layer, you must use glutUseLayer().

layer can take on the following values, indicating the layer mode to use:

  • GLUT_NORMAL
  • GLUT_LAYER

Note:
Unimplemented.

It is unclear what the consequences are if you are in GLUT_OVERLAY mode and switch to another (or the same) window via glutSetWindow(). What if the target has a layer? What if it doesn't?

See also:
glutEstablishOverlay(), glutRemoveOverlay(), glutPostOverlayRedisplay(), glutPostWindowOverlayRedisplay(), glutShowOverlay(), glutHideOverlay()




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