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GLwDrawingArea, GLwMDrawingArea -- OpenGL drawing widgets.


#include <GL/GLwDrawA.h>
ld ... -lGLw -lGL -l<anywidgetlibrary> -lXext -lXt -lX11 -lm

#include <GL/GLwMDrawA.h>
ld ... -lGLw -lGL -lXm -lXext -lXt -lX11 -lm


GLwDrawingArea and GLwMDrawingArea are widgets suitable for OpenGL drawing. They provide a window with the appropriate visual and colormaps needed for OpenGL, based on supplied parameters. GLwDrawingArea and GLwMDrawingArea also provide callbacks for redraw, resize, input, and initialization.

GLwDrawingArea is not a part of any widget set, but depends only on Xt. GLwDrawingArea can be used with any widget set. GLwMDrawingArea is identical to GLwDrawingArea except that it is a subclass of the MotifTm widget class XmPrimitive and has resources and defaults suitable for use with Motif. For example, GLwMDrawingArea provides the default Motif background and foreground colors for resources, and deals better with keyboard traversal. Although the GLwDrawingArea widget can be used in a Motif program, it is recommended that GLwMDrawingArea be used instead.

Since both GLwDrawingArea and GLwMDrawingArea widgets behave almost identically, the remainder of this manual page will refer only to GLwDrawingArea, except when the behaviors differ. Unless explicitly stated, all statements about GLwDrawingArea also apply to GLwMDrawingArea.

Among the information provided when creating a GLwDrawingArea is information necessary to determine the visual. This may be provided in three ways, all of them through resources. A specific visualInfo structure may be passed in. (This visualInfo must have been obtained elsewhere; it is the application designer's responsibility to make sure that it is compatible with the OpenGL rendering done by the application). Alternatively, an attribute list may be provided. This attribute list is formatted identically to that used for direct open GL programming. Finally, each attribute can be specified as an individual resource. The latter method is the simplest, and is the only method that works from resource files.

In addition to allocating the visual, the GLwDrawingArea will also allocate the colormap unless one is provided by the application. (If one is provided it is the application writer's responsibility to guarantee compatibility between the colormap and the visual). If an application creates multiple GLwDrawingAreas with the same visual, the same colormap will be used. (However the colormap will not be shared among separate applications).

Creating the widget does not actually create the window until it is realized, and consequently, the application should not perform any OpenGL operations to the window immediately after creation. Instead the application must wait until after it has realized the window. Alternatively, the ginit callback may be used to indicate when the window has been created. Upon receiving this callback, the application can perform all OpenGL initialization for the window, and can subsequently perform other operations on it. The initialization is discussed in more detail below.

Applications select which GLwDrawingArea they are accessing using either glXMakeCurrent or the convenience function GLwDrawingAreaMakeCurrent which uses a widget instead of a display and window. If there is only one GLwDrawingArea this need only be called once, however if there is more than one GLwDrawingArea it should be called at the start of each callback. Callbacks in this case include not only callbacks provided by the widget itself, but any other callback that leads to GL activity such as a timeout or a workproc.

If an application is using double buffering, it may call GLwDrawingAreaSwapBuffers instead of glXSwapBuffers. This allows the use of the widget instead of the display and window.

GLwDrawingArea Classes

GLwDrawingArea inherits behavior and resources from the Core class.
The class pointer is glwDrawingAreaWidgetClass.
The class name is GLwDrawingArea.

GLwMDrawingArea Classes

GLwMDrawingArea inherits behavior and resources from the XmPrimitive and Core classes.
The class pointer is glwMDrawingAreaWidgetClass.
The class name is GLwMDrawingArea.

New Resources

The following tables define a set of widget resources used by the programmer to specify data. The programmer can also set the resource values for the inherited classes to set attributes for this widget. To reference a resource by name or by class in a .Xdefaults file, remove the GLwN or GLwC prefix and use the remaining letters. There are two tables included. The first table includes resources that correspond directly to the attributes used by glXChooseVisual. As with glXChooseVisual, all Boolean resources default to FALSE and all integer resources default to 0, except redSize, greenSize and blueSize which default to 1. These resources can all be set only at creation time, and are used to determine the visual. If either the GLwNattribList or GLwNvisualInfo resource is set, these resources are ignored. The specific meaning of these resources is discussed in the glXChooseVisual manual page and will not be discussed here.

NameClassTypeOpenGL attribute

The following table lists other resources of the GLwDrawingArea widget. each of these will be described subsequently. The codes in the access column indicate if the given resource can be set at creation time (C), set by using XtSetValues (S), retrieved by using XtGetValues (G), or is not applicable (N/A).

GLwNattribListGLwCAttribListint *NULLCG

If TRUE, the background pixel and pixmap will be allocated if appropriate using the newly calculated colormap and visual. If FALSE, they will retain values calculated using the parent's colormap and visual. Applications which wish to have X clear their background for them will usually set this to TRUE. Applications clearing their own background will often set this to FALSE, although they may set this to TRUE if they query the background for their own use. One reason to leave this resource FALSE is that if color index mode is in use this avoid using up a pixel from the newly allocated colormap. Also, on hardware that supports only one colormap, the application may need to do more careful color allocation to avoid flashing between the OpenGL colormap and the default X colormap. (Note that because of the way Xt works, the background colors are originally calculated using the default colormap; if this resource is set they can be recalculated correctly. If a colormap was explicitly supplied to the widget rather than being dynamically calculated, these resources are always calculated using that colormap.)

This is similar to GLwNallocateBackground, but allocates other colors normally allocated by widgets. Although the GLwDrawingArea and GLwMDrawingArea widget do not make use of these colors the application may choose to query them. For the non-Motif GLwDrawingArea widget there are no other colors allocated, so this resource is a no-op. For the Motif GLwMDrawingArea are widget, the XmPrimitive resources XmNforeground, XmNhighlightColor, and XmNhighlightPixmap are calculated.

Contains the list of attributes suitable for a call to glXChooseVisual. If this resource is NULL, it is calculated based on the attribute resources. If it is not NULL, the attribute resources are ignored.

Specifies the list of callbacks that is called when the widget receives an exposure event. The callback reason is GLwCR_EXPOSE. The callback structure also includes the exposure event. The application will generally want to redraw the scene.

Specifies the list of callbacks that is called when the widget is first realized. Since no OpenGL operations can be done before the widget is realized, this callback can be used to perform any appropriate OpenGL initialization such as creating a context. The callback reason is GLwCR_GINIT.

Specifies the list of callbacks that is called when the widget receives a keyboard or mouse event. By default, the input callback is called on each key press and key release, on each mouse button press and release, and whenever the mouse is moved while a button is pressed. However this can be changed by providing a different translation table. The callback structure also includes the input event. The callback reason is GLwCR_INPUT.

The input callback is provided as a programming convenience, as it provides a convenient way to catch all input events. However, a more modular program can often be obtained by providing specific actions and translations in the application rather than using a single catch all callback. Use of explicit translations can also provide for more customization.

If set to TRUE, the background is installed on the window. If set to FALSE, the window has no background. This resource has no effect unless GLwNallocateBackground is also TRUE.

If set to TRUE, the widget will call XSetWMColormapWindows to tell the window manager to install the colormap when the window's shell has focus. If set to FALSE, this will not be called. For applications with multiple GLwDrawingAreas sharing a single colormap, it is most efficient to set this resource to TRUE for exactly one GLwDrawingArea with each colormap. If an application needs additional control over the order of colormaps, this resource can be set to FALSE, with the application calling XSetWMColormapWindows explicitly.

Specifies the list of callbacks that is called when the GLwDrawingArea is resized. The callback reason is GLwCR_RESIZE.

Contains a pointer to the window's visual info structure. If NULL, the visualInfo is calculated at widget creation time based on the GLwNattributeList resource (which is itself calculated from the various resources). If GLwNvisualInfo is not NULL the GLwNattributList and the attribute resources are ignored.

Inherited Resources

Both GLwDrawingArea and GLwMDrawingArea inherit behavior and resources from the core superclass. Other than the behavior of the colormap and background resources described previously, all defaults are the same as for core.

In addition, the Motif version GLwMDrawingArea also inherits from XmPrimitive. The behavior of the color resources has been described previously. The TraversalOn resource is disabled for this widget, but if keyboard input is required it should be enabled. (Also, the application should call XmProcessTraversal(widget, XmTRAVERSE_CURRENT) whenever mouse button 1 is clicked in the widget. This is similar to the requirements of the Motif Drawing area.) Because Motif gets confused by having multiple visuals in one top level shell, XmNhighlightOnEnter has been disabled, and XmNhighlightThickness has been set to 0.

Callback Information

A pointer to the following structure is passed to each callback:

typedef struct
    int     reason;
    XEvent    *event;
    Dimension     width, height;
} GLwDrawingAreaCallbackStruct;

Indicates why the callback was invoked. Appropriate values are stated in the above resource descriptions. For Motif programmers, the values GLwCR_EXPOSE, GLwCR_RESIZE, and GLwCR_INPUT are equal to XmCR_EXPOSE, XmCR_RESIZE, and XmCR_INPUT respectively. GLwCR_GINIT does not have a Motif equivalent.

Points to the XEvent that triggered the callback. This is NULL for GLwNginitCallback and GLwNresizeCallback.

Are set to the width and height of the window.


GLwDrawingArea has the translations listed below.
<KeyDown>:    glwInput()
<KeyUp>:    glwInput()
<BtnDown>:    glwInput()
<BtnUp>:    glwInput()
<BtnMotion>:    glwInput()

GLwMDrawingArea has the following additional translation:

<Key>osfHelp:    PrimitiveHelp()

An application wishing to catch other events than these defaults can do so by installing a different translation table.

Action Routines

The GLwDrawingArea has the following action routine:

Called whenever one of the above translations specifies that input has occurred. Its sole purpose is to call the input callback.


When the widget is initially created (e.g. through XtCreateWidget(3X) ) the associated window is not actually created. Instead, window creation is delayed until the widget is realized. However, glXchooseVisual is called immediately, so information based on its results is available.

Between the time the widget is created and it is realized, the following apply:

When the widget is realized, the following actions take place:


When using the input callback to receive keyboard input, the keycode in the event must be converted to a KeySym. Use XLookupKeysym(3X) or XLookupString(3X) to do the conversion. Keyboard input can also be dealt using translations, in which case no such conversion is required.

Motif programmers should keep in mind that OSF uses virtual bindings and replaces some of the key bindings. As a common example, if the ESC key is to be used to exit the program (as it often is in GL programs), the translation should specify <key>osfCancel instead of <key>Escape.

Motif programmers may also create a GLwMDrawingArea widget with the Motif style GLwCreateMDrawingArea.


Here are some code fragments that create a GLwDrawingArea widget, and manage the appropriate callbacks.

   #include <stdlib.h>
   #include <GL/GLwDrawA.h>
   static GLXContext glx_context;  
   . . .
       Arg args[10];
       int n;
       Widget parent;    
       Widget glw;       
       . . .
       n = 0;
       XtSetArg(args[n], GLwNrgba, True); n++;
       glw = XtCreateManagedWidget("glw", glwDrawingAreaWidgetClass,
                                   parent, args, n);
       XtAddCallback(glw, GLwNexposeCallback, exposeCB, NULL);
       XtAddCallback(glw, GLwNresizeCallback, resizeCB, NULL);
       XtAddCallback(glw, GLwNginitCallback, ginitCB, NULL);
       . . .
   static void
   exposeCB(Widget w, XtPointer client_data,
            GLwDrawingAreaCallbackStruct *call_data)
       GLwDrawingAreaMakeCurrent(w, glx_context);
   static void
   resizeCB(Widget w, XtPointer client_data,
            GLwDrawingAreaCallbackStruct *call_data)
       GLwDrawingAreaMakeCurrent(w, glx_context);
   static void
   ginitCB(Widget w, XtPointer client_data,
           GLwDrawingAreaCallbackStruct *call_data)
       Arg args[1];
       XVisualInfo *vi;
       XtSetArg(args[0], GLwNvisualInfo, &vi);
       XtGetValues(w, args, 1);
       glx_context = glXCreateContext(XtDisplay(w), vi,
                                      NULL, GL_FALSE);
       GLwDrawingAreaMakeCurrent(w, glx_context);

The Motif program need only differ by including GLwMDrawingArea.h instead of GLwDrawingArea.h and by creating a widget of type GLwMDrawingAreaWidgetClass instead of GLwDrawingAreaWidgetClass. As an alternative, the Motif program could use GLwCreateMDraw(3X) instead.


If a GLwDrawingArea widget is created as a child of an already realized widget, the GLwDrawingArea widget will be created immediately, without giving the user an opportunity to add the ginit callback. In such a case, initialization should be done immediately after creating the widget rather than by using the callback.

If the non-Motif GLwDrawingArea widget is used in a Motif program and keyboard traversal is attempted, the behavior is undefined if the user traverses into the GLwDrawingArea widget.

See Also

glXChooseVisual(3G) , GLwDrawingAreaMakeCurrent(3X) , glXMakeCurrent(3G) , GLwDrawingAreaSwapBuffers(3X) GLwCreateMDraw(3X) , Core(3X) , XmPrimitive(3X) , VirtualBindings(3X) , XSetWMColormapWindows(3X11) and the OpenGL spec.

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