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NAME
GLwDrawingArea, GLwMDrawingArea - Open GL drawing widgets.
SYNOPSIS
#include <X11/GLw/GLwDrawA.h>
widget = XtCreateWidget(widget, glwDrawingAreaWidgetClass,
...);
ld ... -lGLw -l<anywidgetlibrary> -lXt -lGL -lX11 ...
#include <X11/GLw/GLwMDrawA.h>
widget = XtCreateWidget(widget, glwMDrawingAreaWidgetClass,
...);
ld ... -lGLw -lXm -lXt -lGL -lX11 ...
DESCRIPTION
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 Motif widget class XmPrimitive and
has resources and defaults suitable for use with Motif. For
example, GLwMDrawingArea provides the default Motif back-
ground 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 else-
where; 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 identi-
cally to that used for direct OpenGL 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 are created in 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 appli-
cation 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 OpenGL 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 win-
dow.
GLwDrawingArea Classes
GLwDrawingArea inherits behavior and resources from the Core
class.
The class pointer is GLwDrawingAreaClass.
The class name is GLwDrawingArea.
GLwMDrawingArea Classes
GLwMDrawingArea inherits behavior and resources from the
XmPrimitive and Core classes.
The class pointer is GLwMDrawingAreaClass.
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 glXChooseV-
isual. As with glXChooseVisual, all Boolean resources
default to FALSE and all integer resources default to 0.
These resources can all be set only at creation time, and
are used to determine the visual. If either the GLwNattri-
bList or GLwNvisualInfo resource is set, these resources are
ignored. The specific meaning of these resources is dis-
cussed in the glXChooseVisual manual page and will not be
discussed here.
__________________________________________________________________________
| Name | Class | Type | OpenGL attribute |
|__________________|____________________|_________|______________________|
|GLwNbufferSize | GLwCBufferSize | int | GLX_BUFFER_SIZE |
|__________________|____________________|_________|______________________|
|GLwNlevel | GLwCLevel | int | GLX_LEVEL |
|__________________|____________________|_________|______________________|
|GLwNrgba | GLwCRgba | Boolean| GLX_RGBA |
|__________________|____________________|_________|______________________|
|GLwNdoublebuffer | GLwCDoublebuffer | Boolean| GLX_DOUBLEBUFFER |
|__________________|____________________|_________|______________________|
|GLwNstereo | GLwCStereo | Boolean| GLX_STEREO |
|__________________|____________________|_________|______________________|
|GLwNauxBuffers | GLwCAuxBuffers | Boolean| GLX_AUX_BUFFERS |
|__________________|____________________|_________|______________________|
|GLwNredSize | GLwCColorSize | int | GLX_RED_SIZE |
|__________________|____________________|_________|______________________|
|GLwNgreenSize | GLwCColorSize | int | GLX_GREEN_SIZE |
|__________________|____________________|_________|______________________|
|GLwNblueSize | GLwCColorSize | int | GLX_BLUE_SIZE |
|__________________|____________________|_________|______________________|
|GLwNalphaSize | GLwCAlphaSize | int | GLX_ALPHA_SIZE |
|__________________|____________________|_________|______________________|
|GLwNDepthSize | GLwCDepthSize | int | GLX_DEPTH_SIZE |
|__________________|____________________|_________|______________________|
|GLwNStencilSize | GLwCStencilSize | int | GLX_STENCIL_SIZE |
|__________________|____________________|_________|______________________|
|GLwNaccumRedSize | GLwCAccumColorSize| int | GLX_ACCUM_RED_SIZE |
|__________________|____________________|_________|______________________|
|GLwNaccumGreenSize| GLwCAccumColorSize| int | GLX_ACCUM_GREEN_SIZE|
|__________________|____________________|_________|______________________|
|GLwNaccumBlueSize | GLwCAccumColorSize| int | GLX_ACCUM_BLUE_SIZE |
|__________________|____________________|_________|______________________|
|GLwNaccumAlphaSize| GLwCAccumAlphaSize| int | GLX_ACCUM_ALPHA_SIZE|
|__________________|____________________|_________|______________________|
The following table lists other resources of the
GLwDrawingArea widget. each of these will be described sub-
sequently 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).
____________________________________________________________________________
| Name | Class | Type | Default|
|_______________________|_______________________|________________|_________|
|_______________________|_______________________|________________|_________|
|GLwNallocateBackground | GLwCAllocateColors | Boolean | FALSE |
|_______________________|_______________________|________________|_________|
|GLwNallocateOtherColors| GLwCAllocateColors | Boolean | FALSE |
|_______________________|_______________________|________________|_________|
|GLwNattribList | GLwCAttribList | int * | NULL |
|_______________________|_______________________|________________|_________|
|GLwNexposeCallback | GLwCCallback | XtCallbackList| NULL |
|_______________________|_______________________|________________|_________|
|GLwNginitCallback | GLwCCallback | XtCallbackList| NULL |
|_______________________|_______________________|________________|_________|
|GLwNinputCallback | GLwCCallback | XtCallbackList| NULL |
|_______________________|_______________________|________________|_________|
|GLwNinstallBackground | GLwCInstallBackground| Boolean | TRUE |
|_______________________|_______________________|________________|_________|
|GLwNinstallColormap | GLwCInstallColormap | Boolean | TRUE |
|_______________________|_______________________|________________|_________|
|GLwNresizeCallback | GLwCCallback | XtCallbackList| NULL |
|_______________________|_______________________|________________|_________|
|GLwNvisualInfo | GLwCVisualInfo | XVisualInfo* | NULL |
|_______________________|_______________________|________________|_________|
GLwNallocateBackground
If TRUE, the background pixel and pixmap will be allo-
cated if appropriate using the newly calculated color-
map and visual. If FALSE, they will retain values cal-
culated using the parent's colormap and visual. Appli-
cations 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 allo-
cated colormap. Also, on hardware that supports only
one colormap, the application may need to do more care-
ful 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 color-
map.)
GLwNallocateOtherColors
This is similar to GLwNallocateBackground, but allo-
cates 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 calcu-
lated.
GLwNattribList
Contains the list of attributes suitable for a call to
glXChooseVisual. If this resource is NULL, it is cal-
culated based on the attribute resources. If it is not
NULL, the attribute resources are ignored.
GLwNexposeCallback
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.
GLwNginitCallback
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 call-
back can be used to perform any appropriate open GL
initialization such as creating a context. The call-
back reason is GLwCR_GINIT.
GLwNinputCallback
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 con-
venience, 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 transla-
tions can also provide for more customizability.
GLwNinstallBackground
If set to TRUE, the background is installed on the win-
dow. If set to FALSE, the window has no background.
This resource has no effect unless GLwNallocateBack-
ground is also TRUE.
GLwNinstallColormap
If set to TRUE, the widget will call XSetWMColormapWin-
dows 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 multi-
ple GLwDrawingAreas sharing a single colormap, it is
most efficient to set this resource to TRUE for exactly
one GLwDrawingArea with each colormap. If an applica-
tion needs additional control over the order of color-
maps, this resource can be set to FALSE, with the
application calling XSetWMColormapWindows explicitly.
GLwNresizeCallback
Specifies the list of callbacks that is called when the
GLwDrawingArea is resized. The callback reason is
GLwCR_RESIZE.
GLwNvisualInfo
Contains a pointer to the window's visual info struc-
ture. 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 GLwNat-
tributList 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 dis-
abled 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 call-
back:
typedef struct
{
int reason;
XEvent * event;
Dimensionwidth, height;
} GLwDrawingAreaCallbackStruct;
reason 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 respec-
tively. GLwCR_GINIT does not have a Motif
equivalent.
event Points to the XEvent that triggered the callback.
This is NULL for GLwNginitCallback and GLwNresize-
Callback.
width and height
Are set to the width and height of the window.
Translations
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:
glwInput():
Called whenever one of the above translations specifies
that input has occurred. Its sole purpose is to call
the input callback.
INITIALIZATION
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 avail-
able.
Between the time the widget is created and it is realized,
the following apply:
o No OpenGL operations can be done to the window
o No resize callbacks are generated.
o The normal window is available (XtWindow returns NULL).
o GLwDrawingAreaMakeCurrent (and glXMakeCurrent) should
not be called.
When the widget is realized, the following actions take
place:
o The window is created.
o The ginit callback is called. The user may use this
callback to perform any needed OpenGL initialization to
the window.
NOTES
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.
EXAMPLE
Here are some code fragments that create a GLwDrawingArea
widget, and manage the appropriate callbacks.
#include <X11/GLw/GLwDrawA.h>
static GLXContext glx_context; /* assume only one context */
. . .
main()
{
Arg args[10];
int n;
Widget parent;/* The parent of the gl widget */
Widget glw;/* The GLwDrawingArea widget */
. . .
/* Create the widget using RGB mode. This can also be set
* in an X Defaults file
*/
n = 0;
XtSetArg(args[n], GLwNrgba, TRUE); n++;
glw = XtCreateManagedWidget("glw", GLwDrawingAreaWidgetClass,
parent, args, n);
XtAddCallback(glw, GLwNexposeCallback, exposeCB, 0);
XtAddCallback(glw, GLwNresizeCallback, resizeCB, 0);
XtAddCallback(glw, GLwNginitCallback, ginitCB, 0);
/* Also add input callback if needed */
. . .
}
static void
exposeCB(Widget w, XtPointer client_data,
GLwDrawingAreaCallbackStruct call_data)
{
GLwDrawingAreaMakeCurrent (w, glx_context);
/* redraw the display */
}
static void
resizeCB(Widget w, XtPointer client_data,
GLwDrawingAreaCallbackStruct call_data)
{
GLwDrawingAreaMakeCurrent (w, glx_context);
/* perform any resize actions */
}
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);
/* create a visual context */
glx_context = glXCreateContext(XtDisplay(w), vi, 0, GL_FALSE);
GLwDrawingAreaMakeCurrent (w, glx_context);
/* Perform any necessary graphics initialization.*/
}
The Motif program need only differ by including GLwMDrawA.h
instead of GLwDrawA.h and by creating a widget of type
GLwMDrawingAreaWidgetClass instead of
GLwDrawingAreaWidgetClass. As an alternative, the Motif
program could use GLwCreateMDraw(3X) instead.
WARNINGS
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.
RELATED INFORMATION
glXChooseVisual, GLwDrawingAreaMakeCurrent, glXMakeCurrent,
GLwDrawingAreaSwapBuffers GLwCreateMDraw, Core(3X),
XmPrimitive(3X), VirtualBindings(3X), glFlush(3gl),
XSetWMColormapWindows(3X11) and the OpenGL spec.
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