GLwDrawingArea(3X)GLwDrawingArea(3X)NAME
GLwDrawingArea, GLwMDrawingArea -- OpenGL drawing widgets.
SYNOPSIS
#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
DESCRIPTIONGLwDrawingArea 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 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.
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).
GLwNallocateBackground
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.)
GLwNallocateOtherColors
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.
GLwNattribList
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.
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 callback can be used to
perform any appropriate OpenGL initialization such as creating a
context. The callback 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 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.
GLwNinstallBackground
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.
GLwNinstallColormap
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.
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 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;
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 respectively. GLwCR_GINIT does not have a Motif
equivalent.
event Points to the XEvent that triggered the callback. This is NULL
for GLwNginitCallback and GLwNresizeCallback.
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 available.
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 <stdlib.h>
#include <GL/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, NULL);
XtAddCallback(glw, GLwNresizeCallback, resizeCB, NULL);
XtAddCallback(glw, GLwNginitCallback, ginitCB, NULL);
/* 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,
NULL, GL_FALSE);
GLwDrawingAreaMakeCurrent(w, glx_context);
/* Perform any necessary graphics initialization.*/
}
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.
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.
SEE ALSOglXChooseVisual(3G), GLwDrawingAreaMakeCurrent(3X), glXMakeCurrent(3G),
GLwDrawingAreaSwapBuffers(3X)GLwCreateMDraw(3X), Core(3X),
XmPrimitive(3X), VirtualBindings(3X), XSetWMColormapWindows(3X11) and
the OpenGL spec.
March 1, 2011
