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83 lines
3.5 KiB
83 lines
3.5 KiB
13 years ago
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/*! \page opengl-overlay-x11-example.html
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\ingroup opengl-examples
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\title OpenGL Overlay X11 Example
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\warning From version 5.0 onwards, the Qt OpenGL Extension includes
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direct support for use of OpenGL overlays. For many uses of overlays,
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this makes the technique described below redundant. See the \link
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opengl-overlay-example.html overlay\endlink example program. The
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following is a discussion on how to use non-QGL widgets in overlay
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planes.
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Overlayrubber: An example program showing how to use Qt and Qt OpenGL
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Extension with X11 overlay visuals.
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See \c{$QTDIR/examples/opengl/overlay_x11} for the source code.
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Background information for this example can be found in the
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information on \link opengl-x11-overlays.html overlays\endlink.
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The example program has three main parts:
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\list 1
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\i \e GearWidget - a normal, simple QGLWidget. This renders the usual
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gears. It has been modified to print a debug message every time it
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redraws (renders) itself. Thus, you can easily confirm that drawing in
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the overlay plane does not cause redrawings in the main plane where
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the QGLWidget resides.
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\i \e RubberbandWidget - Very simple standard (non-GL) Qt widget that
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implements rubberband drawing. Designed for use in an overlay plane.
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It takes the plane's transparent color as a constructor argument and
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uses that for its background color. Thus, the widget itself will be
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invisible, only the rubberbands it draws will be visible.
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\i \e{main.cpp} Creates a GearWidget and a Rubberbandwidget and puts the
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latter on top of the former. Contains a routine that checks that the
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default visual is in an overlay plane, and returns the transparent
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color of that plane.
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\endlist
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\section1 Running the Example
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Start the \c overlayrubber executable. Click and drag with the left
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mouse button to see rubberband drawing. Observe that the QGLWidget
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does not redraw itself (no redraw debug messages are output), and yet
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the image is not destroyed. Marvel at the coolness of X11 overlays!
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\section1 Using this technique in a real application
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For clarity, this example program has been kept very simple. Here are
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some hints for real application usage:
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\list
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\i \e{All normal widgets are in the overlay plane.} This means that you
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can put all kinds of Qt widgets (your own or standard Qt widgets) on
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top of the OpenGL image (widget), e.g. pushbuttons etc., and they can
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be moved, resized, or removed without destroying the OpenGL image.
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\i \e{Using with geometry management.} The QLayout classes don't permit
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putting one widget (the overlay) on top of another (the OpenGL
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widget); that would defy the whole purpose of the automatic layout.
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The solution is to add just one of them to the QLayout object. Have it
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keep a pointer to the other (i.e. the QGLWidget knows about its
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overlay widget or vice versa). Implement the resizeEvent() method of
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the widget you put in the layout, and make it call setGeometry() on
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the other widget with its own geometry as parameters, thus keeping the
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two widgets' geometries synchronized.
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\i \e{Using together with QPalette and QColorGroup.} Instead of the
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simplistic setBackgroundColor( transparentColor ), you can
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use Qt's QPalette system to make your overlay widgets use
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transparent color for what you want. This way, the normal Qt widgets
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can be used as overlays for fancy effects. Just create a palette for
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them with the transparent color for the relevant color roles, e.g.
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Background and Base, in the Normal and/or Active modes. This way, you
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can create see-through QPushButtons etc.
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\endlist
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*/
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