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75 lines
3.3 KiB
75 lines
3.3 KiB
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UPDATE: From version 5.0 onwards, the TQt 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 'overlay'
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example program. The following is a discussion on how to use non-TQGL
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widgets in overlay planes.
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-----------------------------------------------------------------------
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Overlayrubber: An example program showing how to use TQt and TQt OpenGL
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Extension with X11 overlay visuals.
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(Background information for this example can be found in the file
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README.X11-OVERLAYS)
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The example program has three main parts:
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GearWidget: A simple TQGLWidget that renders the usual gears. Modified
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so that it will print a debug message every time it redraws (renders)
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itself. Thus, you can eaily confirm that drawing in the overlay plane
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does not cause redrawings in the main plane where the TQGLWidget
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resides.
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RubberbandWidget: Very simple standard (non-GL) TQt widget that
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implements rubberband drawing. Designed for use in an overlay
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plane. It takes the planes' transparent color as a constructor
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argument and uses that for its background color. Thus, the widget
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itself will be invisible, only the rubberbands it draws will be
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visible.
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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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Running it:
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-----------
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Start the overlayrubber executable. Click and drag with the left mouse
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button to see rubberband drawing. Observe that the TQGLWidget does
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not redraw itself (no redraw debug messages are output), and yet the
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image is not destroyed. Marvel at the coolness of X11 overlays!
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Using this technique in a real application
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------------------------------------------
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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 use:
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All normal widgets can go in the overlay plane: This means that you
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can put all kinds of TQt widgets (your own or those provided with Qt)
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on top of the OpenGL image (widget), e.g. pushbuttons etc., and they
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can be moved, resized, or removed without destroying the OpenGL image.
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Using with geometry management: The TQLayout classes will not allow you
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to put one widget (the overlay) on top of another (the OpenGL widget);
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that would defy the whole purpose of the automatic layout. The
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solution is to add just one of them to the TQLayout object. Have it
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keep a pointer to the other (i.e. the TQGLWidget 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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Using with TQPalette and TQColorGroup: Instead of the somewhat
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simplistic setBackgroundColor( transparentColor ), you can use Qt's
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TQPalette system for having your overlay widgets use transparent color
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for what you want. This way, the normal TQt widgets can be used as
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overlays for fancy effects: just create a palette for them with the
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transparent color for the wanted color roles, e.g. Background and
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Base, in the Normal and/or Active modes. This way, you can create
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see-through TQPushButtons etc.
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