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<div class="example">
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<a name="composited-window-example"></a><p class="title"><b>Example 7. Composited windows</b></p>
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<div class="example-contents">
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<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
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<td class="listing_lines" align="right"><pre>1
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<td class="listing_code"><pre class="programlisting"><span class="preproc">#include </span><span class="number"><gtk/gtk.h></span>
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<span class="comment">/*</span><span class="comment"> The expose event handler for the event box.</span>
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<span class="comment"> *</span>
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<span class="comment"> * This function simply draws a transparency onto a widget on the area</span>
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<span class="comment"> * for which it receives expose events. This is intended to give the</span>
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<span class="comment"> * event box a "transparent" background.</span>
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<span class="comment"> *</span>
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<span class="comment"> * In order for this to work properly, the widget must have an RGBA</span>
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<span class="comment"> * colourmap. The widget should also be set as app-paintable since it</span>
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<span class="comment"> * doesn't make sense for GTK+ to draw a background if we are drawing it</span>
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<span class="comment"> * (and because GTK+ might actually replace our transparency with its</span>
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<span class="comment"> * default background colour).</span>
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<span class="comment"> </span><span class="comment">*/</span>
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<span class="type">static</span> gboolean
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<div class="example-contents"><pre class="programlisting">
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#include <gtk/gtk.h>
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/* The expose event handler for the event box.
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* This function simply draws a transparency onto a widget on the area
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* for which it receives expose events. This is intended to give the
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* event box a "transparent" background.
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* In order for this to work properly, the widget must have an RGBA
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* colourmap. The widget should also be set as app-paintable since it
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* doesn't make sense for GTK+ to draw a background if we are drawing it
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* (and because GTK+ might actually replace our transparency with its
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* default background colour).
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transparent_expose (GtkWidget *widget,
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GdkEventExpose *event)
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gdk_cairo_region (cr, event->region);
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cairo_destroy (cr);
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<span class="keyword">return</span> FALSE;
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<span class="comment">/*</span><span class="comment"> The expose event handler for the window.</span>
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<span class="comment"> *</span>
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<span class="comment"> * This function performs the actual compositing of the event box onto</span>
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<span class="comment"> * the already-existing background of the window at 50% normal opacity.</span>
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<span class="comment"> *</span>
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<span class="comment"> * In this case we do not want app-paintable to be set on the widget</span>
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<span class="comment"> * since we want it to draw its own (red) background. Because of this,</span>
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<span class="comment"> * however, we must ensure that we use g_signal_connect_after so that</span>
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<span class="comment"> * this handler is called after the red has been drawn. If it was</span>
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<span class="comment"> * called before then GTK would just blindly paint over our work.</span>
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<span class="comment"> *</span>
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<span class="comment"> * Note: if the child window has children, then you need a cairo 1.6</span>
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<span class="comment"> * feature to make this work correctly.</span>
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<span class="comment"> </span><span class="comment">*/</span>
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<span class="type">static</span> gboolean
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/* The expose event handler for the window.
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* This function performs the actual compositing of the event box onto
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* the already-existing background of the window at 50% normal opacity.
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* In this case we do not want app-paintable to be set on the widget
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* since we want it to draw its own (red) background. Because of this,
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* however, we must ensure that we use g_signal_connect_after so that
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* this handler is called after the red has been drawn. If it was
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* called before then GTK would just blindly paint over our work.
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* Note: if the child window has children, then you need a cairo 1.6
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* feature to make this work correctly.
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window_expose_event (GtkWidget *widget,
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GdkEventExpose *event)
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GdkRegion *region;
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GtkWidget *child;
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<span class="comment">/*</span><span class="comment"> get our child (in this case, the event box) </span><span class="comment">*/</span>
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/* get our child (in this case, the event box) */
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child = gtk_bin_get_child (GTK_BIN (widget));
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<span class="comment">/*</span><span class="comment"> create a cairo context to draw to the window </span><span class="comment">*/</span>
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/* create a cairo context to draw to the window */
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cr = gdk_cairo_create (widget->window);
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<span class="comment">/*</span><span class="comment"> the source data is the (composited) event box </span><span class="comment">*/</span>
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/* the source data is the (composited) event box */
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gdk_cairo_set_source_pixmap (cr, child->window,
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child->allocation.x,
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child->allocation.y);
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<span class="comment">/*</span><span class="comment"> draw no more than our expose event intersects our child </span><span class="comment">*/</span>
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/* draw no more than our expose event intersects our child */
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region = gdk_region_rectangle (&child->allocation);
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gdk_region_intersect (region, event->region);
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gdk_cairo_region (cr, region);
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<span class="comment">/*</span><span class="comment"> composite, with a 50% opacity </span><span class="comment">*/</span>
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/* composite, with a 50% opacity */
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cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
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cairo_paint_with_alpha (cr, <span class="number">0.5</span>);
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<span class="comment">/*</span><span class="comment"> we're done </span><span class="comment">*/</span>
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cairo_paint_with_alpha (cr, 0.5);
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cairo_destroy (cr);
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<span class="keyword">return</span> FALSE;
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<span class="type">int</span>
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main (<span class="type">int</span> argc, <span class="type">char</span> **argv)
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main (int argc, char **argv)
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GtkWidget *window, *event, *button;
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GdkScreen *screen;
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GdkColormap *rgba;
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gtk_init (&argc, &argv);
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<span class="comment">/*</span><span class="comment"> Make the widgets </span><span class="comment">*/</span>
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button = gtk_button_new_with_label (<span class="number">"A Button"</span>);
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/* Make the widgets */
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button = gtk_button_new_with_label ("A Button");
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event = gtk_event_box_new ();
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window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
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<span class="comment">/*</span><span class="comment"> Put a red background on the window </span><span class="comment">*/</span>
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gdk_color_parse (<span class="number">"red"</span>, &red);
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/* Put a red background on the window */
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gdk_color_parse ("red", &red);
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gtk_widget_modify_bg (window, GTK_STATE_NORMAL, &red);
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<span class="comment">/*</span><span class="comment"> Set the colourmap for the event box.</span>
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<span class="comment"> * Must be done before the event box is realised.</span>
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<span class="comment"> </span><span class="comment">*/</span>
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/* Set the colourmap for the event box.
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* Must be done before the event box is realised.
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screen = gtk_widget_get_screen (event);
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rgba = gdk_screen_get_rgba_colormap (screen);
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gtk_widget_set_colormap (event, rgba);
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<span class="comment">/*</span><span class="comment"> Set our event box to have a fully-transparent background</span>
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<span class="comment"> * drawn on it. Currently there is no way to simply tell GTK+</span>
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<span class="comment"> * that "transparency" is the background colour for a widget.</span>
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<span class="comment"> </span><span class="comment">*/</span>
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/* Set our event box to have a fully-transparent background
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* drawn on it. Currently there is no way to simply tell GTK+
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* that "transparency" is the background colour for a widget.
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gtk_widget_set_app_paintable (GTK_WIDGET (event), TRUE);
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g_signal_connect (event, <span class="number">"expose-event"</span>,
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G_CALLBACK (transparent_expose), <span class="number">NULL</span>);
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<span class="comment">/*</span><span class="comment"> Put them inside one another </span><span class="comment">*/</span>
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gtk_container_set_border_width (GTK_CONTAINER (window), <span class="number">10</span>);
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g_signal_connect (event, "expose-event",
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G_CALLBACK (transparent_expose), NULL);
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/* Put them inside one another */
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gtk_container_set_border_width (GTK_CONTAINER (window), 10);
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gtk_container_add (GTK_CONTAINER (window), event);
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gtk_container_add (GTK_CONTAINER (event), button);
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<span class="comment">/*</span><span class="comment"> Realise and show everything </span><span class="comment">*/</span>
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/* Realise and show everything */
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gtk_widget_show_all (window);
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<span class="comment">/*</span><span class="comment"> Set the event box GdkWindow to be composited.</span>
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<span class="comment"> * Obviously must be performed after event box is realised.</span>
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<span class="comment"> </span><span class="comment">*/</span>
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/* Set the event box GdkWindow to be composited.
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* Obviously must be performed after event box is realised.
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gdk_window_set_composited (event->window, TRUE);
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<span class="comment">/*</span><span class="comment"> Set up the compositing handler.</span>
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<span class="comment"> * Note that we do _after_ so that the normal (red) background is drawn</span>
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<span class="comment"> * by gtk before our compositing occurs.</span>
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<span class="comment"> </span><span class="comment">*/</span>
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g_signal_connect_after (window, <span class="number">"expose-event"</span>,
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G_CALLBACK (window_expose_event), <span class="number">NULL</span>);
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/* Set up the compositing handler.
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* Note that we do _after_ so that the normal (red) background is drawn
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* by gtk before our compositing occurs.
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g_signal_connect_after (window, "expose-event",
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G_CALLBACK (window_expose_event), NULL);
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<span class="keyword">return</span> <span class="number">0</span>;
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<br class="example-break"><p>
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In the example <a class="xref" href="gdk-Windows.html#composited-window-example" title="Example 7. Composited windows">Example 7, “Composited windows”</a>, a button is
added
removed
docs/reference/gdk/html/gdk-Windows.html
