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Update information about visuals

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Based on a patch by Jasper St. Pierre,
https://bugzilla.gnome.org/show_bug.cgi?id=639520
This commit is contained in:
Matthias Clasen 2011-01-14 20:45:53 -05:00
parent 8f6a8441a2
commit d790fd4fdd
1 changed files with 14 additions and 13 deletions
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27
docs/reference/gtk/question_index.sgml
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@ -547,23 +547,24 @@ How do I create a transparent toplevel window ?
<answer>
<para>
To make a window transparent, it needs to use a visual which supports that.
This is done by getting the RGBA colormap of the screen with
gdk_screen_get_rgba_colormap() and setting it on the window. Note that
gdk_screen_get_rgba_colormap() will return %NULL if transparent windows
are not supported on the screen; also note that this may change from
screen to screen, so it needs to be repeated whenever the window is moved
to a different screen.
This is done by getting the RGBA visual of the screen with
gdk_screen_get_rgba_visual() and setting it on the window. Note that
gdk_screen_get_rgba_visual() will return %NULL if transparent windows
are not supported on the screen, you should fall back to
gdk_screen_get_system_visual() in that case. Additionally, note that this
will change from screen to screen, so it needs to be repeated whenever the
window is moved to a different screen.
<informalexample><programlisting>
GdkColormap *colormap;
GdkVisual *visual;
colormap = gdk_screen_get_rgba_colormap (screen);
if (!colormap)
colormap = gdk_screen_get_rgb_colormap (screen);
visual = gdk_screen_get_rgba_visual (screen);
if (visual == NULL)
visual = gdk_screen_get_system_visual (screen);
gtk_widget_set_colormap (widget, colormap);
gtk_widget_set_visual (GTK_WIDGET (window), visual);
</programlisting></informalexample>
One possibility to fill the alpha channel on the window is to use
gdk_draw_rgb_32_image().
To fill the alpha channel on the window simply use cairos
RGBA drawing capabilities.
</para>
<para>
Note that the presence of an RGBA visual is no guarantee that the