Commit d69ba207 authored by Matthias Clasen's avatar Matthias Clasen Committed by Matthias Clasen

Add some questions.

2006-06-21  Matthias Clasen  <mclasen@redhat.com>

	* gtk/question_index.sgml: Add some questions.
parent edee48fb
2006-06-21 Matthias Clasen <mclasen@redhat.com>
* gtk/question_index.sgml: Add some questions.
2006-06-20 Matthias Clasen <mclasen@redhat.com>
* gtk/gtk-sections.txt: Remove unused print-to-file setting
......
......@@ -524,6 +524,38 @@ volatile GType dummy = GTK_TYPE_BLAH;
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
How do I create a transparent toplevel window ?
</para>
</question>
<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.
<informalexample><programlisting>
GdkColormap *colormap;
colormap = gdk_screen_get_rgba_colormap (screen);
if (!colormap)
colormap = gtk_screen_get_rgb_colormap (screen);
gtk_widget_set_colormap (widget, colormap);
</programlisting></informalexample>
One possibility to fill the alpha channel on the window is to use
gdk_draw_rgb_32_image().
</para>
</answer>
</qandaentry>
</qandadiv>
<qandadiv><title>Which widget should I use...</title>
......@@ -892,6 +924,83 @@ See gtk_tree_view_set_expander_column() and gtk_tree_view_column_set_visible().
</qandadiv>
<qandadiv><title>Using cairo with GTK+</title>
<qandaentry>
<question><para>
How do I use cairo to draw in GTK+ applications ?
</para></question>
<answer><para>
USe gdk_cairo_create() to obtain a cairo context for drawing
on a GDK window or pixmap. See <link linkend="gdk-Cairo-Interaction">Cairo
Interaction</link> for some more useful functions.
</para></answer>
</qandaentry>
<qandaentry>
<question><para>
I have created a cairo context with gdk_cairo_create(), but when I
later use it, my drawing does not show up. Why is that ?
</para></question>
<answer>
<para>
All drawing in GTK+ is normally done in an expose handler, and GTK+
creates a temporary pixmap for double-buffering the drawing. If you
create a cairo context outside the expose handler, it is backed
by the GDK window itself, not the double-buffering pixmap. Consequently,
any drawing you do with that cairo context gets overwritten at the
end of the expose handler, when the double-buffering pixmap is copied
back.
</para>
<para>
Possible solutions to this problem are:
<itemizedlist>
<listitem><para>
Turn off double-buffering, with gtk_widget_set_double_buffered().
This is not ideal, since it can cause some flickering.
</para></listitem>
<listitem><para>
Create the cairo context inside the expose handler. If you do this,
gdk_create_cairo() arranges for it to be backed by the double-buffering
pixmap. This is the preferred solution, and is used throughout GTK+
itself.
</para></listitem>
</itemizedlist>
</para>
</answer>
</qandaentry>
<qandaentry>
<question><para>
Can I improve the performance of my application by using the
Glitz backend of cairo ?
</para></question>
<answer><para>
No. The GDK X11 backend uses the cairo X backend (and the other
GDK backends use their respective native cairo backends). The
GTK+ developers believe that the best way to improving the GDK
drawing performance is to optimize the cairo X backend and the
relevant code paths in the X server that is uses (mostly the
Render extension).
</para></answer>
</qandaentry>
<qandaentry>
<question><para>
Can I use cairo to draw on a #GdkPixbuf ?
</para></question>
<answer><para>
No, at least not yet. The cairo image surface does not support the
pixel format used by GdkPixbuf.
</para></answer>
</qandaentry>
</qandadiv>
</qandaset>
</refsect1>
......
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