forked from AuroraMiddleware/gtk
docs: Refresh the "Q & A" part
Remove references to long-gone API, add some pointers to more modern alternatives, etc.
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Matthias Clasen
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@ -47,8 +47,7 @@ this reference manual for details.
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<qandaentry>
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<question><para>
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Where can I get help with GTK, submit a bug report, or make a feature
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request?
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Where can I get help with GTK, submit a bug report, or make a feature request?
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</para></question>
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<answer>
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@ -63,13 +62,14 @@ See the <link linkend="gtk-resources">documentation on this topic</link>.
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<qandaentry>
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<question><para>How do I port from one GTK
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version to another?</para></question>
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<question><para>
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How do I port from one GTK version to another?
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</para></question>
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<answer>
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<para>
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See <xref linkend="gtk-migrating-2-to-3"/>.
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See <xref linkend="migrating"/>.
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You may also find useful information in the documentation for
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specific widgets and functions.
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</para>
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@ -88,8 +88,7 @@ against the documentation.
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<qandaentry>
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<question><para>
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How does memory management work in GTK? Should I free data returned
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from functions?
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How does memory management work in GTK? Should I free data returned from functions?
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</para></question>
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<answer>
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@ -528,10 +527,9 @@ the call away if it appears that the value is not being used.
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</para>
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<para>
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A common workaround for this problem is to store the result in a volatile
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variable, which keeps the compiler from optimizing the call away.
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GLib provides the g_type_ensure() function to work around this problem.
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<informalexample><programlisting>
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volatile GType dummy = GTK_TYPE_BLAH;
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g_type_ensure (GTK_TYPE_BLAH);
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</programlisting></informalexample>
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</para>
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</answer>
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@ -546,32 +544,9 @@ How do I create a transparent toplevel window ?
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<answer>
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<para>
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To make a window transparent, it needs to use a visual which supports that.
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This is done by getting the RGBA visual of the screen with
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gdk_screen_get_rgba_visual() and setting it on the window. Note that
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gdk_screen_get_rgba_visual() will return %NULL if transparent windows
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are not supported on the screen, you should fall back to
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gdk_screen_get_system_visual() in that case. Additionally, note that this
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will change from screen to screen, so it needs to be repeated whenever the
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window is moved to a different screen.
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<informalexample><programlisting>
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GdkVisual *visual;
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visual = gdk_screen_get_rgba_visual (screen);
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if (visual == NULL)
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visual = gdk_screen_get_system_visual (screen);
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gtk_widget_set_visual (GTK_WIDGET (window), visual);
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</programlisting></informalexample>
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To fill the alpha channel on the window simply use cairos
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RGBA drawing capabilities.
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</para>
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<para>
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Note that the presence of an RGBA visual is no guarantee that the
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window will actually appear transparent on screen. On X11, this
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requires a compositing manager to be running. See
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gdk_display_is_composited() for a way to find out if the alpha
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channel will be respected.
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Any toplevel window can be transparent.
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It is just a matter of setting a transparent background
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in the CSS style for it.
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</para>
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</answer>
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</qandaentry>
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@ -587,9 +562,19 @@ channel will be respected.
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<answer>
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<para>
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See <link linkend="TreeWidget">tree widget overview</link> — you
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should use the #GtkTreeView widget. (A list is just a tree with no branches,
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so the tree widget is used for lists as well).
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This question has different answers, depending on the size of the dataset
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and the required formatting flexibility.
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</para>
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<para>
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If you want to display a large amount of data in a uniform way, your
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best option is a #GtkTreeView widget. See <link linkend="TreeWidget">tree
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widget overview</link>. A list is just a tree with no branches, so the treeview
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widget is used for lists as well.
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</para>
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<para>
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If you want to display a small amount of items, but need flexible formatting
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and widgetry inside the list, then you probably want to use a #GtkListBox,
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which uses regular widgets for display.
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</para>
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</answer>
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</qandaentry>
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@ -620,7 +605,11 @@ single-line text entry, see #GtkEntry.
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<answer>
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<para>
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#GtkImage can display images in just about any format GTK understands.
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GTK has two widgets that are dedicated to displaying images. #GtkImage, for
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small, fixed-size icons and #GtkPicture for content images.
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</para>
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<para>
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Both can display images in just about any format GTK understands.
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You can also use #GtkDrawingArea if you need to do something more complex,
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such as draw text or graphics over the top of the image.
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</para>
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@ -653,9 +642,10 @@ How do I change the color of a widget?
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</para></question>
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<answer><para>
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See gtk_widget_override_color() and gtk_widget_override_background_color().
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You can also change the appearance of a widget by installing a
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custom style provider, see gtk_style_context_add_provider().
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The background color of a widget is determined by the CSS style that applies
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to it. To change that, you can set style classes on the widget, and provide
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custom CSS to change the appearance. Such CSS can be loaded with
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gtk_css_provider_load_from_file() and its variants. See gtk_style_context_add_provider().
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</para></answer>
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</qandaentry>
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@ -665,16 +655,6 @@ How do I change the font of a widget?
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</para></question>
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<answer><para>
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This has several possible answers, depending on what exactly you want to
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achieve. One option is gtk_widget_override_font().
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<informalexample><programlisting>
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PangoFontDesc *font_desc = pango_font_description_new (<!-- -->);
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pango_font_description_set_size (font_desc, 40);
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gtk_widget_override_font (widget, font);
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pango_font_description_free (font_desc);
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</programlisting></informalexample>
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</para>
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<para>
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If you want to make the text of a label larger, you can use
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gtk_label_set_markup():
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<informalexample><programlisting>
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@ -939,32 +919,28 @@ How do I use cairo to draw in GTK applications ?
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</para></question>
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<answer><para>
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The #GtkWidget::draw signal gets a ready-to-use cairo context
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as parameter that you should use.
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</para>
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<para>
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All drawing in GTK is normally done in a draw handler, and GTK
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creates a temporary pixmap for double-buffering the drawing.
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It is possible to turn off double-buffering, with
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gtk_widget_set_double_buffered(), but this is not ideal,
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since it can cause some flickering.
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Use gtk_snapshot_append_cairo() in your #GtkWidget::snapshot signal handler
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to optain a cairo context and draw with that.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question><para>
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Can I improve the performance of my application by using the
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Glitz or GL backend of cairo ?
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Can I improve the performance of my application by using another backend
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of cairo (such as GL) ?
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</para></question>
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<answer><para>
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No. The GDK X11 backend uses the cairo X backend (and the other
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GDK backends use their respective native cairo backends). The
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GTK developers believe that the best way to improving the GDK
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drawing performance is to optimize the cairo X backend and the
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relevant code paths in the X server that is uses (mostly the
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Render extension).
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No. Most drawing in GTK is not done via cairo anymore (but instead
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by the GL or Vulkan renderers of GSK).
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</para>
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<para>
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If you use cairo for drawing your own widgets, gtk_snapshot_append_cairo()
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will choose the most appropriate surface type for you.
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</para>
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<para>
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If you are interested in using GL for your own drawing, see #GtkGLArea.
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</para></answer>
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</qandaentry>
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@ -974,8 +950,11 @@ Can I use cairo to draw on a #GdkPixbuf ?
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</para></question>
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<answer><para>
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No, at least not yet. The cairo image surface does not support the
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pixel format used by GdkPixbuf.
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No. The cairo image surface does not support the pixel format used by GdkPixbuf.
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</para>
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<para>
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If you need to get cairo drawing into a format that can be displayed efficiently
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by GTK, you may want to use an image surface and gdk_memory_texture_new().
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</para></answer>
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</qandaentry>
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