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<chapter id="gtk-migrating-GtkStyleContext">
<title>Theming changes</title>
<para>
In GTK+ 3.0, #GtkStyleContext was added to replace #GtkStyle and
the theming infrastructure available in 2.x. GtkStyleContext is an
object similar in spirit to GtkStyle, as it contains theming information,
although in a more complete and tokenized fashion. There are two aspects
to switching to GtkStyleContext: porting themes and theme engines, and
porting applications, libraries and widgets.
</para>
<section id="gtk-migrating-GtkStyleContext-themes">
<title>Migrating themes</title>
<para>
From GTK+ 3.0 on, theme engines must implement #GtkThemingEngine and be
installed in <filename>$libdir/gtk+-3.0/$GTK_VERSION/theming-engines</filename>,
and the files containing style information must be written in the CSS-like
format that is understood by #GtkCssProvider. For a theme named
"Clearlooks", the CSS file parsed by default is
<filename>$datadir/themes/Clearlooks/gtk-3.0/gtk.css</filename>,
with possible variants such as the dark theme being named
<filename>gtk-dark.css</filename> in the same directory.
</para>
<para>
If your theme RC file was providing values for #GtkSettings, you
can install a <filename>settings.ini</filename> keyfile along with
the <filename>gtk.css</filename> to provide theme-specific defaults
for settings.
</para>
<para>
Key themes have been converted to CSS syntax too. See the
<link linkend="css-binding-set">GtkCssProvider</link> documentation
information about the syntax. GTK+ looks for key themes in the file
<filename>$datadir/themes/<replaceable>theme</replaceable>/gtk-3.0/gtk-keys.css</filename>, where <replaceable>theme</replaceable> is the current
key theme name.
</para>
</section>
<section id="gtk-migrating-theme-GtkStyleContext-engines">
<title>Migrating theme engines</title>
<para>
Migrating a #GtkStyle based engine to a #GtkThemingEngine based one
should be straightforward for most of the vfuncs. Besides a cleanup
in the available paint methods and a simplification in the passed
arguments (in favor of #GtkStyleContext containing all the information),
the available render methods resemble those of #GtkStyle quite
evidently. Notable differences include:
</para>
<orderedlist>
<listitem>
All variations of gtk_paint_box(), gtk_paint_flat_box(),
gtk_paint_shadow(), gtk_paint_box_gap() and gtk_paint_shadow_gap()
are replaced by gtk_render_background(), gtk_render_frame() and
gtk_render_frame_gap(). The first function renders frameless
backgrounds and the last two render frames in various forms.
</listitem>
<listitem>
gtk_paint_resize_grip() has been subsumed by gtk_render_handle()
with a #GTK_STYLE_CLASS_GRIP class set in the style context.
</listitem>
<listitem>
gtk_paint_spinner() disappears in favor of gtk_render_activity()
with a #GTK_STYLE_CLASS_SPINNER class set in the style context.
</listitem>
</orderedlist>
<para>
The list of available render methods is:
</para>
<simplelist>
<member>
gtk_render_background(): Renders a widget/area background.
</member>
<member>
gtk_render_frame(): Renders a frame border around the given rectangle.
Usually the detail of the border depends on the theme information,
plus the current widget state.
</member>
<member>
gtk_render_frame_gap(): Renders a frame border with a gap on one side.
</member>
<member>
gtk_render_layout(): Renders a #PangoLayout.
</member>
<member>
gtk_render_handle(): Renders all kind of handles and resize grips,
depending on the style class.
</member>
<member>
gtk_render_check(): Render checkboxes.
</member>
<member>
gtk_render_option(): Render radiobuttons.
</member>
<member>
gtk_render_arrow(): Renders an arrow pointing to a direction.
</member>
<member>
gtk_render_expander(): Renders an expander indicator, such as in
#GtkExpander.
</member>
<member>
gtk_render_focus(): Renders the indication that a widget has the
keyboard focus.
</member>
<member>
gtk_render_line(): Renders a line from one coordinate to another.
</member>
<member>
gtk_render_slider(): Renders a slider, such as in #GtkScale.
</member>
<member>
gtk_render_extension(): Renders an extension that protrudes from
a UI element, such as a notebook tab.
</member>
<member>
gtk_render_activity(): Renders an area displaying activity, be it
a progressbar or a spinner.
</member>
<member>
gtk_render_icon_pixbuf(): Renders an icon into a #GdkPixbuf.
</member>
</simplelist>
<para>
One of the main differences to #GtkStyle<!-- -->-based engines is that the
rendered widget is totally isolated from the theme engine, all style
information is meant to be retrieved from the #GtkThemingEngine API,
or from the #GtkWidgetPath obtained from gtk_theming_engine_get_path(),
which fully represents the rendered widget's hierarchy from a styling
point of view.
</para>
<para>
The detail string available in #GtkStyle<!-- -->-based engines has been
replaced by widget regions and style classes. Regions are a way for
complex widgets to associate different styles with different areas,
such as even and odd rows in a treeview. Style classes allow sharing
of style information between widgets, regardless of their type.
Regions and style classes can be used in style sheets to associate
styles, and them engines can also access them. There are several
predefined classes and regions such as %GTK_STYLE_CLASS_BUTTON or
%GTK_STYLE_REGION_TAB in <filename>gtkstylecontext.h</filename>,
although custom widgets may define their own, which themes may
attempt to handle.
</para>
</section>
<section id="gtk-migrating-GtkStyleContext-parser-extensions">
<title>Extending the CSS parser</title>
<para>
In #GtkStyle<!-- -->-based engines, GtkRCStyle provided ways to extend the
gtkrc parser with engine-specific extensions. This has been replaced
by gtk_theming_engine_register_property(), which lets a theme engine
register new properties with an arbitrary type. While there is built-in
support for most basic types, it is possible to use a custom parser
for the property.
</para>
<para>
The installed properties depend on the #GtkThemingEngine:name property,
so they should be added in the <literal>constructed()</literal> vfunc.
For example, if an engine with the name "Clearlooks" installs a
"focus-color" property with the type #GdkRGBA, the property
<literal>-Clearlooks-focus-color</literal> will be registered and
accepted in CSS like this:
<informalexample><programlisting>
GtkEntry {
-Clearlooks-focus-color: rgba(255, 0, 0, 1.0);
}
</programlisting></informalexample>
</para>
<para>
Widget style properties also follow a similar syntax, with the widget
type name used as a prefix. For example, the #GtkWidget focus-line-width
style property can be modified in CSS as
<literal>-GtkWidget-focus-line-width</literal>.
</para>
</section>
<section id="gtk-migrating-GtkStyleContext-css">
<title>Using the CSS file format</title>
<para>
The syntax of RC and CSS files formats is obviously different.
The CSS-like syntax will hopefully be much more familiar to many
people, lowering the barrier for custom theming.
</para>
<para>
Instead of going through the syntax differences one-by-one, we
will present a more or less comprehensive example and discuss
how it can be translated into CSS:
</para>
<example>
<title>Sample RC code</title>
<programlisting>
style "default" {
xthickness = 1
ythickness = 1
GtkButton::child-displacement-x = 1
GtkButton::child-displacement-y = 1
GtkCheckButton::indicator-size = 14
bg[NORMAL] = @bg_color
bg[PRELIGHT] = shade (1.02, @bg_color)
bg[SELECTED] = @selected_bg_color
bg[INSENSITIVE] = @bg_color
bg[ACTIVE] = shade (0.9, @bg_color)
fg[NORMAL] = @fg_color
fg[PRELIGHT] = @fg_color
fg[SELECTED] = @selected_fg_color
fg[INSENSITIVE] = darker (@bg_color)
fg[ACTIVE] = @fg_color
text[NORMAL] = @text_color
text[PRELIGHT] = @text_color
text[SELECTED] = @selected_fg_color
text[INSENSITIVE] = darker (@bg_color)
text[ACTIVE] = @selected_fg_color
base[NORMAL] = @base_color
base[PRELIGHT] = shade (0.95, @bg_color)
base[SELECTED] = @selected_bg_color
base[INSENSITIVE] = @bg_color
base[ACTIVE] = shade (0.9, @selected_bg_color)
engine "clearlooks" {
colorize_scrollbar = TRUE
style = CLASSIC
}
}
style "tooltips" {
xthickness = 4
ythickness = 4
bg[NORMAL] = @tooltip_bg_color
fg[NORMAL] = @tooltip_fg_color
}
style "button" {
xthickness = 3
ythickness = 3
bg[NORMAL] = shade (1.04, @bg_color)
bg[PRELIGHT] = shade (1.06, @bg_color)
bg[ACTIVE] = shade (0.85, @bg_color)
}
style "entry" {
xthickness = 3
ythickness = 3
bg[SELECTED] = mix (0.4, @selected_bg_color, @base_color)
fg[SELECTED] = @text_color
engine "clearlooks" {
focus_color = shade (0.65, @selected_bg_color)
}
}
style "other" {
bg[NORMAL] = #fff;
}
class "GtkWidget" style "default"
class "GtkEntry" style "entry"
widget_class "*<GtkButton>" style "button"
widget "gtk-tooltip*" style "tooltips"
widget_class "window-name.*.GtkButton" style "other"
</programlisting>
</example>
<para>
would roughly translate to this CSS:
</para>
<example>
<title>CSS translation</title>
<programlisting>
* {
padding: 1;
-GtkButton-child-displacement-x: 1;
-GtkButton-child-displacement-y: 1;
-GtkCheckButton-indicator-size: 14;
background-color: @bg_color;
color: @fg_color;
-Clearlooks-colorize-scrollbar: true;
-Clearlooks-style: classic;
}
*:hover {
background-color: shade (@bg_color, 1.02);
}
*:selected {
background-color: @selected_bg_color;
color: @selected_fg_color;
}
*:insensitive {
color: shade (@bg_color, 0.7);
}
*:active {
background-color: shade (@bg_color, 0.9);
}
.tooltip {
padding: 4;
background-color: @tooltip_bg_color;
color: @tooltip_fg_color;
}
.button {
padding: 3;
background-color: shade (@bg_color, 1.04);
}
.button:hover {
background-color: shade (@bg_color, 1.06);
}
.button:active {
background-color: shade (@bg_color, 0.85);
}
.entry {
padding: 3;
background-color: @base_color;
color: @text_color;
}
.entry:selected {
background-color: mix (@selected_bg_color, @base_color, 0.4);
-Clearlooks-focus-color: shade (0.65, @selected_bg_color)
}
/* The latter selector is an specification of the first,
since any widget may use the same classes or names */
#window-name .button,
GtkWindow#window-name GtkButton.button {
background-color: #fff;
}
</programlisting>
</example>
<para>
One notable difference is the reduction from fg/bg/text/base colors
to only foreground/background, in exchange the widget is able to render
its various elements with different CSS classes, which can be themed
independently.
</para>
<para>
In the same vein, the light, dark and mid color variants that
were available in GtkStyle should be replaced by a combination of
symbolic colors and custom CSS, where necessary. text_aa should
really not be used anywhere, anyway, and the white and black colors
that were available in GtkStyle can just be replaced by literal
GdkRGBA structs.
</para>
<para>
Access to colors has also changed a bit. With #GtkStyle, the common
way to access colors is:
<informalexample><programlisting>
GdkColor *color1;
GdkColor color2;
color1 = &style->bg[GTK_STATE_PRELIGHT];
gtk_style_lookup_color (style, "focus_color", &color2);
</programlisting></informalexample>
With #GtkStyleContext, you generally use #GdkRGBA instead of #GdkColor
and the code looks like this:
<informalexample><programlisting>
GdkRGBA *color1;
GdkRGBA color2;
gtk_style_context_get (context, GTK_STATE_FLAG_PRELIGHT,
"background-color", &color1,
NULL);
gtk_style_context_lookup_color (context, "focus_color", &color2);
...
gdk_rgba_free (color1);
</programlisting></informalexample>
Note that the memory handling here is different: gtk_style_context_get()
expects the address of a GdkRGBA* and returns a newly allocated struct,
gtk_style_context_lookup_color() expects the address of an existing
struct, and fills it.
</para>
<para>
It is worth mentioning that the new file format does not support
stock icon mappings as the RC format did.
</para>
</section>
<section id="gtk-migrating-GtkStyleContext-checklist">
<title>A checklist for widgets</title>
<para>
When porting your widgets to use #GtkStyleContext, this checklist
might be useful.
</para>
<orderedlist>
<listitem>
Replace #GtkWidget::style-set handlers with
#GtkWidget::style-updated handlers.
</listitem>
<listitem>
<para>
Try to identify the role of what you're rendering with any number
of classes. This will replace the detail string. There is a predefined
set of CSS classes which you can reuse where appropriate. Doing so
will give you theming 'for free', whereas custom classes will require
extra work in the theme. Note that complex widgets are likely to
need different styles when rendering different parts, and style
classes are one way to achieve this. This could result in code like
the following (simplified) examples:
</para>
<example>
<title>Setting a permanent CSS class</title>
<programlisting>
static void
gtk_button_init (GtkButton *button)
{
GtkStyleContext *context;
...
context = gtk_widget_get_style_context (GTK_WIDGET (button));
/* Set the "button" class */
gtk_style_context_add_class (context, GTK_STYLE_CLASS_BUTTON);
}
</programlisting>
</example>
<para>
Or
</para>
<example>
<title>Using dynamic CSS classes for different elements</title>
<programlisting>
static gboolean
gtk_spin_button_draw (GtkSpinButton *spin,
cairo_t *cr)
{
GtkStyleContext *context;
...
context = gtk_widget_get_style_context (GTK_WIDGET (spin));
gtk_style_context_save (context);
gtk_style_context_add_class (context, GTK_STYLE_CLASS_ENTRY);
/* Call to entry draw impl with "entry" class */
parent_class->draw (spin, cr);
gtk_style_context_restore (context);
gtk_style_context_save (context);
/* Render up/down buttons with the "button" class */
gtk_style_context_add_class (context, GTK_STYLE_CLASS_BUTTON);
draw_up_button (spin, cr);
draw_down_button (spin, cr);
gtk_style_context_restore (context);
...
}
</programlisting>
</example>
<para>
Note that #GtkStyleContext only provides fg/bg colors, so text/base
is done through distinctive theming of the different classes. For
example, an entry would usually be black on white while a button
would usually be black on light grey.
</para>
</listitem>
<listitem>
<para>
Replace all <literal>gtk_paint_*()</literal> calls with corresponding
<literal>gtk_render_*()</literal> calls.
</para>
<para>
The most distinctive changes are the use of #GtkStateFlags to
represent the widget state and the lack of #GtkShadowType. Note
that widget state is now passed implicitly via the context, so
to render in a certain state, you have to temporarily set the
state on the context, as in the following example:
</para>
<example>
<title>Rendering with a specific state</title>
<programlisting>
gtk_style_context_save (context);
gtk_style_context_set_state (context, GTK_STATE_FLAG_ACTIVE);
gtk_render_check (context, cr, x, y, width, height);
gtk_style_context_restore (context);
</programlisting>
</example>
<para>
For gtk_render_check() and gtk_render_option(), the @shadow_type
parameter is replaced by the #GTK_STATE_FLAG_ACTIVE and
#GTK_STATE_FLAG_INCONSISTENT state flags. For things such as
pressed/unpressed button states, #GTK_STATE_FLAG_ACTIVE is used,
and the CSS may style normal/active states differently to render
outset/inset borders, respectively.
</para>
</listitem>
<listitem>
The various <literal>gtk_widget_modify_*()</literal> functions to
override colors or fonts for individual widgets have been replaced
by similar <literal>gtk_widget_override_*()</literal> functions.
</listitem>
<listitem>
It is no longer necessary to call gtk_widget_style_attach(),
gtk_style_attach(), gtk_style_detach() or gtk_widget_ensure_style().
</listitem>
<listitem>
Replace all uses of xthickness/ythickness. #GtkStyleContext uses the
CSS box model, and there are border-width/padding/margin properties to
replace the different applications of X and Y thickness. Note that all
of this is merely a guideline. Widgets may choose to follow it or not.
</listitem>
</orderedlist>
</section>
<section id="gtk-migrating-GtkStyleContext-parsing">
<title>Parsing of custom resources</title>
<para>
As a consequence of the RC format going away, calling gtk_rc_parse() or
gtk_rc_parse_string() won't have any effect on a widgets appearance.
The way to replace these calls is using a custom #GtkStyleProvider,
either for an individual widget through gtk_style_context_add_provider()
or for all widgets on a screen through gtk_style_context_add_provider_for_screen().
Typically, the provider will be a #GtkCssProvider, which parse CSS
information from a file or from a string.
</para>
<example>
<title>Using a custom GtkStyleProvider</title>
<programlisting>
GtkStyleContext *context;
GtkCssProvider *provider;
context = gtk_widget_get_style_context (widget);
provider = gtk_css_provider_new ();
gtk_css_provider_load_from_data (GTK_CSS_PROVIDER (provider),
".frame1 {\n"
" border-image: url('gradient1.png') 10 10 10 10 stretch;\n"
"}\n", -1, NULL);
gtk_style_context_add_provider (context,
GTK_STYLE_PROVIDER (provider),
GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
g_object_unref (provider);
</programlisting>
</example>
<para>
Notice that you can also get style information from custom resources
by implementing the #GtkStyleProvider interface yourself. This is
an advanced feature that should be rarely used.
</para>
</section>
<section id="gtk-migrating-GtkStyleContext-bonus-points">
<title>Bonus points</title>
<para>
There are some features in #GtkStyleContext that were not available in
#GtkStyle, or were made available over time for certain widgets through
extending the detail string in obscure ways. There is a lot more
information available when rendering UI elements, and it is accessible
in more uniform, less hacky ways. By going through this list you'll
ensure your widget is a good citizen in a fully themable user interface.
</para>
<orderedlist>
<listitem>
If your widget renders a series of similar elements, such as tabs
in a #GtkNotebook or rows/column in a #GtkTreeView, consider adding
regions through gtk_style_context_add_region(). These regions can be
referenced in CSS and the :nth-child pseudo-class may be used to match
the elements depending on the flags passed.
<example>
<title>Theming widget regions</title>
<programlisting>
GtkNotebook tab {
background-color: #f3329d;
}
GtkTreeView row::nth-child (even) {
background-color: #dddddd;
}
</programlisting>
</example>
</listitem>
<listitem>
<para>
If your container renders child widgets within different regions,
make it implement #GtkContainer get_path_for_child(<!-- -->). This function
lets containers assign a special #GtkWidgetPath to child widgets
depending on their role/region. This is necessary to extend the
concept above throughout the widget hierarchy.
</para>
<para>
For example, a #GtkNotebook modifies the tab labels' #GtkWidgetPath
so the "tab" region is added. This makes it possible to theme tab
labels through:
</para>
<example>
<title>Theming a widget within a parent container region</title>
<programlisting>
GtkNotebook tab GtkLabel {
font: Sans 8;
}
</programlisting>
</example>
</listitem>
<listitem>
If you intend several visual elements to look interconnected,
make sure you specify rendered elements' connection areas with
gtk_style_context_set_junction_sides(). It is of course up to the
theme to make use of this information or not.
</listitem>
<listitem>
<para>
#GtkStyleContext supports implicit animations on state changes for
the most simple case out-of-the-box: widgets with a single animatable
area, whose state is changed with gtk_widget_set_state_flags() or
gtk_widget_unset_state_flags(). These functions trigger animated
transitions for the affected state flags. Examples of widgets for
which this kind of animation may be sufficient are #GtkButton or
#GtkEntry.
</para>
<para>
If your widget consists of more than a simple area, and these areas
may be rendered with different states, make sure to mark the rendered
areas with gtk_style_context_push_animatable_region() and
gtk_style_context_pop_animatable_region().
</para>
<para>
gtk_style_context_notify_state_change() may be used to trigger a
transition for a given state. The region ID will determine the
animatable region that is affected by this transition.
</para>
</listitem>
</orderedlist>
</section>
</chapter>