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21. GTK's rc Files

GTK has its own way of dealing with application defaults, by using rc files. These can be used to set the colors of just about any widget, and can also be used to tile pixmaps onto the background of some widgets.

21.1 Functions For rc Files

When your application starts, you should include a call to:

void gtk_rc_parse( char *filename );

Passing in the filename of your rc file. This will cause GTK to parse this file, and use the style settings for the widget types defined there.

If you wish to have a special set of widgets that can take on a different style from others, or any other logical division of widgets, use a call to:

void gtk_widget_set_name( GtkWidget *widget,
                          gchar     *name );

Passing your newly created widget as the first argument, and the name you wish to give it as the second. This will allow you to change the attributes of this widget by name through the rc file.

If we use a call something like this:

button = gtk_button_new_with_label ("Special Button");
gtk_widget_set_name (button, "special button");

Then this button is given the name "special button" and may be addressed by name in the rc file as "special button.GtkButton". [<--- Verify ME!]

The example rc file below, sets the properties of the main window, and lets all children of that main window inherit the style described by the "main button" style. The code used in the application is:

window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
gtk_widget_set_name (window, "main window");

And then the style is defined in the rc file using:

widget "main window.*GtkButton*" style "main_button"

Which sets all the Button widgets in the "main window" to the "main_buttons" style as defined in the rc file.

As you can see, this is a fairly powerful and flexible system. Use your imagination as to how best to take advantage of this.

21.2 GTK's rc File Format

The format of the GTK file is illustrated in the example below. This is the testgtkrc file from the GTK distribution, but I've added a few comments and things. You may wish to include this explanation in your application to allow the user to fine tune his application.

There are several directives to change the attributes of a widget.

In addition to this, there are several states a widget can be in, and you can set different colors, pixmaps and fonts for each state. These states are:

When using the "fg" and "bg" keywords to set the colors of widgets, the format is:

fg[<STATE>] = { Red, Green, Blue }

Where STATE is one of the above states (PRELIGHT, ACTIVE, etc), and the Red, Green and Blue are values in the range of 0 - 1.0, { 1.0, 1.0, 1.0 } being white. They must be in float form, or they will register as 0, so a straight "1" will not work, it must be "1.0". A straight "0" is fine because it doesn't matter if it's not recognized. Unrecognized values are set to 0.

bg_pixmap is very similar to the above, except the colors are replaced by a filename.

pixmap_path is a list of paths separated by ":"'s. These paths will be searched for any pixmap you specify.

The font directive is simply:

font = "<font name>"

The only hard part is figuring out the font string. Using xfontsel or a similar utility should help.

The "widget_class" sets the style of a class of widgets. These classes are listed in the widget overview on the class hierarchy.

The "widget" directive sets a specifically named set of widgets to a given style, overriding any style set for the given widget class. These widgets are registered inside the application using the gtk_widget_set_name() call. This allows you to specify the attributes of a widget on a per widget basis, rather than setting the attributes of an entire widget class. I urge you to document any of these special widgets so users may customize them.

When the keyword parent is used as an attribute, the widget will take on the attributes of its parent in the application.

When defining a style, you may assign the attributes of a previously defined style to this new one.

style "main_button" = "button"
  font = "-adobe-helvetica-medium-r-normal--*-100-*-*-*-*-*-*"
  bg[PRELIGHT] = { 0.75, 0, 0 }

This example takes the "button" style, and creates a new "main_button" style simply by changing the font and prelight background color of the "button" style.

Of course, many of these attributes don't apply to all widgets. It's a simple matter of common sense really. Anything that could apply, should.

21.3 Example rc file

# pixmap_path "<dir 1>:<dir 2>:<dir 3>:..."
pixmap_path "/usr/include/X11R6/pixmaps:/home/imain/pixmaps"
# style <name> [= <name>]
# {
#   <option>
# }
# widget <widget_set> style <style_name>
# widget_class <widget_class_set> style <style_name>

# Here is a list of all the possible states.  Note that some do not apply to
# certain widgets.
# NORMAL - The normal state of a widget, without the mouse over top of
# it, and not being pressed, etc.
# PRELIGHT - When the mouse is over top of the widget, colors defined
# using this state will be in effect.
# ACTIVE - When the widget is pressed or clicked it will be active, and
# the attributes assigned by this tag will be in effect.
# INSENSITIVE - When a widget is set insensitive, and cannot be
# activated, it will take these attributes.
# SELECTED - When an object is selected, it takes these attributes.
# Given these states, we can set the attributes of the widgets in each of
# these states using the following directives.
# fg - Sets the foreground color of a widget.
# fg - Sets the background color of a widget.
# bg_pixmap - Sets the background of a widget to a tiled pixmap.
# font - Sets the font to be used with the given widget.

# This sets a style called "button".  The name is not really important, as
# it is assigned to the actual widgets at the bottom of the file.

style "window"
  #This sets the padding around the window to the pixmap specified.
  #bg_pixmap[<STATE>] = "<pixmap filename>"
  bg_pixmap[NORMAL] = "warning.xpm"

style "scale"
  #Sets the foreground color (font color) to red when in the "NORMAL"
  fg[NORMAL] = { 1.0, 0, 0 }
  #Sets the background pixmap of this widget to that of its parent.
  bg_pixmap[NORMAL] = "<parent>"

style "button"
  # This shows all the possible states for a button.  The only one that
  # doesn't apply is the SELECTED state.
  fg[PRELIGHT] = { 0, 1.0, 1.0 }
  bg[PRELIGHT] = { 0, 0, 1.0 }
  bg[ACTIVE] = { 1.0, 0, 0 }
  fg[ACTIVE] = { 0, 1.0, 0 }
  bg[NORMAL] = { 1.0, 1.0, 0 }
  fg[NORMAL] = { .99, 0, .99 }
  bg[INSENSITIVE] = { 1.0, 1.0, 1.0 }
  fg[INSENSITIVE] = { 1.0, 0, 1.0 }

# In this example, we inherit the attributes of the "button" style and then
# override the font and background color when prelit to create a new
# "main_button" style.

style "main_button" = "button"
  font = "-adobe-helvetica-medium-r-normal--*-100-*-*-*-*-*-*"
  bg[PRELIGHT] = { 0.75, 0, 0 }

style "toggle_button" = "button"
  fg[NORMAL] = { 1.0, 0, 0 }
  fg[ACTIVE] = { 1.0, 0, 0 }
  # This sets the background pixmap of the toggle_button to that of its
  # parent widget (as defined in the application).
  bg_pixmap[NORMAL] = "<parent>"

style "text"
  bg_pixmap[NORMAL] = "marble.xpm"
  fg[NORMAL] = { 1.0, 1.0, 1.0 }

style "ruler"
  font = "-adobe-helvetica-medium-r-normal--*-80-*-*-*-*-*-*"

# pixmap_path "~/.pixmaps"

# These set the widget types to use the styles defined above.
# The widget types are listed in the class hierarchy, but could probably be
# just listed in this document for the users reference.

widget_class "GtkWindow" style "window"
widget_class "GtkDialog" style "window"
widget_class "GtkFileSelection" style "window"
widget_class "*Gtk*Scale" style "scale"
widget_class "*GtkCheckButton*" style "toggle_button"
widget_class "*GtkRadioButton*" style "toggle_button"
widget_class "*GtkButton*" style "button"
widget_class "*Ruler" style "ruler"
widget_class "*GtkText" style "text"

# This sets all the buttons that are children of the "main window" to
# the main_button style.  These must be documented to be taken advantage of.
widget "main window.*GtkButton*" style "main_button"

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