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ttk::intro(n)                  Tk Themed Widget                  ttk::intro(n)


       ttk::intro - Introduction to the Tk theme engine

       The Tk themed widget set is based on a revised and enhanced version of TIP #48 ( specified
       style engine.  The main concepts are described below.  The basic idea is to separate, to the  extent  possible,
       the code implementing a widget's behavior from the code implementing its appearance.  Widget class bindings are
       primarily responsible for maintaining the widget state and invoking  callbacks;  all  aspects  of  the  widgets
       appearance is

       A  theme is a collection of elements and styles that determine the look and feel of the widget set.  Themes can
       be used to:

       ?      Isolate platform differences (X11 vs. classic Windows vs. XP vs. Aqua ...)

       ?      Adapt to display limitations (low-color, grayscale, monochrome, tiny screens)

       ?      Accessibility (high contrast, large type)

       ?      Application suite branding

       ?      Blend in with the rest of the desktop (Gnome, KDE, Java)

       ?      And, of course: eye candy.

       An element displays an individual part of a widget.  For example, a vertical scrollbar widget contains uparrow,
       downarrow, trough and slider elements.

       Element  names  use  a recursive dotted notation.  For example, uparrow identifies a generic arrow element, and
       Scrollbar.uparrow and Combobox.uparrow identify widget-specific elements.  When looking  for  an  element,  the
       style  engine  looks  for  the  specific  name  first, and if an element of that name is not found it looks for
       generic elements by stripping off successive leading components of the element name.

       Like widgets, elements have options which specify what to display and how to display it.  For example, the text
       element  (which  displays  a  text  string)  has -text, -font, -foreground, -background, -underline, and -width
       options.  The value of an element option is taken from:

       ?      An option of the same name and type in the widget containing the element;

       ?      A dynamic setting specified by style map and the current state;

       ?      The default setting specified by style configure; or

       ?      The element's built-in default value for the option.

       A layout specifies which elements make up a widget and how they are arranged.  The layout engine uses a simpli-
       fied  version  of the pack algorithm: starting with an initial cavity equal to the size of the widget, elements
       are allocated a parcel within the cavity along the side specified by the -side option, and  placed  within  the
       parcel according to the -sticky option.  For example, the layout for a horizontal scrollbar
              ttk::style layout Horizontal.TScrollbar {
                  Scrollbar.trough -children {
                Scrollbar.leftarrow -side left -sticky w
                Scrollbar.rightarrow -side right -sticky e
                Scrollbar.thumb -side left -expand true -sticky ew
       By  default,  the layout for a widget is the same as its class name.  Some widgets may override this (for exam-
       ple, the ttk::scrollbar widget chooses different layouts based on the -orient option).

       In standard Tk, many widgets have a -state option which (in most cases) is either  normal  or  disabled.   Some
       widgets  support additional states, such as the entry widget which has a readonly state and the various flavors
       of buttons which have active state.

       The themed Tk widgets generalizes this idea: every widget has a bitmap  of  independent  state  flags.   Widget
       state  flags  include  active,  disabled,  pressed, focus, etc., (see ttk::widget(n) for the full list of state

       Instead of a -state option, every widget now has a state widget command which is  used  to  set  or  query  the
       state.   A state specification is a list of symbolic state names indicating which bits are set, each optionally
       prefixed with an exclamation point indicating that the bit is cleared instead.

       For example, the class bindings for the ttk::button widget are:
              bind TButton <Enter>{ %W state active }
              bind TButton <Leave>{ %W state !active }
              bind TButton <ButtonPress-1>{ %W state pressed }
              bind TButton <Button1-Leave>{ %W state !pressed }
              bind TButton <Button1-Enter>{ %W state pressed }
              bind TButton <ButtonRelease-1>\
                  { %W instate {pressed} { %W state !pressed ; %W invoke } }
       This specifies that the widget becomes active when the pointer enters the widget, and inactive when it  leaves.
       Similarly  it  becomes  pressed  when the mouse button is pressed, and !pressed on the ButtonRelease event.  In
       addition, the button unpresses if pointer is dragged outside the  widget  while  Button-1  is  held  down,  and
       represses  if  it's  dragged  back  in.   Finally,  when the mouse button is released, the widget's -command is
       invoked, but only if the button is currently in the pressed state.  (The actual bindings are a little more com-
       plicated than the above, but not by much).

       Note to self: rewrite that paragraph.  It's horrible.

       Each  widget  is associated with a style, which specifies values for element options.  Style names use a recur-
       sive dotted notation like layouts and elements; by default, widgets use the class name to look up  a  style  in
       the current theme.  For example:
              ttk::style configure TButton \
                -background #d9d9d9 \
                -foreground black \
                -relief raised \
       Many  elements  are displayed differently depending on the widget state.  For example, buttons have a different
       background when they are active, a different foreground when disabled, and a  different  relief  when  pressed.
       The style map command specifies dynamic option settings for a particular style:
              ttk::style map TButton \
                -background [list disabled #d9d9d9  active #ececec] \
                -foreground [list disabled #a3a3a3] \
                -relief [list {pressed !disabled} sunken] \

       ttk::widget(n), ttk::style(n)

Tk                                    8.5                        ttk::intro(n)