NAME

       ttk::intro - Introduction to the Tk theme engine
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OVERVIEW

       The  Tk  themed  widget  set is based on a revised and enhanced version of TIP #48 (http://tip.tcl.tk/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 widget's appearance are controlled by the style of the widget (i.e. the style of the
       elements of the widget).

THEMES

       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.

ELEMENTS

       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.

LAYOUTS

       A  layout  specifies which elements make up a widget and how they are arranged.  The layout engine uses a
       simplified 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 is:

              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
       example, the ttk::scrollbar widget chooses different layouts based on the -orient option).

STATES

       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(3tk) for the full
       list of state flags).

       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 complicated than the above, but not by much).

STYLES

       Each  widget  is  associated with a style, which specifies values for element options.  Style names use a
       recursive 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] \
                ;

SEE ALSO

       ttk::widget(3tk), ttk::style(3tk)