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



____________________________________________________________________________________________________________

NAME
       ttk::intro - Introduction to the Tk theme engine
____________________________________________________________________________________________________________

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 appear-ance. appearance.
       ance.  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 con-tains contains
       tains uparrow, downarrow, trough and slider elements.

       Element names use a recursive dotted notation.  For example, uparrow identifies a generic arrow  ele-ment, element,
       ment, 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  exam-ple, example,
       ple,  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(n) 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  But-tonRelease ButtonRelease
       tonRelease  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(n), ttk::style(n)



Tk                                                   8.5                                       ttk::intro(n)