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 con‐
cepts 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
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 Com‐
bobox.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 hori‐
zontal 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 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, dis‐
abled, 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 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).
Note to self: rewrite that paragraph. It's horrible.
STYLES
Each widget is associated with a style, which specifies values for ele‐
ment 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 ALSOttk::widget(n), ttk::style(n)Tk 8.5 ttk::intro(n)
