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'\"
'\" Copyright (c) 2004 Joe English
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
'\" RCS: @(#) $Id: ttk_intro.n,v 1.4 2007/10/22 14:33:13 dkf Exp $
'\"
.so man.macros
.TH ttk_intro n 8.5 Tk "Tk Themed Widget"
.BS
.SH NAME
ttk_intro \- Introduction to the Tk theme engine
.BE
.SH "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 widgets appearance is
.SH "THEMES"
A \fItheme\fR is a collection of elements and styles that determine the look
and feel of the widget set. Themes can be used to:
.IP \(bu
Isolate platform differences (X11 vs. classic Windows vs. XP vs. Aqua ...)
.IP \(bu
Adapt to display limitations (low-color, grayscale, monochrome, tiny screens)
.IP \(bu
Accessibility (high contrast, large type)
.IP \(bu
Application suite "branding"
.IP \(bu
Blend in with the rest of the desktop (Gnome, KDE, Java)
.IP \(bu
And, of course: eye candy.
.SH "ELEMENTS"
An \fIelement\fR displays an individual part of a widget. For example, a
vertical scrollbar widget contains \fBuparrow\fR, \fBdownarrow\fR,
\fBtrough\fR and \fBslider\fR elements.
.PP
Element names use a recursive dotted notation. For example, \fBuparrow\fR
identifies a generic arrow element, and \fBScrollbar.arrow\fR and
\fBCombobox.uparrow\fR 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.
.PP
Like widgets, elements have \fIoptions\fR which specify what to display and
how to display it. For example, the \fBtext\fR element (which displays a text
string) has \fB\-text\fR, \fB\-font\fR, \fB\-foreground\fR,
\fB\-background\fR, \fB\-underline\fR, and \fB\-width\fR options. The value of
an element resource is taken from:
.IP \(bu
A dynamic setting specified by \fBstyle map\fR and the current state;
.IP \(bu
An option of the same name and type in the widget containing the element;
.IP \(bu
The default setting specified by \fBstyle default\fR; or
.IP \(bu
The element's built-in default value for the resource.
.SH "LAYOUTS"
A \fIlayout\fR specifies which elements make up a widget and how they are
arranged. The layout engine uses a simplified version of the \fBpack\fR
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 \fB\-side\fR option, and placed within the parcel according to the
\fB\-sticky\fR option. For example, the layout for a horizontal scrollbar:
.CS
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
}
}
.CE
By default, the layout for a widget is the same as its class name. Some
widgets may override this (for example, the \fBscrollbar\fR widget chooses
different layouts based on the \fB-orient\fR option).
.SH "STATES"
In standard Tk, many widgets have a \fB\-state\fR option which (in most cases)
is either \fBnormal\fR or \fBdisabled\fR. Some widgets support additional
states, such as the \fBentry\fR widget which has a \fBreadonly\fR state and
the various flavors of buttons which have \fBactive\fR state.
.PP
The themed Tk widgets generalizes this idea: every widget has a bitmap of
independent state flags. Widget state flags include \fBactive\fR,
\fBdisabled\fR, \fBpressed\fR, \fBfocus\fR, etc., (see \fIttk_widget(n)\fR for
the full list of state flags).
.PP
Instead of a \fB\-state\fR option, every widget now has a \fBstate\fR widget
command which is used to set or query the state. A \fIstate specification\fR
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.
.PP
For example, the class bindings for the \fBttk::button\fR widget are:
.CS
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> \e
{ %W instate {pressed} { %W state !pressed ; %W invoke } }
.CE
This specifies that the widget becomes \fBactive\fR when the pointer enters
the widget, and inactive when it leaves. Similarly it becomes \fBpressed\fR
when the mouse button is pressed, and \fB!pressed\fR 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 \fB\-command\fR is
invoked, but only if the button is currently in the \fBpressed\fR state. (The
actual bindings are a little more complicated than the above, but not by
much).
.PP
\fINote to self: rewrite that paragraph. It's horrible.\fR
.SH "STYLES"
Each widget is associated with a \fIstyle\fR, which specifies values for
element resources. 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:
.CS
style default TButton \e
-background #d9d9d9 \e
-foreground black \e
-relief raised \e
;
.CE
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 \fBstyle
map\fR command specifies dynamic resources for a particular style:
.CS
style map TButton \e
-background [list disabled #d9d9d9 active #ececec] \e
-foreground [list disabled #a3a3a3] \e
-relief [list {pressed !disabled} sunken] \e
;
.CE
.SH "SEE ALSO"
ttk_widget(n), ttk_style(n)
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