ttk::intro - phpMan

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

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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 ele-
ments 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:

o isolate platform differences (X11 vs. classic Windows vs. XP vs. Aqua ...)

o adapt to display limitations (low-color, grayscale, monochrome, tiny screens)

o accessibility (high contrast, large type)

o application suite branding

o blend in with the rest of the desktop (Gnome, KDE, Java)

o 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 ele-
ments. 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, -fore-
ground, -background, -underline, and -width options. The value of an element option is
taken from:

o an option of the same name and type in the widget containing the element;

o a dynamic setting specified by style map and the current state;

o the default setting specified by style configure; or

o 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 over-
ride 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 indicat-
ing 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, but-
tons have a different background when they are active, a different foreground when dis-
abled, 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] \
;