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Chapter 10. The Scale Widget

A Scale widget looks similar to a Scrollbar but doesn't scroll anything other than itself. What it does is keep track of a number. When you change the position of the button in the Scale, the numeric value associated with the Scale changes. Some things you can do with a Scale widget are:

  • Create a widget from which a user can select a number between 1 and 100.

  • Create three Scales, each representing a value in an RGB (red, green, blue) number.

  • Create four sliders, each representing a portion of an IP address. Each Scale can go from 0 to 255, and it would probably be smart to start them at 255. Use a Label widget to show the completed IP address, periods and all.

  • Create a temperature Scale that starts at -50 and goes to 130 degrees.

  • Show the amount of rainfall so far this year. The Scale can be marked to show every five inches.

The Scale widget can be placed horizontally or vertically, depending on where you have the most room in your application window. Figure 10-1 shows a scale widget.

Figure 10-1

Figure 10-1. Scale widget

10.1. Creating a Scale

As with other widgets, to create a Scale, use a parent widget and pass options to the Scale to change its configuration:

$parent->Scale( [ option => value ] )->pack;

Use one of the geometry managers discussed in Chapter 2, "Geometry Management" to place it on the screen (such as pack, as shown in the preceding code).

Most of the options associated with the Scale widget are standard options used with all other widgets. All the possible options are in the following list. A discussion of special options that have slightly different meanings for the Scale and options that are specific to the Scale widget follows the list.

-activebackground => color
Sets the color the slider's background should be when the cursor is over the slider (-state is 'active').

-background => color
Sets the color the slider's background should be when the cursor is not over the slider (-state is 'normal').

-bigincrement => amount
Sets the amount by which the slider will change value when required to do so in large increments. Default is 0, causing the value to change by 1/10 the top value of the Scale. -bigincrement is used only when Control-Up/Down/Left/Right is pressed.

-borderwidth => amount
Sets the width of the edges of the widget. Default is 2.

-command => callback
Sets the callback invoked when the slider is moved.

-cursor => cursorname
Determines the cursor to display when the mouse is over the Scale.

-digits => amount
Indicates how many significant digits to retain when conversion from a number to a string takes place.

-font => fontname
Sets the font used to display any text in the Scale.

-foreground => color
Sets the color of the text displayed in the Scale.

-from => value
Indicates the low end of the Scale values. Default is 0.

-highlightbackground => color
Sets the color of the highlight rectangle displayed around the Scale when it does not have the keyboard focus.

-highlightcolor => color
Sets the color of the highlight rectangle displayed around the Scale when it has the keyboard focus.

-highlightthickness => amount
Sets the thickness of the highlight rectangle displayed around the Scale.

-label => labelstring
Describes a label for the Scale. Default is no label.

-length => amount
Sets the length of the slider (the long direction, regardless of the value of -orient) in a valid screen distance.

-orient => 'vertical' | 'horizontal'
Sets the direction the Scale is drawn.

-relief => 'raised'|'sunken'|'flat'|'ridge'|'groove'|'solid'
Determines how the edges of the widget are drawn.

-repeatdelay => milliseconds
Sets the number of milliseconds the widget waits before repeating.

-repeatinterval => milliseconds
Sets the number of milliseconds the widget delays between repeats.

-resolution => value
Sets the increments by which the value in the Scale will change. Default is 1.

-showvalue => 0 | 1
If set to 0, the value of the slider setting is not shown at all.

-sliderlength => value
Sets the size of the slider (inside the widget). Default is 25.

-state => 'normal' | 'active' | 'disabled'
Determines the state of the widget and whether or not the user can interact with it.

-takefocus => 1 | 0 | undef
Determines whether or not the widget can receive keyboard focus. Default is to let the program decide.

-tickinterval => value
Describes the labels drawn by the right (or on the bottom) of the Scale. Labels are drawn for every value except 0 (which means no labels will be drawn at all). Default is 0.

-to => value
Sets the top value of the Scale. Default is 100.

-troughcolor=> color
Sets the color of the area behind the slider button (same as a Scrollbar).

-variable => \$variable
Sets the variable in which the slider value is stored.

-width => amount
Sets the width of the skinny part of the slider (regardless of the value associated with -orient).



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