B. Programming with Agentk

  Agentk (pronounced agent-t-k) is extension to the Tcl/Tk toolkit that facilitate the incorporation of various graphical and motion-based effects into user interfaces. It requires Tcl/Tk 8.3 (or a later version) and requires Jeff Hobbs' megawidget creation package (included in the distribution) to operate. Agentk is available on the Web from the Agentk Web site:

http://www.cc.gatech.edu/ mccricks/agentk/

The remainder of this appendix describes the widgets, options, subcommands, and bindings for Agentk as well as several sample programs that are included with the distribution.

B.1 Agentk widgets

The fade widget fades in and out between several blocks of text and graphics. The gradual change will be less distracting than a sudden switch, yet will allow multiple information blocks to be displayed in a single area. The programmer controls the speed with which the fade occurs depending on the nature of the application: if the widget is used in a non-agent application interface, a quick fade might be used, while an agent might call for a slower, less intrusive fade.

The ticker widget provides a ticker tape display that scrolls or "tickers" information across the screen. As with the fade widget, a slow tickering can be less distracting than a sudden switch in information. The ticker widget is better suited for streams of text with arbitrary length - news headlines, weather reports, traffic updates. The programmer can control the rate of the tickering depending on the nature of the programming. The user can grab the ticker using the mouse to stop the tickering effect to make it easier to see the information. By dragging the information at a certain velocity, the user can change the speed and direction of the tickering effect.

Roll widgets are similar to ticker widgets, except they scroll information vertically. They work best for lists of information like golf leaderboards or top sales charts.

The navigation bar communicates information about the contents of a list by using the space in the trough of the scrollbar to represent the list entry. Each list entry is represented with a graphical line. Properties of the list entries are reflected in properties of the graphical lines.

B.2 Options, subcommands, and bindings

This section describes the subcommands, options, and bindings for the Agentk animated widgets.

A subcommand is a command that is available within a widget command. For example, all Tcl/Tk widgets (including the animated widgets) support the configure subcommand for querying and altering the widget options. Animated widgets additionally support the following subcommands:

• run command starts the animation effect for the widget.
• pause command pauses the animation until the run command is reissued.
• jump (fade only) jumps to the next item in the fade display list.

A configuration option alters the behavior and appearance of a widget. Common options include -geometry, -font, and -width. The following are some selected options that are available with the animated widgets.

• -speed indicates the speed with which the animation runs.
• -delay (fade only) is the delay in milliseconds before an item that has faded in begins to fade out.
• -text[variable], -bitmap[variable], and -image[variable] control the information that appears in the widget. When the value is changed, the new information animates into view as the old information disappears. For the variable options (such as -textvariable), the contents of each variable are animated on the screen. Only one of these options can be used for any given widget (the variable options have highest precedence, and images take precedence over bitmaps, and bitmaps over text).
• -separator contains a sequence of characters that separate entries in the ticker and roll widgets. This option is overridden by the -separatorbitmap and -separatorimage options, which can contain a bitmap or image separator.
• -markupstyle indicates a typeface markup (either bold, italic, or a color) used to highlight changes in information. Thus, if new text appears and the markupstyle is set to red, the new text will be red. To end the highlighting, -markupcount can be set to a number of iterations or -markuptimeout can be set to a length of time after which the markups will disappear. Section 6.4.1 talks more about automatic markups.
• -shadowhistory (a boolean) indicates whether history-based shadowing should be enabled. If it is, previous states of the displayed information (text only) are shown using a shadow effect. See Figure 19 for an example. -shadowcount and -shadowtimeout can be used to remove the shadowing after some number of iterations or some length of time. Section 6.4.2 talks more about history-based shadowing.
• -throw (a boolean) indicates whether speed should be adjusted when the user ``throws'' a ticker or roll widget; that is, drags and releases it.
• -drive synchronizes widgets of the same type so that they will run in lock step. For example, the two fade widgets in Figure 21 must always run together as one widget shows images and the other shows labels for the images. As one drives the other, each step in the two fades will be calculated and displayed at the same time.

 

 

Figure 21: The fade interface of the CWIC passive Web browser. The display consists of two fade widgets running in sync using the -drive option. The upper one fades between images and the lower one fades between text labels for the image. The first frame shows an initial image and text. The next two frames show how the image and text fade away as the new ones fade in. The final two frames show how the new image and text appear in their entirety as the old disappear.

Bindings define the behavior when certain actions are performed by a user on a widget. Below are the default bindings. A programmer can tailor the bindings based on the needs of their applications.

• ButtonPress binding stops the animation effect. Users who want to read the text without being distracted by the animation can press and hold the mouse button.
• Motion of the mouse while the mouse button is being held down drags the ticker and roll widgets.
• ButtonRelease for the fade widget jumps to the next block of information. For the ticker and roll widget, it calculates a new speed based on the speed at which the widget was dragged. For all widgets it restarts the animation effect.

B.3 Demos

Agentk comes with several demo scripts that showcase its power. Most of them simply demonstrate the abilities of the widget, though some provide useful information monitoring capabilities. The Agentk demo programs are:

• NewsAgent: (Unix only) A simple news agent that monitors the Yahoo news site and constantly tickers the news headers across the screen. When new news arrives, a message rapidly fades in and out until a button is pressed. The button pulls up a simple news reader. Written by Emily Stretch.
• checklpq: (Unix only) Printer queue checker using a roll widget.
• demo-fade: Fade widgets that show images and captions in sync.
• demo-navbar: Navigation bar widget that highlights names in a list.
• demo-roll: Displays the script itself in a roll widget.
• demo-ticker: Displays the script itself in a ticker widget.
• tkwatch: (Unix only) Displays stock quotes, sports scores, news headlines, and more using either a fade, ticker, or list widget. This is the system used in the observational study described in Chapter 7.