All the visible and audible elements of timelines are part of events. Each event is attached to one or more categories. In general, the boundaries of a category contain all the visible aspects of events which are attached to them. An exception to this rule is made for event labels.


A simple event

Events have a start time and an end time. In their simplest form, events are displayed as an open-ended box and have a text label. The author of a timeline can make the box and/or label invisible.

The color used for drawing an event is part of the event's definition. The definition also contains a label design that defines the colors and font information for drawing the event's label.

The display of an event can be augmented with an image.

An audio file or video file can be attached to an event. The audio or video will play when the QViewer's display time is between the start and end time of the event and the center of the window is within the region defined by the roll-off style parameters.

An event can be associated with multiple links. These links can be to other timeline files, to events in the same or different timeline files, and to Web pages or any other type of object that can be handled by a Web browser.

An event can be selected by clicking with the mouse on any part of the event's representation on the screen. Events are often partly transparent and the event selected is the one nearest the viewpoint at the point that is clicked.

After an event is selected, the user can see a list of all the links that have the event as their source. The user can also choose to see a page of information about the event and category on their Web browser. This information can include source citations and text notes attached to the event and category.

An event can request that its drawing be handled by an extension. Extensions are small pieces of computer code that allow drawing and other behavior to be extended or customized. Certain useful extensions are included with the QViewer. Authors can write other extensions and make them available to others. The QViewer limits the actions allowed to extensions to protect the user's machine and data.


Drawing in endcuts

Some events represent values that change continuously with time. An event extension can display a representation of that value in its endcut. The endcut is the rectangle where the category containing the event intersects the display time. An example of a continuous time function is generated by the moon phase extension. A picture of the moon's phase at the QViewer's display time is displayed in the endcut.

Whenever an event is attached to a category, it is given two number ranges that define when that event is shown. This is part of the mechanism for data hiding. One range is related to the current time scale. As the time scale changes the events are shown or hidden based on whether the time scale is within the given range. The other range is related to a choice in a pop-up menu attached to the event. Changing the menu choice will show or hide the event. To be visible the event must be shown by both range settings. The default settings for both ranges is 0-100 which causes the event to always be shown.


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