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The Logical Tv and the Tv Tool

The programmer works with a logical display device called a Tv. Tools that require graphical display devices can either reuse existing display devices (via calls to the appropriate pointer access functions) or must provide their own Tv device. During program execution a Tv is created using the New Tv Tool button of the main tool. Within reason any number of Tv's can be created. Tv's support the following button proceses. Tv's support both transient and retained graphical facilities. Transient graphics are lost following zooming or other repaint facilities, while retained graphics are not. Generally, transient graphics will not be displayed on cloned Tv's.

Interaction with the tool takes place through the mouse (assumed to have three buttons). The mouse generates 9 different event types from the combinations of these buttons with up, down and drag.


next up previous contents
Next: Interaction Up: Tv Tool Previous: Introduction   Contents
root 2017-09-19