Up: 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.
- install. The user associates the most recently selected
Tv tool from a subtool selection menu to a logical display
- clone. Multiple copies of the same Tv can be installed
on different Tv Tool's. These copies are not accessable from the
main application program and can be therefore used to store graphical results
for visual comparison.
- init. An aplication can supply an initialisation function
which selects a default geometry for display (eg; an image can be scaled
to fit the display screen). Using this button will return the displayed
data to the standard projection after zooming or rotating.
When the screen is exposed or resized repaint routines are called to
refresh the display appropriately. Users can invoke a repaint directly
by pressing this button.
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.
Up: Tv Tool