Panel Items

A panel item consists of a string label and an associated variable of a certain type. The value of this variable is visualized by the appearance in the window, e.g., the position of a slider, and can be manipulated through the item, e.g., by dragging the slider.

Panel buttons are special panel items.

Remark: Panel items have to be created before the window is displayed for the first time.

Item Types

LEDA provides the following item types: Simple Items, Choice Items, Multiple Choice Items, Slider Items, Boolean Items

On the right you see a screenshot of the example of panel item types .

Example for Panel Item Types

Associating a Function with a Panel Item

It is possible to associate a function of type

  void (*action) (T x)

with a panel item where T is the type of the item. The action function is called after each item manipulation, e.g., dragging a slider or pressing a button, with the new value of the item as its argument.

The example for color shows how action functions can be associated with slider items to define the background color of a window.

Example Color Definition Panel

Remark: The value of the variable is only changed after the return of the action function. In this way, both the old and the new value of the variable are available in the action function.

The values of item variables may also be changed in the program. This has no effect on the display until the panel is actively redrawn for the next time.

The redraw_panel() operation redraws the panel area. The Example Progress Indicator uses a slider item to visualize the increasing value of a counter.

Example Progress Indicator