Version 5.0 The LEDA User Manual

changes. The contents of the result scene is stored in a container of type R. The
input scene must be a Basic Scene with a container of type I. The update function
void (∗f update)(const I& input, R& result) gets the contents of this input scene
and computes the contents result of the result scene. We say that the result scene
depends on its input scene.
3. Basic Scenes (type GeoBaseScene)
Edit Scenes and Result Scenes are derived from Basic Scenes. The basic scene type
works on container types providing an interface as the list of the STL library. More
precisely, CONTAINER has to support the following type definitions and STL-like
operations:
• value type - the type T of the values the container holds
• iterator
• operations begin( ) and end( ) returning an iterator that can be used for
begining (ending) the traversal of the container
• void push back(const T &) for inserting an element at the end of the container
• iterator insert(iterator it, const T &) for inserting an element (before it)
• void erase(iterator it) for erasing an element at position it
• operation bool empty( ) returning true if the container is empty, false otherwise
That means, that LEDA lists can be used as well as containers.
The programming interface of GeoWin provides various operations to create Edit Scenes
and Result Scenes. Basic Scenes are not created directly by the operations of the programming
interface, but they are used for derivation of the other scene types, and we will
find them in the programming interface, when both Edit and Result Scenes are supported
by an operation.
GeoWin - class
We explain some important terms of the GeoWin data type. Every instance GW of
GeoWin can maintain a number of geo scenes.
Visible scenes will be displayed by GW , non-visible scenes will not be displayed. Displayed
means, that the contents of the scene will be displayed. A special case is the active scene
of GW . Every GeoWin can have at most one active scene. The active scene is an Edit
Scene with input focus. That means that this scene is currently edited by the user through
the interactive interface. Note that the currently active scene will be displayed.
Another important topic is the display order of scenes. Every scene has an associated
non-negative z-coordinate. When a scene is created, it gets z-coordinate 0. When GW
redraws a scene, the contents of this scene and the contents of its visible dependent scenes
is drawn. In the redraw-operation of GeoWin the scenes with higher z-coordinates will be
drawn in the background of scenes with lower z-coordinate.The scenes with z-coordinate