Fr Widget Basics

This chapter teaches you the basics of Fr_Widget toolkit

Writing your first Fr_Widget program
Basically, you need always to have a Fr_CoinWindow. This widget is the container of the other widgets you create. It is a subclass of Fr_Group. The Fr_CoinWindow used to distribute events and hold a link to each widget you have in your window.

Fr_CoinWindow doesn't draw any thing and it is not restricted to any dimensions. But there must be a such windows for getting your Fr_Widgets work. If FreeCAD adapt this toolkit someday, the Fr_CoinWindow should be always available and you shouldn't required to create one. But at the moment, you have to create one Fr_CoinWindow whenever you need to use the toolkit. Notice that you shouldn't make several of Fr_CoinWindow.. Only once.

The widgets interact with the user using the callback system.

Explaining the code

 * First line imports the fr_arrow_widget. Later we use it to create the widget itself.
 * Second line imports the fr_coinwindow. As mentioned this is the container of the system. Without this widget, you will not be able to show anything
 * Third line is math library from Python. It is required for now but this will change. It is used to convert the rotation angle to radians. But in the future the interface angles will be in degree. Internally is still radians as COIN3D is in radians.

Creating Fr_Line_widget as an example
Lets start creating a new drawing widget. This widget will draw a line and has a label. We need to get two vertices to draw the line. The widget itself is a subclass of the abstract object called Fr_Widget. Fr_Widget is the base class for all widgets. It contains basic variable, objects and functions definitions. Some of these are not implemented and you have to implemented. If you will use any function that aren't implemented, an exception will popup.

Part1:
The class declaration of our new object:

The line (super) must be written in the first line after the definition of the class since we want to initialize the abstract widget(Fr_Widget) before changing the internal objects and variables. We have as arguments to the widget:(vertices, label and line width). You must give exactly 2 vertices to the class, but line width and label is optional. Default line width is be 1.

There are four callbacks that we should define if we want to take benefit of the events. These are external function user should define them to do other tasks as events occur. For example mouse click or keyboard events ..etc.

The last two lines are related to Coin3d. The first one is a coin.SoSwitch object in coin which can be used to hide or show the drawn object. The other line is the configuration of that switch. We allow by default showing all objects.