Lab 12: Radio buttons

A set of radio button widgets allows the user to choose only one of the predefined set of options. In FLTK the radio button is implemented by Fl_Round_Button class.
To ensure mutually exclusive operation (only one button is selected at a time), the radio buttons must be arranged in groups (FLTK class Fl_Group). It's possible that initially none of the radio buttons in a group are selected.
In this lab we implement a set of radio buttons and use a new CRadioSelector class to detect user choice when the callback function handles the user interaction with the widget.

The prototype for this project is Lab 4, an empty window:
```
    c255labs\labs\c255_lab04
```
Make a copy of Lab 4 subfolder, or download and unzip c255_lab04.zip
Rename the new folder as c255_lab12_radio_btn.
Open solution file in Visual Studio and finish the usual steps to rename the project.

Start FLUID program and open project


    c255labs\labs\c255_lab12_radio_btn\fluid_project\CFluidWindow.fl

Select Window win_app object in FLUID tree view. Use menu
```
    New/Buttons/Round button
```
Change properties/C++ class type from Normal to Radio.
Add two more radio buttons (tip: once you add one radio button, you can then copy and paste the rest.)

Name the widgets in Properties/C++


    rdo_line
    rdo_circle
    rdo_rectangle

Create a group:
1. Select all three radio buttons in the project tree view by using shift/down-arrow keys.
2. Hit F7.
Save FLUID project and generate C++ code by
```
    File/Write Code...
```

Open solution


    c255labs\labs\c255_lab12_radio_btn\c255_lab12.sln

in Visual Studio.

Download the new versions of
- CMainWindow.h
- CMainWindow.cpp
Compile and test the program.
Open CMainWindow.h in the text editor and examine the code:
- It is using a set of enumerated constants to uniquely identify each radio button.
- The click_radio_button() member function implements the user selection.
- The static callback_radio_button() is the callback function. This function is attached to each radio button on the screen.
- The CRadioSelector class remembers
  - button id, which is one of the enumerated constants
  - The pointer to the window class CMainWindow *
  Both of the data are needed when the callback is called for one of the radio buttons.
Open CMainWindow.cpp in the text editor. Examine the code. Notice that CMainWindow::show() attaches the same callback to each radio button object.
Using Visual Studio debugger, trace calls resulting from a mouse click that selects a radio button. What is the sequence of the invoked functions?
- Hint: specify a breakpoint in CMainWindow::callback_radio_button() and use the debugger to step into the calls.

This is a self-learning lab. There are no files to submit. Make sure to complete all required steps to build and test the project on your own home computer.