# General Information on Using Libsx

Using libsx is pretty simple. At the minimum, you #include "libsx.h" and link with libsx.a. To actually have X windows pop open and such, you need to do the following:

1. To get everything started, you should call OpenDisplay() ). If OpenDisplay() ) returns a non-zero value, it's ok to go on. OpenDisplay() ) creates what will eventually be your first window.
2. After calling OpenDisplay() ), you can go on to create all sorts of widgets with the MakeXXX() calls. You can lay them out with calls to SetWidgetPos() .
3. When you are done creating the user interface, call ShowDisplay() . This causes the window and components you've created to be displayed on the workstation screen.

   Until you call ShowDisplay() , the user can NOT see your window, and drawing into drawing areas has NO effect.

4. If you need to, you can call any of the color allocation functions such as GetStandardColors() , etc.
5. Finally, once the window is displayed and you've done all the initializations you wish, you must then call MainLoop() . After you call MainLoop() , events get processed as they come in and your callback functions are called as necessary.

   After calling MainLoop() , the correct way for your program to exit is to have one of your callback routines call exit() when appropriate (like after the user clicks on a "Quit" button).

6. There is a predefined procedure CloseProcedure() , with a single argument

                CloseProcedure(Widget w)

   which is called each time the user presses the "Delete Window" slot of the window bar. Its default action is to close the active window, and to exit the application if that window is the original main window. You can redefine it to do whatever you like before closing (or to prevent the window being closed).

That's all you need to do. Even though that may look like a lot to do, it's really pretty simple in practice. For example, here is a hello world program with libsx:

    #include "libsx.h"

    main()
    {
      MakeLabel("Hello World!");
      MainLoop();
    }

Granted it's one more line than a standard printf() type of hello world program, but it's not all that bad.

Hello world programs are nice, but you don't tend to write very many of them. Real applications need to be able to do much more. Even these "real" programs aren't all that bad in libsx.

Here is a simple program that opens a window with a quit button and a drawing area that you could use to draw whatever graphics you wanted:

    #include <stdio.h>
    #include "libsx.h"

    void quit(Widget w, void *data)
    {
      exit(0);
    }

    void draw_stuff(Widget w, int width, int height, void *data)
    {
      ClearDrawArea();
      DrawLine(0,0, width, height);   /* just draw a diagonal line */
    }

    int main(int argc, char **argv)
    {
      Widget w[2];

      argc = OpenDisplay(argc, argv);
      if (argc == 0)                   /* woops, couldn't get started */
        exit(5);

      w[0] = MakeButton("Quit", quit, NULL);
      w[1] = MakeDrawArea(300,300, draw_stuff, NULL);

      SetWidgetPos(w[1], PLACE_UNDER, w[0], NO_CARE, NULL);

      ShowDisplay();
      GetStandardColors();

      MainLoop();   /* off we go! */
    }

Here is how one would redefine the CloseProcedure to make it do some further stuff before closing.

    void CloseProcedure(Widget w)
    {
      if(w == GetTopWidget(a_widget_in_the_main_window)))
        {
        printf("Main window closed by user\n");
        exit(0);
        }
      else
        {
        printf("Auxilliary window closed by user\n");
        SetCurrentWindow(w);
        CloseWindow(); /* This actually closes the window */
        }

      /* Don't include exit(0) or CloseWindow() if you want to prevent the
         window from closing */
    }

The code above is the basic skeleton for a libsx program, even complicated ones. First you open the display with OpenDisplay(). Then you build your interface by creating a bunch of widgets with the MakeXXX() calls. Next you layout the display by specifying the relative positions of the widgets to each other. Then you would get any fonts or colors you may need, and finally you just enter the main loop.

In libsx, your callback functions are where all the real work happens. The program above has two callback functions, quit() and draw_stuff(). They are tied to events that happen in the interface. When the user clicks on the "Quit" button, your quit() function is called. When the drawing area gets resized or needs to be redrawn, your draw_stuff() function gets called.

Usually the process of creating the interface would get separated into a separate function that is easy to modify (instead of cluttering up main). However, the basic outline is the same as above. The only real difference with more complicated interfaces is that they usually have a lot more calls to the MakeXXX() functions and they tend to make use of the extra void pointer argument in the callback routines.

If you'd like more examples, take a look at the provided source code. There are several reasonable examples of varying complexity that you can take and modify as you like. Each of the demos tries to demonstrate a certain group of features, so take a look at each to find the one that most closely matches what you want to do and start hacking from there!