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# 1. Introduction

The Forms Library is a library of C-routines that allows you to build up interaction forms with buttons, sliders, input fields, dials, etc. in a very simple way. Following the X tradition, Forms Library does not enforce the look and feel of objects although in its default state, it does provide a consistent look and feel for all objects.

The Forms Library only uses the services provided by Xlib and should be compilable on all machines that have X installed and have an ANSI compatible compiler. Being based on Xlib,Forms Library is small and efficient. It can be used in both C and C++ programs and soon it will be available for other languages(1).

The basic procedure of using the Forms Library is as follows. First one or more forms are defined, by indicating what objects should be placed on them and where. Types of objects that can be placed on the forms include: boxes, texts, sliders, buttons, dials, input fields and many more. Even a clock can be placed on a form with one command. After the form has been defined it is displayed on the screen and control is given to a library call `fl_do_forms()`. This routine takes care of the interaction between the user and the form and returns as soon as some change occurs in the status of the form due to some user action. In this case control is returned to the program (indicating that the object changed) and the program can take action accordingly, after which control is returned again to the `fl_do_forms()` routine. Multiple forms can be handled simultaneously by the library and can be combined with windows of the application program. More advanced event handling via object callbacks is also supported.

The Forms Library is simple to use. Defining a form takes a few lines of code and interaction is fully handled by the library routines. A number of demo programs are provided to show how to piece together various parts of the library and demonstrate how easy forms are built and used. They can be found in the directory `demos`. Studying these demos is a good way of learning the system.

If you only have very simple applications for the Forms Library, e.g., to ask the user for a file name, or ask him a question or give him a short message, Goodies contains some even more simple routines for this. So, e.g., a form with the question "Do you want to quit?" can be made with one line of code.

To make designing forms even easier a Form Designer is provided. As its name implies, this is a program that lets you interactively design forms and generate the corresponding C-code. See section Introduction, and the following chapters for its use.

The current version of the software is already quite extended but we are working on further improvements. In particular, we plan on designing new classes of objects that can be placed on the forms. Adding classes to the system is not very complicated. Part IV of this document describes in detail how to do this yourself.

The following chapters will describe the basic application programmer's interface to the Forms Library and lead you through the different aspects of designing and using forms. In Getting Started we give some small and easy examples of the design and use of forms. In Defining Forms we describe how to define forms. This chapter just contains the basic classes of objects that can be placed on forms. Also, for some classes only the basic types are described and not all. For an overview of all classes and types of objects see Part III of this document. Doing Interaction describes how to set up interaction with forms. A very specific class of objects are free objects and canvases. The application program has full control over their appearance and interaction. They can be used to place anything on forms that is not supported by the standard objects. Free Objects describes their use. Finally, Goodies describes some built-in routines for simple interaction like asking questions and prompting for choices etc.

### Footnotes

### (1)

As of this writing, perl, Ada95, scheme, pascal, Fortran and python bindings are in beta testing.

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