1. Introduction

1.1 What is a drag and drop protocol ?

I'm supposing you understand what ``drag and drop'' means. It's an intuitive way to exchange data between programs. A drag and drop protocol is the mean used by the programs to comunicate with each other in order to perform this data exchange. If the programs want to exchange information, they must be able to comunicate with each other in a common language. This language is the ``protocol''. Therefore, if you create your own protocol, chances are other programs will not understand you. So you must ``talk'' to other programs in a common language. In this way, when you receive a drop, you will receive a ``I dropped on you'' message, and you will understand the message no matter who send it to you. This is the purpose of a drag and drop protocol: to provide a common language for this kind of actions.

1.2 What is DND, and why should I use it ?

DND is a drag and drop protocol developed by César Crusius . A C interface to Xt-based programs is avaliable together with OffiX, a collection of useful utilities using the DND protocol.

If you have a program that could benefit from having drag and drop capabilities, DND might be a good choice for the following reasons:

It is public, unlike other ``standard'' protocols such as those used by Open Look and Motif. These two are incompatible, and aren't, as far as I know, published. Since Open Look and Motif applications are Xt based, you can choose to use DND or the specific protocol. This could be a compile-time option, for example.
You can use this protocol with any X program. Motif, Open Look and Athena applications can exchange data using the DND protocol. Non-Xt programs can incorporate DND protocol too (see section The DND internals ).
A C Xt interface is provided, so you can add drag and drop capabilities to an existing Xt program with a minimum effort.

Of course, there are also reasons to not use DND:

You must exchange data between your application and another that uses another protocol.
You don't need drag and drop, and in this case I wonder why are you still reading this.

I encourage you to use DND at least as a compile-time option for your program. There is already a good reason to do that: the ``files'' program furnished with OffiX. Won't it be good to be able to exchange data with a file manager? Certainly will! And, as you will note, it's very easy to bring this new capability to your program.

1.3 Getting and installing DND

In the actual stage you can only get the Xt interface for DND. If you want to use DND in non-Xt applications, you must write some code. It is not a difficult task to do so (see section The DND internals ).

The best way to install the DND Xt interface library is the following:

Get the OffiX package. It can be found at http://gutenberg.lcmi.ufsc.br/OffiX
Unpack the file somewhere. Edit the file Imake.options to suit your needs. If you don't want any OffiX utility installed, don't compile the OffiX modules (remove all from OFFIX_MODULES option).
Type the command xmkmf ; make Makefiles ; make
As root, type make install
As root, type make install.man

Now you should have the static DND library and the necessary header files installed on your system. If you are not root and want to compile your program with DND, just copy the files DragAndDrop.c and the DND header files from the OffiX directory and compile and link them with your program.

1.4 DND and window managers

There seems to be a strange behaviour when DND programs run under OpenWindows, at least under the version I have in my work. With FVWM there are no problems reported yet. If you run DND programs under another window manager, please send me a note telling about the results.

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