Introduction

For several years, members of SEP have looked for a way to add interactivity to existing UNIX programs. The most ambitious project, SepView Dulac (1988), was a complete graphical interface environment and interface generator. SepView was not completed at SEP, where the necessary development time and expertise were not available. However, the work has been completed elsewhere.

Two simpler schemes were developed later -- IPE Cole (1990a) and xvpanel Cole (1990b).

IPE (an acronym for Interactive Processing Environment) had two serious limitations:

• It was a two-step process: a code generator, Ipemake, took in a simple ASCII description of a program's parameters, and generated C language code that had to be compiled into IPE. A new program was generated for each new interface added.
• IPE was tied to the pipeline processing model, after parameters were set the end result was always a simple pipeline of processes to be run.

Xvpanel was an improvement, in that the intermediate step of generating and compiling C code was eliminated. However, several problems remained:

• Written using the XView toolkit developed by Sun Microsystems, which is not very portable.
• The command line interface was unfriendly. All parameters had to be specified, in a particular order, or xvpanel would fail to work.
• Like IPE, still tied to the pipeline processing model.

Working from the base of experience gained in developing these earlier schemes we have written a new program, called xtpanel, that is more powerful, more flexible, and easier to use than these earlier programs. Xtpanel has none of the disadvantages of the earlier products, and has several advantages:

• Written using the X toolkit, included with all versions of X windows. Very portable.
• Has an easy to read, easy to use script language in which panels can be built.
• Not tied to the pipeline processing model. Panel objects can act independently of one another, or in concert.
• Comes with the xtpanel generator, a series of xtpanel scripts that guide a user through the process of building an xtpanel interactively.
• Comes with an interactive tour of some examples, as well as an interactive help facility.

While xtpanel only recently reached its present state, there are already a number of interesting geophysical projects that are using xtpanel. For example, Stan Ruppert, a Ph.D. student in Geophysics at Stanford, is modeling the shear wave velocity structure of the crust and upper mantle beneath the Colorado Plateau. Stan generates synthetic seismograms given a velocity model, and compares them against recorded seismograms. What was a tedious process, where Stan manually edited a velocity parameter file, then ran a batch program to generate the synthetic seismogram, was made interactive using xtpanel in the course of a few hours. Matthias Schwab, in this report Schwab (1992), uses xtpanel to build a tutorial on wavelet transforms. In addition to these specific projects, xtpanel is also used by several authors in this report to provide interactivity. Those reading the CD-ROM version of this report are able to click on buttons attached to most figures. In many cases, this will bring up an xtpanel that drives an interactive reproduction of the figure, perhaps giving the reader an opportunity to change some of the relevant parameters.

Later in this report, we illustrate the use of xtpanel with several examples. First, we describe xtpanel and its features in greater detail.