Working Widgets Without Code

Introduction

TSIPP is a 3-D image specification and rendering toolkit for use with Tcl and Tk used by the TSIPP Workbench. The main goal of TSIPP is visualization; the understanding of data in science or engineering (see ref. [2] p. 9). Towards this objective, the TSIPP Workbench can be used to create a class of megawidgets which:

have the appearance of visual scenes with photographic realism;
can vary with time (animation) or other control stimulus;
are interactive in that they may solicit input.

An example of this would be to create a "hydraulic widget" that indicates the water level in a reservoir. During an interactive session the image of the widget is defined, as well as the methods to be supported and their effect on the image. The result is a regular Tk widget that can be immediately used with minimal code (this file can be found in the "examples" directory, named "hydraulic_animate"):

#!/bin/sh
# standard executable Tcl file ...          \
exec tksipp "$0" "$@"
set env(TSIPPwb) [file dir [info script]]/..
lappend auto_path $env(TSIPPwb)/tcl
package require RLE_animate
class hydraulic {
    inherit RLE_animate
}
pack [hydraulic .r]             -side left
pack [scale     .s                          \
        -to      1                          \
        -from    [.r cget -n_frame]         \
        -command {.r show}                  \
        -label   "Water Level"] -side right

... which changes to ...

as the slider is moved.

The animation of the image encompasses more than just movements of the objects in the scene. Camera positions, positions of light sources, and the intensity and characteristics of the image can all be controlled by methods of the widget. In the following example, a representation of activity in a nuclear reactor is related to control rod position:

raise the control rods, and see that core cook! ...

Subsystem Interfaces

The TSIPP Workbench comprises an incr-Tcl program which interfaces to TSIPP, which at present is statically linked to the wish executable. This in turn provides a Tcl command interface to SIPP, the SImple Polygon Processor library. The state of the TSIPP Workbench can be saved as a plain-text incr-Tcl source file, which may be reloaded to restore the state of the tool. This Tcl source file can be thought of as the "source" for the image. As a human readable incr-Tcl program it provides the potential for interfacing to other image processing systems, or of implementing recovery from tool problems which make the file unreadable, which would be significantly more difficult if the image source was in binary format.

Still images may be written to a PPM format file, as defined by the PBMPlus toolkit, while animated images are written out as an RLE file, as defined by the Utah Raster Toolkit.

To fulfill its role as a widget creator, it is intended that the tool will generate incr-Tcl class definitions for a widget that has the appearance of the image as drawn, complete with methods which vary the appearance as defined using the tool. This has not yet been implemented, and as can be seen in the example code for the desk widget above, a standard widget is used through inheritance. The widget loads an RLE file with a name which by default is derived from the name of the widget, but may be specified explicitly as a parameter to the constructor.