Interactivity with xtpanel

Using xtpanel from within a seismic processing program offers some advantages. In the filtering example above, because the entire process is re-run each time a parameter is changed, a lot of extra work is done. Each time the RUN button is pressed, the input dataset (containing a single impulse) is recreated. Then the filter program must read in the data, as well as the parameters necessary to run the job. In such a trivial example, this extra work does not take much time. But in larger tasks, the extra overhead required to completely re-run a job may make the interactive performance poor.

To solve this problem, we devised a way to use xtpanel from within a processing program. After reading in its data and getting set up to run, a program brings up an xtpanel containing objects that specify some of the program parameters. Then the program waits for input from the xtpanel. When input is received, the program executes, and then waits for additional panel input. Additional panel input causes the program to be re-run, but without having to do all the overhead that was done at the start of the program.

The first program to use this interaction is a seismic data cube viewing program called Cubeplot. Cubeplot displays a perspective view of a seismic data cube. Displayed on the three faces of the cube are slices taken from within the data volume. In its standard batch mode of execution, the user specifies on the command line the three slices to be shown. If, on the command line, the user specifies popup=y, then a panel containing three sliders appears. As the user changes a slider, a different data slice is displayed on one of the three cube faces.

The xtpanel script is built into the C language source code for Cubeplot. Here is the script:

button={ label=Quit action="PRINTQUIT" action=QUIT }
vbox={
  hbox={ name=noborder width=400
    message={ value=axis-1 }
    scrollbar={ label="axis 1" name=pan1 min=0 max=N1 format="%.0f"
      width=300 value=FRAME1
      action="ASSIGN val1 $val"
      action="PRINT frame1=$(pan1) frame2=$(pan2) frame3=$(pan3)"
    }
    message={ name=val1 value=FRAME1  }
  }
  hbox={ name=noborder width=400
    message={ value=axis-2 }
    scrollbar={ label="axis 2" name=pan2 min=0 max=N2 format="%.0f"
      width=300 value=FRAME2
      action="ASSIGN val2 $val"
      action="PRINT frame1=$(pan1) frame2=$(pan2) frame3=$(pan3)"
    }
    message={ name=val2 value=FRAME2  }
  }
  hbox={ name=noborder width=400
    message={ value=axis-3 }
    scrollbar={ label="axis 3" name=pan3 min=0 max=N3 format="%.0f"
      width=300 value=FRAME3
      action="ASSIGN val3 $val"
      action="PRINT frame1=$(pan1) frame2=$(pan2) frame3=$(pan3)"
    }
    message={ name=val3 value=FRAME3  }
  }
}

However, the user can substitute a different script, containing whatever program parameters are of interest. Here are the instructions that appear in the on-line program documentation:

popup   Specifying popup=y brings up an xtpanel (if you have xtpanel
	installed) with three sliders. Moving these sliders changes
	the frames plotted on the three cube faces. If you pipe
	the output of Cubeplot to "Xtpen cachepipe=n" you will see
	the display update as the sliders are moved.
	You can specify your own xtpanel script file by doing
	popup_file=filename.

The program then calls two subroutines: popup_start brings up the xtpanel. This is called after the program's preliminary work (reading in the input data, getting parameter values, etc.) has been done. A second routine, popup_check is called after each pass through processing the data. This routine waits for output from the xtpanel. It then adds the new output to the table of parsed command line arguments. I.e. if the user moves a slider and the xtpanel prints ``frame1=100'' then after popup_check it is as though ``frame1=100' had been specified on the command line. When this routine returns the program reprocesses the data (in the case of Cubeplot case plotting a new figure) using the new parameters.

Users interested in the details of these routines are referred to the CD-ROM version of this report, where the source code for Cubeplot and the popup routines is contained. The most important point to make about the source is that the modifications to the Cubeplot program were quite small -- just two subroutine calls, and a few lines to interpret the new parameter values that come back from the panel. Interaction can easily be added to any program in this way.

Figure  displays a typical interactive session using the built-in xtpanel interaction of Cubeplot. If you are reading the report on CD-ROM, pressing the button at the end of the figure caption will bring up this example. Moving the sliders will change the display.

It is worth noting that although Cubeplot is a C language program, the xtpanel popup facility can just as easily be used from within Fortran and Ratfor programs.

 

cubeplot
Figure 2 Interactive Cubeplot session using xtpanel. The xtpanel is brought up from within the program. Each time a slider is moved, a subroutine is run to re-draw the image. CD-ROM readers can click on the button at the end of this caption to run Cubeplot.