Bubble

Bubble is one of Pablo's display functional units.  It accepts a vector or
two-dimensional array of input values and represents the data as individual
colored circles within a grid accessible by row/column indexing.  Each 
bubble is filled with a color according to the magnitude of the incoming
data.  Bubble possesses minimum and maximum data values that can be set
by the user during the configuration process.

The top-left square of the bubble plotting area is defined as location (0,0).
Columns grow toward the right and rows increase downward.  Vectors are 
displayed as a single row of bubbles.

Clicking the left mouse button with the cursor inside the bubble invokes a
callback displaying the current value at that (row,column) location and
also the row and column location of the click.

Functional Unit Inputs:  One-Dimension or Two-Dimension Array
                         Vector Index and Element Value of Changed Cell
                         Array Indicies and Element Value of Changed Cell

Bubble attributes:

	XtNheight	height (in pixels) of the bubble widget
	XtNwidth	width (in pixels) of the bubble widget
	XtNbackground	the background color of the widget
	XtNgridColor	color of the grid lines drawn in a contour
	XtNnumColors	number of colors in the bubble colormap
	XtNrows		number of row elements in the matrix
	XtNcolumns	number of column elements in the matrix
	XtNshowGrid	set to true if grid lines are to be drawn on the
				plot area
	XtNminValue	minimum data value displayed by the widget
	XtNmaxValue	maximum data value displayed by the widget
