Show()

The show function, Show(), displays the graph. It calls the Borland BGI functions, so it only works for the PC class video modes that Borland supports. Show() uses autodetection and positions the graph automatically. There is no way to save the graphics image. If you want to save it, you need a graphics screen grabber program such as GRAB from Word Perfect Corp. You really should write out the graphics matrix and use a better graphics program for professional quality.

Show() is a long routine with several major steps. The steps are

• Use auto-detection to find the graphics driver

• Initialize the graphics screen at its highest resolution, clear the screen, set the color to the highest color.

• Determine the screen dimensions, and line settings, write the titles, and determine the axis margins. Draw rectangle on the graph margins, if requested.

• Construct and display a YAxis object from the graph matrix and margins.

• Construct and display a XAxis object from the graph matrix and margins.

• Plot the data, and connect the points if requested. Draw the horizontal and vertical reference lines.

• Draw the axis labels, then clean up the pointers.

The interesting part of Show() is the axis objects. The axes will cover all of the data, and present neat axis numbers. The tick marks, positions, and values are calculated by Applied Statistics Algorithm 183. It is a translated FORTRAN program for calculating the scale, and values for an axis. This routine is fairly complicated, so I will refer you to the literature for it. It has three basic responsibilities: calculate the range for the axis labels, produce neat values, and fix up. The Axis will rescale the data by an offset and power so that the axis values will be neat. This information will appear next to the axis label if it was required.

The Axis class, Axis, is a base class for the XAxis and YAxis classes. Axis, supplies a virtual display function that is overloaded in the XAxis and YAxis objects. These objects are derived from Axis, so the Axis functions common to the X-Y axes are performed during the constructor call. The derived classes' main responsibility is to put the axis on the screen. The ticks and values are drawn relative to the viewports for the different axes.