To see how the component objects are used in a chart object, let’s take another look at our Temperatures Chart (see Figure 5.14). Instead of constructing this chart from an IlvCartesianChart object (see Creating a Simple Cartesian Chart), we are going to construct it from an IlvChartGraphic object, the base object that allows us to display a chart.

Figure 5.15 shows the component objects that are needed to display this chart. When we created the chart using an IlvCartesianChart object, we set the following objects by hand:

If we use an IlvChartGraphic object instead of an IlvCartesianChart object, we must set the following objects as well:

The layout object does not need to be set since an instance is created by default when you create an IlvChartGraphic object.

To create our Temperatures Chart from an IlvChartGraphic object, we will again follow the basic steps presented in Creating a Simple Cartesian Chart. However, we must replace the step Creating a Cartesian Chart with the following series of tasks:

All the other tasks that are described in the paragraph Creating a Simple Cartesian Chart remain the same.

The complete source code of the example can be found in the chartgraphic.cpp file located in the $ILVHOME/samples/charts/userman/src directory.

To create a chart graphic object, use the following code:

The IlvRect object passed as a parameter corresponds to the bounding box of the created chart.

Since the data to be displayed with our chart are expressed in Cartesian coordinates, the projector that is set is an instance of the IlvCartesianProjector class.

We indicate the orientation of the scales as a parameter: the abscissa scale is oriented toward the right of the screen and the ordinate scale is oriented toward the top. All orientations that keep the abscissa and the ordinate scale(s) orthogonal are possible.

Use the following code to create the coordinate information for the abscissa:

The created coordinate information is associated with a coordinate. The type of this coordinate is passed as a parameter to the constructor used to create this coordinate information. By default, the minimum and maximum values that will be considered for the scale that represents this coordinate are automatically computed from the abscissa values of the data that have to be displayed by the created chart. This is done so that all the defined data can be displayed.

To define the abscissa scale displayer, perform the following steps:

To create the coordinate information for the ordinate, use the following code:

The created coordinate information is associated with a coordinate. The type of this coordinate is passed as a parameter to the constructor used to create this coordinate information. By default, the minimum and maximum values that will be considered for the scale that represents this coordinate are automatically computed from the ordinate values of the data that have to be displayed along this scale. This is done so that all the defined data that have to be displayed along this scale can be displayed.

To define the ordinate scale displayer, perform the following steps:

At this point, we have now completed creating our Cartesian chart from an IlvChartGraphic object. The chart we obtain is the same as the one shown in Figure 5.7. You can readily see the difference in using an IlvChartGraphic object instead of using an IlvCartesianChart object. Many more lines of code were required to instantiate the same chart object that we obtained by using a single line of code: