/*!
     \example examples/donutbreakdown
     \title Donut chart breakdown example
     \subtitle

     This example shows how to use create a donut breakdown chart using QPieSeries API.
     \image examples_donutbreakdown.png

     Let's start by defining some data for the chart.

     \snippet ../examples/donutbreakdown/main.cpp 1

     Then we create a chart where we add the data. Note that this is our own chart derived from QChart.

     \snippet ../examples/donutbreakdown/main.cpp 2

     Our own chart works so that in the constructor we create a main series
     which aggregates the data provided by the breakdown series. This is the piechart in the center.

     \snippet ../examples/donutbreakdown/donutbreakdownchart.cpp 1

     When a breakdown series is added the data is used to create a slice in the main series and the
     breakdown series itself is used to create a segment of a donut positioned so that it is aligned
     with the corresponding slice in the main series.

     \snippet ../examples/donutbreakdown/donutbreakdownchart.cpp 2

     Here's how the start and end angles for the donut segments are calculated.

     \snippet ../examples/donutbreakdown/donutbreakdownchart.cpp 3

     Legend markers are customized to show the breakdown percentage and markers for the main level slices are hidden.

     \snippet ../examples/donutbreakdown/donutbreakdownchart.cpp 4

     Instead the main level slices show the percentage on the label.

     \snippet ../examples/donutbreakdown/mainslice.cpp 1
     \snippet ../examples/donutbreakdown/mainslice.cpp 2

     And now that we have our chart defined we can finally create a QChartView and show the chart.

     \snippet ../examples/donutbreakdown/main.cpp 3

*/