Doughnut chart

(quoted from Doughnut chart definition in Wikipedia)

A doughnut chart is a variant of the pie chart, with a blank center allowing for additional information about the data as a whole to be included. Doughnut charts are similar to pie charts in that their aim is to illustrate proportions. This type of circular graph can support multiple statistics at once and it provides a better data intensity ratio to standard pie charts.

A doughnut charts are the same of pie charts and then divided in the segments, the arc of each segment shows the proportional value of each piece of data.

They are excellent at showing the relational proportions between data.

Programmatically, you could use a doughnut chart as following:

// creates the chart    
DoughnutChart chart = new DoughnutChart();
// adds to DOM
component.add(chart);
...
// example for Elemental2
// gets the chart instance as DOM element
Element element = chart.getChartElement().as();
// adds to DOM
DomGlobal.document.body.appendChild(element);

By UIBinder (ONLY for GWT), you could use a doughnut chart as following:

<ui:UiBinder xmlns:ui="urn:ui:com.google.gwt.uibinder"
   xmlns:g="urn:import:com.google.gwt.user.client.ui"
   xmlns:c="urn:import:org.pepstock.charba.client.gwt.widgets">

   <g:HTMLPanel  width="100%">
      ....
      <c:DoughnutChartWidget ui:field="chart"/>
      ...
   </g:HTMLPanel>
</ui:UiBinder> 

Dataset

The doughnut chart allows to define the data and a number of properties, used to display the data, by a doughnut dataset.

Every chart has got a method to create a typed dataset accordingly with the chart type. The dataset can be also created instantiating the constructor.

// creates the chart
DoughnutChart chart = new DoughnutChart();
// creates the dataset
DoughnutDataset dataset = chart.newDataset();
// sets the option
dataset.setBackgroundColor(HtmlColor.RED);
...
// creates the dataset
DoughnutDataset datasetNew = new DoughnutDataset();
// sets the option
datasetNew.setBackgroundColor(HtmlColor.RED);
...
// sets the datasets to the chart
chart.getData().setDatasets(dataset, datasetNew);

The following are the attributes that you can set:

Name	Type	Scriptable	Description
backgroundColor	String[] - IsColor[] - Pattern[] - Gradient[]	Yes	The fill color/pattern of the arcs in the dataset.
borderAlign	BorderAlign	Yes	The borders alignment of arcs.
borderColor	String[] - IsColor[] - Gradient[]	Yes	The border color of the arcs in the dataset.
borderJoinStyle	JoinStyle[]	Yes	Arc line joint style. See MDN.
borderRadius	int[] - ArcBorderRadius[]	Yes	The arc border radius (in pixels).
borderWidth	int[]	Yes	The border width of the arcs in the dataset.
circumference	double	-	Sweep to allow arcs to cover. For default value, see doughnuts options.
clip	boolean - double - Clip	-	How to clip relative to chart area. Positive value allows overflow, negative value clips that many pixels inside chart area.
hoverBackgroundColor	String[] - IsColor[] - Pattern[] - Gradient[]	Yes	The fill color/pattern of the arcs when hovered.
hoverBorderColor	String[] - IsColor[] - Gradient[]	Yes	The stroke color of the arcs when hovered.
hoverBorderJoinStyle	JoinStyle[]	Yes	Arc line joint style, when hovered. See MDN.
hoverBorderWidth	int[]	Yes	The stroke width of the arcs when hovered.
hoverOffset	int	Yes	The offset of the arc (in pixels) when hovered.
label	String	-	The label for the dataset.
offset	int	Yes	The offset of the arc (in pixels).
normalized	boolean	-	If true, you provide data with indices that are unique, sorted, and consistent across data sets and provide the normalized.
rotation	double	-	Starting angle to draw arcs from. For default value, see doughnuts options.
parsing	boolean	-	If false, the data set parsing is disable. If parsing is disabled, data must be sorted and in the formats the associated chart type and scales use internally.
spacing	int	-	Fixed arc offset (in pixels). Similar to offset but applies to all arcs.
weight	double	-	The relative thickness of the dataset. Providing a value for weight will cause the doughnut dataset to be drawn with a thickness relative to the sum of all the dataset weight values.

General

The general options for a doughnut dataset can control behaviors not related to styling or interactions and they are the following:

Name	Defaults	Description
clip	Undefined.DOUBLE	How to clip relative to chart area.
label	null	The label for the dataset.
normalized	false	If true, you provide data with indices that are unique, sorted, and consistent across data sets and provide the normalized.
parsing	true	If false, the data set parsing is disable. If parsing is disabled, data must be sorted and in the formats the associated chart type and scales use internally.

info

label options is just a pure label to add to the dataset and is NOT the label for the dataset which appears in the legend and tooltips.

Styling

The style of each arc of the dataset can be configured by the following properties:

Name	Description
backgroundColor	The fill color of the arcs in the dataset.
borderAlign	The borders alignment of arcs.
borderColor	The border color for arcs.
borderJoinStyle	Arc line joint style
borderRadius	The arc border radius (in pixels).
borderWidth	The width of the arc border in pixels.
offset	The offset of the arc (in pixels).
spacing	Fixed arc offset (in pixels). Similar to offset but applies to all arcs.
weight	The relative thickness of the dataset.

All above options have got the fallback to the associated Arc elements, retrievable by the following statements:

// from chart instance
Arc arc = chart.getOptions().getElements().getArc();
// sets options for all pie datasets of the chart
arc.setOffset(6);
...
// from defaults
Arc defaultArc  = Defaults.get().getGlobal().getElements().getArc();
// sets options for all pie datasets of all charts
defaultArc.setOffset(6);

Interactions

The interaction with each arc can be controlled with the following properties:

Name	Description
hoverBackgroundColor	The fill color of the arcs in the dataset when hovered.
hoverBorderColor	The border color for arcs when hovered.
hoverBorderJoinStyle	Arc line joint style when hovered.
hoverBorderWidth	The width of the arc border in pixels when hovered.
hoverOffset	The offset of the arc (in pixels) when hovered.

All above options have got the fallback to the associated Arc elements, retrievable by the following statements:

// from chart instance
Arc arc = chart.getOptions().getElements().getArc();
// sets options for all pie datasets of the chart
arc.setOffset(6);
...
// from defaults
Arc defaultArc  = Defaults.get().getGlobal().getElements().getArc();
// sets options for all pie datasets of all charts
defaultArc.setOffset(6);

Scriptable

Scriptable options at dataset level accept a callback which is called for each of the underlying data values. See more details in Configuring charts section.

// creates chart
DoughnutChart chart = new DoughnutChart();
// creates dataset
DoughnutDataset dataset = chart.newDataset();
// sets the option by a callback 
dataset.setBackgroundColor(new ColorCallback<DatasetContext>(){

   @Override
   public IsColor invoke(DatasetContext context){
      // logic
      return color;
   }
});

The following options can be set by a callback:

Name	Callback	Returned types
backgroundColor	ColorCallback<DatasetContext>	String - IsColor - Pattern - Gradient
borderAlign	BorderAlignCallback	BorderAlign
borderColor	ColorCallback<DatasetContext>	String - IsColor - Gradient
borderJoinStyle	JoinStyleCallback<DatasetContext>	JoinStyle
borderRadius	BorderRadiusCallback<DatasetContext>	int - ArcBorderRadius
borderWidth	WidthCallback<DatasetContext>	int
hoverBackgroundColor	ColorCallback<DatasetContext>	String - IsColor - Pattern - Gradient
hoverBorderColor	ColorCallback<DatasetContext>	String - IsColor - Gradient
hoverBorderJoinStyle	JoinStyleCallback<DatasetContext>	JoinStyle
hoverBorderWidth	WidthCallback<DatasetContext>	int
hoverOffset	OffsetCallback<DatasetContext>	int
offset	OffsetCallback<DatasetContext>	int

Data structure

The data of a dataset for a doughnut chart is specified as a an array of numbers. Each point in the data array corresponds to the label at the same index.

// sets data as an array of doubles
dataset.setData(1,2,3,4,6);

// sets data as a list of double
List<Double> list = new LinkedList<>();
list.add(1);
list.add(2);
list.add(3);
dataset.setData(list);

To provide context of what each point means, we include an array of strings that show around each point in the chart.

...
chart.getData().setLabels("label1", "label2");
...

Options

The doughnut chart defines specific options implementation to be configured. These options are merged with the global chart configuration options to form the options passed to the chart.

// creates chart
DoughnutChart chart = new DoughnutChart();
// gets the chart options
DoughnutOptions options = chart.getOptions();
// sets options
options.setResponsive(true);
options.setCircumference(180D);

These are the options specific to doughnut charts:

Name	Type	Default	Description
circumference	double	360	Sweep to allow arcs to cover.
cutoutPercentage	String	50%	The percentage of the chart that is cut out of the middle. It's a string, ending with '%', as percentage of the chart radius.
cutout	double	Undefined.DOUBLE	The portion of the chart that is cut out of the middle, in pixels.
radiusPercentage	String	100%	the outer radius of the chart. It's a string, ending with '%', as percentage of the maximum radius.
radius	double	Undefined.DOUBLE	The outer radius of the chart, in pixels.
rotation	double	0	Starting angle to draw arcs from.