Gauge chart

A gauge chart is Charba extension of doughnut chart, by a controller implementation.

The gauge charts are divided in the segments, the arc of each segment shows the proportional value of data.

Programmatically, you could use a gauge chart as following:

// creates the chart    
GaugeChart chart = new GaugeChart();
// 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 gauge 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:GaugeChartWidget ui:field="chart"/>
      ...
   </g:HTMLPanel>
</ui:UiBinder> 

Dataset

The gauge chart allows a number of properties to be specified for the gauge dataset.

// creates the chart
GaugeChart chart = new GaugeChart();
// creates the dataset
GaugeDataset dataset = chart.newDataset();
// sets the value
dataset.setValue(90.5D);
// sets thresholds
dataset.setThresholds(DefaultThreshold.NORMAL.getThreshold().setValue(40), 
    DefaultThreshold.WARNING.getThreshold().setValue(75), 
    DefaultThreshold.CRITICAL.getThreshold().setValue(100));
// sets the dataset to the chart
chart.getData().setDatasets(dataset);

The following are the attributes that you can set:

Name	Type	Default	Description
borderColor	String - IsColor	color option value	The border color of the arcs in the dataset.
borderRadius	int - ArcBorderRadius	0	The arc border radius (in pixels).
borderWidth	int	0	The border width of the arcs in the dataset.
emptyColor	String[] - IsColor[]	rgb(234,234,234) -	The color to fill the segment of the chart which represents the empty part.
percentageThreshold	boolean	true	If true, it uses the percentage as threshold instead of the value.
thresholds	Threshold[]	[]	The thresholds to apply to the gauge dataset.

caution

A gauge chart can have ONLY 1 dataset.

The dataset can be created instantiating the constructor, passing the maximum value of chart.

The default value of maximum value is 100.

// sets max value
int maxValue = 200;
// creates the chart
GaugeChart chart = new GaugeChart();
// creates the dataset with new max value
GaugeDataset dataset = chart.newDataset(maxValue);
// sets the value
dataset.setValue(90.5D);
// sets the dataset to the chart
chart.getData().setDatasets(dataset);

Using thresholds

The thresholdsis the entity which defines the color of the dataset, based on the value of the threshold.

A threshold is composed by 3 attributes:

• name, mandatory attribute to apply the name, for instance "warning".
• value, optional attribute to set the value, the default is Double.MAX_VALUE.
• color, optional attribute to set the color to use in the data set when the threshold is activated y the value of data set, the default is rgb(140, 214, 16) -         .

The below example is configuring the chart in order to use

• green color if the value of dataset is less or equals to 50,
• yellow color if the value of dataset is less or equals to 75 and greater than 50,
• red color if the value of dataset is greater than 75 (set to 100 because it's the maximum value of the data set).

Threshold myNorm = new Threshold("normal", 50, HtmlColor.GREEN);
Threshold myWarn = new Threshold("warning", 75, HtmlColor.YELLOW);
Threshold myCrit = new Threshold("critical", 100, HtmlColor.RED);
// creates the chart
GaugeChart chart = new GaugeChart();
// creates the dataset
GaugeDataset dataset = chart.newDataset();
// sets the thresholds
dataset.setThresholds(myNorm, myWarn, myCrit); 
// sets the dataset to the chart
chart.getData().setDatasets(dataset);

Charba provides a default threshold implementation by gauge threshold enumeration.

Threshold instance	Name	Value	Color
DefaultThreshold.NORMAL	"NORMAL"	75	rgb(140, 214, 16) -
DefaultThreshold.WARNING	"WARNING"	90	rgb(239, 198, 0) -
DefaultThreshold.CRITICAL	"CRITICAL"	Double.MAX_VALUE	rgb(231, 24, 49) -

You can reuse the gauge threshold enumeration, changing color or value or both.

Threshold myNorm = DefaultThreshold.NORMAL.getThreshold().setValue(50).setColor(HtmlColor.GREEN);
Threshold myWarn = DefaultThreshold.WARNING.getThreshold().setValue(75).setColor(HtmlColor.YELLOW);
Threshold myCrit = DefaultThreshold.WARNING.getThreshold().setValue(100).setColor(HtmlColor.RED);
// creates the chart
GaugeChart chart = new GaugeChart();
// creates the dataset
GaugeDataset dataset = chart.newDataset();
// sets the thresholds
dataset.setThresholds(myNorm, myWarn, myCrit); 
// sets the dataset to the chart
chart.getData().setDatasets(dataset);

Labels

The gauge charts allow you to set labels inside the chart in order to improve the understanding of the chart for the user.

There are 2 possible labels you can set in the chart:

Value label

The value label allows you to show the value or percentage inside the chart.

// creates the dataset
GaugeDataset dataset = chart.newDataset();
// sets the percentage rendering
dataset.getValueLabel().setPercentage(true);

The value label element contains all options in order to configure the rendering.

The following are the attributes that you can set:

Name	Type	Default	Scriptable	Description
animated	boolean	false	-	If the rendered label will be shown based on the animation of chart.
autoFontSize	boolean	true	-	If true, the font size to applied to the rendered label is automatically calculated at runtime, otherwise uses the size property of the font.
color	IsColor	rgb(128, 128, 128) -	Yes	Color of the content.
display	boolean	true	-	If true, the value label is shown.
font	IsFont	null	Yes	Font of rendered label. If autoFontSize is set to true, the size property is ignored because automatically calculated at runtime. The default value is the font instance in the chart options. See Font.
format	MeterFormatCallback	null	Yes	The callback instance which format the value.
percentage	boolean	false	-	If true, the rendered label will show the dataset value as a percentage.
precision	int	2	-	The amount to decimals digits to apply to the value.

Description label

The description label allows you to show a string as description inside the chart, below the value label.

// creates the dataset
GaugeDataset dataset = chart.newDataset();
// enables rendering
dataset.getDescriptionLabel().setDisplay(true);
// enables rendering
dataset.getDescriptionLabel().setContent("RAM utilization");

The description label element contains all options in order to configure the rendering.

caution

This label only apply if display options of value label is true.

The following are the attributes that you can set:

Name	Type	Default	Scriptable	Description
autoFontSize	boolean	true	-	If true, the font size to applied to the rendered label is automatically calculated at runtime, otherwise uses the size property of the font.
color	IsColor	rgb(128, 128, 128) -	Yes	Color of the content.
content	String	null	Yes	The content of description label.
display	boolean	false	-	If true, the value label is shown.
font	IsFont	null	Yes	Font of rendered label. If autoFontSize is set to true, the size property is ignored because automatically calculated at runtime. The default value is the font instance in the chart options. See Font.

Data structure

The data of a dataset for a gauge chart is specified as single value.

// creates the dataset
GaugeDataset dataset = chart.newDataset();
// sets the value
dataset.setValue(90.5D);

caution

The setData methods are available, inherited by a doughnut dataset, but you can NOT use them otherwise an exception will throw.
Use setValue instead.

Options

The gauge chart defines the following configuration options. It extends the meter options.

To set the options at chart level, you can get a typed object accordingly with the chart type.

// creates the chart
GaugeChart chart = new GaugeChart();
// gets options
GaugeOptions options = chart.getOptions();
// sets options
options.setRender(Render.PERCENTAGE);
options.setPrecision(3);

See doughnut chart configuration how to configure the gauge chart, in addition of following options:

Name	Type	Default	Description
cutoutPercentage	String	"90%"	Immutable property, always "90%".
circumference	double	360	Immutable property, always 360.
rotation	double	0	Immutable property, always 0.

info

The gauge chart disables the legend, tooltips and animation components.

Scriptable

Scriptable options in the configuration accept a callback which is called for each animation cycle.

// creates the chart
GaugeDataset dataset = chart.newDataset();
// sets the color
dataset.getValueLabel().setColor(new ColorCallback<MeterContext>(){

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

The callbacks are getting the only 1 argument, the scriptable context which contains the context of the callback execution.

The context object contains the following properties:

Name	Type	Description
attributes	NativeObjectContainer	User object which you can store your options at runtime.
chart	IsChart	Chart instance.
datasetLabel	String	The label of the dataset.
easing	double	The easing of drawing (between 0 and 1) for animation.
type	ContextType	The type of the context. It can be ONLY ContextType.METER.
value	double	The value of meter or gauge dataset.

The gauge chart can provide scriptable options by the gauge data set and the labels.

The following options can be set by a callback:

Name	Callback	Returned types
color	ColorCallback<MeterContext>	String - IsColor
content	MeterContentCallback	String
font	FontCallback<MeterContext>	FontItem
format	MeterFormatCallback	String

Here is an example fo value formatting.

// creates the dataset
GaugeDataset dataset = chart.newDataset();
// sets the formatter
dataset.getValueLabel().setFormatCallback(new MeterFormatCallback(){

   @Override
   public String invoke(MeterContext context){
      // logic
      return Utilities.applyPrecision(context.getValue(), 0) + " logged users";
   }
});