Labels plugin

Version: 6.3

Charba provides out of the box the feature to enable Labels which is a light weight plugin to display labels on pie, doughnut, polar area and bar chart (former name was PieceLabel).

info

The plugin has been heavily changed in order to be compliant with Chart.JS version 3.x) in the Charba project because the original project is unmaintained.

Activation

The labels plugin is injected directly in the document.

The plugin ID is a constant everywhere available, LabelsPlugin.ID, in LabelsPlugin entry point.

This plugin registers itself globally, meaning that once injected, all charts will display labels. In case you want it enabled only for a few charts, you can enable it as following:

// --------------------------------------
// enabling the plugin without any parameter
// the plugin is NOT registered to all charts
// --------------------------------------
LabelsPlugin.enable();

// --------------------------------------
// enabling the plugin with `true` parameter
// the plugin is registered to all charts
// --------------------------------------
LabelsPlugin.enable(true)

To activate the plugin in a specific chart, it's enough to provide the configuration options (see below) or enabling it by:

// --------------------------------------
// ENABLING the plugin to a chart instance 
// storing a plugin options 
// --------------------------------------
// creates a plugin options
LabelsOptions options = new LabelsOptions();
// creates a label by "myLabel" id
Label label = options.createLabel("myLabel");
// sets the render
label.setRender(Render.LABEL);
// stores the plugin options directly by the options
options.store(chart);

// --------------------------------------
// ENABLING the plugin to a chart instance 
// by a boolean using default plugin 
// options
// --------------------------------------
chart.getOptions().getPlugins().setEnabled(DataLabelsPlugin.ID, true);

Configuration

The plugin options can be changed at 2 different levels and are evaluated with the following priority:

per chart by chart.getOptions().getPlugins().setOptions method
or globally by Defaults.get().getGlobal().getPlugins().setOptions method

The configuration LabelsOptions class is the entry point of plugin configuration.

Every label configuration can be add to the LabelsOptions, assigning a unique id.

The id of a label configuration can be set by a string or by a specific class, LabelId.

// ------------------------
// CONFIGURES the label by
// LabelId id
// ------------------------
// creates a plugin options
LabelsOptions options = new LabelsOptions();
// creates label id
LabelId labelId = LabelId.create("myLabel1");
// creates and adds a label by "myLabel1" id
Label label = options.createLabel(labelId);
// sets the render
label.setRender(Render.PERCENTAGE);
... // additional label configuration
// stores the plugin options directly by the options
options.store();

The below example is showing how to create and add 2 labels (each one must have a unique id):

// ------------------------
// CONFIGURES the multiple 
// labels
// ------------------------
// creates a plugin options
LabelsOptions options = new LabelsOptions();
// creates and adds a label by "myLabel1" id
Label label1 = options.createLabel(LabelId.create("myLabel1"));
// sets the render
label1.setRender(Render.LABEL);
... // additional label configuration
// creates and adds a label by "myLabel2" id
Label label2 = options.createLabel("myLabel2");
// sets the render
label2.setRender(new RenderCallback(){
            
    @Override
    public String invoke(LabelsContext context){
        return "$$ "+ (int)(context.getValue() * context.getPercentage() / 100);
    }
});
... // additional label configuration
// stores the plugin options directly by the options
options.store();

You can also change the default for all charts instances, as following:

// creates a plugin options
LabelsOptions options = new LabelsOptions();
// creates a label by "myLabel" id
Label label = options.createLabel("myLabel");
// sets the render
label.setRender(Render.LABEL);

// --------------------------------------
// STORING plugin options
// --------------------------------------
// stores the plugin options by plugin ID
Defaults.get().getGlobal().getPlugin().setOptions(LabelsPlugin.ID, options);
// stores the plugin options without plugin ID
Defaults.get().getGlobal().getPlugin().setOptions(options);
// stores the plugin options directly by the options
options.store();

If you need to read the plugin options, there is the specific factory, LabelsOptionsFactory as static reference inside the LabelsPlugin entry point which can be used to retrieve the options from chart as following:

// gets options reference
LabelsOptions options;

// --------------------------------------
// GETTING plugin options from chart
// --------------------------------------
if (chart.getOptions().getPlugin().hasOptions(LabelsPlugin.ID)){
   // retrieves the plugin options by plugin ID
   options = chart.getOptions().getPlugin().getOptions(LabelsPlugin.ID, LabelsPlugin.FACTORY);
   //retrieves the plugin options without plugin ID
   options = chart.getOptions().getPlugin().getOptions(LabelsPlugin.FACTORY);
}

You can access to the configured labels configurations as following:

// ------------------------
// GETS the configured 
// labels
// ------------------------
// retrieves the plugin options by plugin ID
LabelsOptions options = chart.getOptions().getPlugin().getOptions(LabelsPlugin.FACTORY);
// gets all labels configurations
List<Label> allLabels = options.getLabels();
// gets "myLabel1" label configuration
Label label1 = options.getLabel(LabelId.create("myLabel1"));
// gets "myLabel2" label configuration
Label label2 = options.getLabel("myLabel2");

Options

The following options can configure how the labels will look like and they can be applied to the label object.

// creates a plugin options
LabelsOptions options = new LabelsOptions();
// creates label id
LabelId labelId = LabelId.create("myLabel1");
// creates and adds a label by "myLabel1" id
Label label = options.createLabel(labelId);
// sets the render
label.setRender(Render.LABEL);

The complete options are described by following table:

Name	Type	Default	Scriptable	Description
arc	boolean	`false`	-	If `true`, draws label in arc. Bar chart ignores this.
color	String - IsColor	default color	Yes	The font color of the label.
font	Font	default font	Yes	The font of label text.
images	Img[]	`null`	-	Set images when the rendering is set to Render.IMAGE.
outsidePadding	int	2	-	Add padding when the position is Position.OUTSIDE.
overlap	boolean	`true`	-	Draw label even it's overlap. Bar chart ignores this.
position	Position	Position.DEFAULT	-	Position to draw label. Bar chart ignores this.
precision	int	0	-	Precision for percentage label text.
render	Render	Render.PERCENTAGE	Yes	The value of the label to render.
shadowBlur	int	6	-	The label text shadow intensity.
shadowOffsetX	int	3	-	The label text shadow X offset.
shadowOffsetY	int	3	-	The label text shadow Y offset.
shadowColor	String - IsColor	rgba(0,0,0,0.3) -	-	The label text shadow color.
showActualPercentages	boolean	`false`	-	Show the real calculated percentages from the values and don't apply the additional logic to fit the percentages to 100 in total.
showZero	boolean	`false`	-	Identifies whether or not labels of value 0 are displayed
textMargin	int	2	-	The added margin of text when the position is Position.OUTSIDE or Position.BORDER.
textShadow	boolean	`false`	-	If `true`, draws the text shadows under labels.

Scriptable

Scriptable options in the plugin configuration accept a callback which is called for each of the underlying data values.

There are 3 options which can be defined as scriptable:

color, to set the color of the label.
font, to set the font of the label.
render, to set the value of the label to render.

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

The context object contains the following properties:

Name	Type	Description
active	boolean	Whether the associated element is hovered.
attributes	NativeObjectContainer	User object which you can store your options at runtime.
chart	IsChart	Chart instance.
dataIndex	int	The index of the current data.
dataItem	DataItem	The value of the label.
datasetIndex	int	The index of the current data set.
datasetItem	DatasetItem	The data set information for this data
element	ChartElement	The element (point, arc, bar, etc.) for this data
label	String	The string representation of the value of the label.
labelOptions	Label	The label configuration where the options is defined as scriptable.
mode	TransitionMode	The update mode, brought by conte
percentage	double	The percentage representation of the value of the label.
type	ContextType	The type of the context. It can be ONLY `ContextType.LABELS`.

The following options can be set by a callback:

Name	Callback	Returned types
color	ColorCallback<AnnotationContext>	String - IsColor
font	FontCallback<AnnotationContext>	FontItem
render	RenderCallback	String

Color

You can set the color of the labels at runtime, providing different colors for different labels.

The color property can be set as scriptable option, as following:

// creates a plugin options
LabelsOptions options = new LabelsOptions();
// creates label id
LabelId labelId = LabelId.create("myLabel");
// creates and adds a label by "myLabel" id
Label label = options.createLabel(labelId);
// sets callback
label.setColor(new ColorCallback<LabelsContext>(){

    /**
     * Called to change font color at runtime.
     * 
     * @param context callback context
     * @return a font color instance
     */         
    @Override
    public IsColor invoke(LabelsContext context){
        return context.getDataIndex() % 2 == 0 ? 
            HtmlColor.BLACK : 
            HtmlColor.RED;
    }
});

Font

You can set the font of the labels at runtime, providing different font for different labels.

The font property can be set as scriptable option, providing a font item instance, as following:

// creates a plugin options
LabelsOptions options = new LabelsOptions();
// creates label id
LabelId labelId = LabelId.create("myLabel");
// creates and adds a label by "myLabel" id
Label label = options.createLabel(labelId);
// sets callback
label.setColor(new FontCallback<LabelsContext>(){

    /**
     * Called to set the label font at runtime.
     * 
     * @param context callback context
     * @return a font instance
     */ 
   @Override
   public Font invoke(LabelsContext context){
      FontItem fontItem = new FontItem();
      int size = context.getDataIndex() % 2 == 0 ? 32 : 12;
      fontItem.setSize(size);
      return fontItem;
   }
});

Render

You can set the value of the labels to show on the chart at runtime, providing different values for different labels.

The render property can be set as scriptable option, as following:

// creates a plugin options
LabelsOptions options = new LabelsOptions();
// creates label id
LabelId labelId = LabelId.create("myLabel");
// creates and adds a label by "myLabel" id
Label label = options.createLabel(labelId);
// sets callback
label.setRender(new RenderCallback<LabelsContext>(){

    /**
     * Called to set the label render at runtime.
     * 
     * @param context callback context
     * @return a font instance
     */ 
    @Override
    public String invoke(LabelsContext context){
        return context.getDataIndex() % 2 == 0 ? 
            "Percentage: "+context.getPercentage() : 
            "Value: "+context.getDataItem().getValue();
    }
});

Options builder

Charba provides a builder to create options using the set methods in sequence and get the options object at the end of configuration.

// creates a plugin options
LabelsOptions options = LabelsOptionsBuilder.create()
    .createLabel("myLabel")  // entry to label builder
    .setRender(Render.PERCENTAGE)
    .setColor(HtmlColor.WHITE)
    .setPrecision(2)
    .getOptionsBuilder() // return to options builder
    .build();
// sets options
chart.getOptions().getPlugins().setOptions(LabelsPlugin.ID, options);

Creating a build by LabelsOptionsBuilder.create() it will use the global options as default, instead by LabelsOptionsBuilder.create(chart) it will use the global chart options as default.

Labels plugin​

Activation​

Configuration​

Options​

Scriptable​

Color​

Font​

Render​

Options builder​