Cartesian Linear Axes

The linear axis is use to chart numerical data. It can be placed on either the x or y axis.

Here are some example how to create linear axes:

// creates a linear axis with default scale id "y" and default kind "y" 
CartesianLinearAxis axis1 = new CartesianLinearAxis(chart);

// creates a linear axis with scale id "my-axis" and default kind "y" 
CartesianLinearAxis axis2 = new CartesianLinearAxis(chart, "my-axis");

// creates a linear axis with scale id "my-axis" and default kind "y" 
CartesianLinearAxis axis3 = new CartesianLinearAxis(chart, ScaleId.create("my-axis"));

// creates a linear axis with default scale id "y" and custom kind "y" 
CartesianLinearAxis axis4 = new CartesianLinearAxis(chart, AxisKind.Y);

// creates a linear axis with scale id "my-axis" and custom kind "y" 
CartesianLinearAxis axis5 = new CartesianLinearAxis(chart, "my-axis", AxisKind.Y);

// creates a linear axis with scale id "my-axis" and custom kind "y" 
ScaleId myAxis = ScaleId.create("my-axis");
CartesianLinearAxis axis6 = new CartesianLinearAxis(chart, myAxis, AxisKind.Y);

// adds axes to chart configuration
chart.getOptions().setAxes(axis1, ...);

Options

The cartesian linear axis allows to define a number of properties, used to display the data.

// creates a linear axis 
CartesianLinearAxis axis = new CartesianLinearAxis(chart);
// sets and gets the max value
axis.setMax(100);

double max = axis.getMax();

The following are the attributes that you can set:

Name	Type	Scriptable	Description
alignToPixels	boolean	Yes	Align pixel values to device pixels.
backgroundColor	String - IsColor	Yes	The background color of scale area.
beginAtZero	boolean	Yes	If true, scale will include 0 if it is not already included.
bounds	Bounds	Yes	Determines the scale bounds on axis.
display	boolean - Display	Yes	If Display.TRUE, the axis is shown.
grace	int	Yes	Amount of pixels for added room in the scale range above and below data.
graceAsPercentage	double	Yes	Sets a value, between 0 and 1, as percentage, for added room in the scale range above and below data.
max	double	Yes	User defined maximum number for the scale, overrides maximum value from data.
min	double	Yes	User defined minimum number for the scale, overrides minimum value from data.
offset	boolean	Yes	If true, extra space is added to the both edges and the axis is scaled to fit in the chart area.
position	AxisPosition - AxisPositionItem	Yes	Position of the axis.
reverse	boolean	Yes	Reverses order of tick labels.
singleStacked	boolean	-	If you might want to stack positive and negative values together.
stack	String	Yes	Sets the stack group. Axes at the same position with same stack are stacked.
stacked	boolean	Yes	If the axis are stacked.
stackWeight	double	Yes	Sets the weight of the scale in stack group. Used to determine the amount of allocated space for the scale within the group.
suggestedMax	double	Yes	Adjustment used when calculating the maximum data value.
suggestedMin	double	Yes	Adjustment used when calculating the minimum data value.
weight	double	Yes	The weight used to sort the axis. Higher weights are further away from the chart area.

Scriptable

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

All scriptable options callbacks will get a ScaleContext instance.

// creates a category axis 
CartesianLinearAxis axis = new CartesianLinearAxis(chart);
// sets the option by a callback 
axis.setBackgroundColor(new ColorCallback<ScaleContext>(){

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

The following options can be set by a callback:

Name	Callback	Returned types
alignToPixels	AlignToPixelsCallback	boolean
backgroundColor	ColorCallback<ScaleContext>	String - IsColor
beginAtZero	BeginAtZeroCallback	boolean
bounds	BoundsCallback	Bounds
display	DisplayCallback	boolean - Display
grace	GraceCallback	int - double
max	MinMaxCallback<Double>	double
min	MinMaxCallback<Double>	double
offset	ScaleOffsetCallback	boolean
position	ScalePositionCallback	AxisPosition - AxisPositionItem
reverse	ReverseCallback	boolean
stack	StackCallback	String
stacked	StackedCallback	boolean
stackWeight	ScaleWeightCallback	double
suggestedMax	MinMaxCallback<Double>	double
suggestedMin	MinMaxCallback<Double>	double
weight	ScaleWeightCallback	double

Ticks

The linear axis provides the following options for configuring tick marks.

// creates a linear axis 
CartesianLinearAxis axis = new CartesianLinearAxis(chart);
// sets and gets the max value
axis.getTicks().setColor(HtmlColor.RED);

IsColor color = axis.gteTicks().getColor();

The following are the attributes that you can set:

Name	Type	Scriptable	Description
align	TickAlign	-	The tick alignment along the axis.
autoSkip	boolean	-	If true, automatically calculates how many labels that can be shown and hides labels accordingly. Labels will be rotated up to maxRotation before skipping any. Turn autoSkip off to show all labels no matter what.
autoSkipPadding	int	-	The padding between the ticks on the horizontal axis when autoSkip is enabled.
backdropColor	String - IsColor	Yes	Color of label backdrops.
backdropPadding	Padding	-	The padding of tick backdrop. See padding documentation for more details.
color	String - IsColor	Yes	Color of ticks.
count	int	Yes	The number of ticks to generate. If specified, this overrides the automatic generation.
crossAlign	CrossAlign	-	The tick alignment perpendicular to the axis.
display	boolean	-	If true, the tick marks are shown.
font	IsFont	Yes	Font of ticks. See Font.
includeBounds	boolean	-	If true, the defined min and max values should be presented as ticks even if they are not "nice".
labelOffset	int	-	Distance in pixels to offset the label from the centre point of the tick (in the x-direction for the x-axis, and the y-direction for the y-axis). Note: This can cause labels at the edges to be cropped by the edge of the canvas.
maxRotation	int	-	The maximum rotation for tick labels when rotating to condense labels. Note: Rotation doesn't occur until necessary and only applicable to horizontal scales.
maxTicksLimit	int	Yes	Maximum number of ticks and gridlines to show.
minRotation	int	-	The minimum rotation for tick labels.
mirror	boolean	-	The flips tick labels around axis, displaying the labels inside the chart instead of outside. Note: Only applicable to vertical scales.
numberFormat	NumberFormatOptions	Yes	The number format options used by the default label formatter. See INTL number format documentation.
padding	int	-	The padding between the tick label and the axis.
precision	int	Yes	If defined and stepSize is not specified, the step size will be rounded to this many decimal places.
sampleSize	int	-	The number of ticks to examine when deciding how many labels will fit. Setting a smaller value will be faster, but may be less accurate when there is large variability in label length.
showLabelBackdrop	boolean	Yes	If true, draw a background behind the tick labels
stepSize	double	Yes	User defined fixed step size for the scale.
textStrokeColor	String - IsColor	Yes	The color of the stroke around the text.
textStrokeWidth	int	Yes	Stroke width around the text.
z	int	-	z-index of tick layer. Useful when ticks are drawn on chart area. Values less than or equals to 0 are drawn under data sets, greater than 0 on top.

Given the number of axis range settings, it is important to understand how they all interact with each other.

The suggestedMax and suggestedMin settings only change the data values that are used to scale the axis. These are useful for extending the range of the axis while maintaining the auto fit behavior.

In contrast to the suggested* settings, the min and max settings set explicit ends to the axes. When these are set, some data points may not be visible.

If stepSize set, the scale ticks will be enumerated by multiple of stepSize, having one tick per increment. If not set, the ticks are labeled automatically using the nice numbers algorithm.

The further customization of ticks, a callback is provided.

Ticks scriptable options

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

All scriptable options callbacks will get a ScaleContext instance.

// creates the axis for chart
CartesianLinearAxis axis = new CartesianLinearAxis(chart);
// sets the option by a callback 
axis.getTicks().setColor(new ColorCallback<ScaleContext>(){

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

The following options can be set by a callback:

Name	Callback	Returned types
backdropColor	ColorCallback<ScaleContext>	String - IsColor
color	ColorCallback<ScaleContext>	String - IsColor
count	CountCallback	int
font	FontCallback<ScaleContext>	FontItem
maxTicksLimit	MaxTicksLimitCallback	int
numberFormat	NumberFormatCallback	NumberFormatItem
precision	PrecisionCallback	int
showLabelBackdrop	ShowLabelBackdropCallback	boolean
stepSize	StepSizeCallback	double
textStrokeColor	ColorCallback<ScaleContext>	String - IsColor
textStrokeWidth	WidthCallback<ScaleContext>	int

Callback

It is also common to want to change the tick marks to include information about the data type. For example, adding a dollar sign ('$'). To do this, you need to implement a ticks callback in the axis configuration.

To apply a custom callback, you can set a TickCallback instance to the axis options, as following:

// creates the axis for chart
CartesianLinearAxis axis = new CartesianLinearAxis(chart);
// sets the option by a callback 
axis.getTicks().setCallback(new TickCallback(){

   /**
    * Changes the tick marks to include information about the data type.
    * 
    * @param axis axis instance where this callback as been defined
    * @param value value of tick
    * @param index index of tick
    * @param values list of all tick values
    * @return the tick to apply or if the callback returns null the associated grid line will be hidden.
    */
   public String onCallback(Axis axis, double value, int index, List<Double> values){
      // add $
      return "$" + value;
   }
         
});

See INTL number format documentation if you want to use a number formatter, provided out-of-the-box.

The callback can return a string (for single line) or a list of strings (for multiple lines).

NoSelectedDatasetTicksCallback callback

Charba provides a common implementation for tick callback to set the decimal digits of ticks in case of all data sets are hidden, to avoid the annoying standard format of doubles.

To apply the callback, you can set an instance to the axis options, as following:

// creates the axis for chart
CartesianLinearAxis axis = new CartesianLinearAxis(chart);
// sets the option by a callback 
axis.getTicks().setCallback(new NoSelectedDatasetTicksCallback());

The default decimal precision is 2. A custom precision can be set by the constructor of callback, as following:

// creates the axis for chart
CartesianLinearAxis axis = new CartesianLinearAxis(chart);
// sets the option by a callback 
// 3 decimal digits 
axis.getTicks().setCallback(new NoSelectedDatasetTicksCallback(3));