# 新坐标轴
¥New Axes
Chart.js 中的轴可以单独扩展。轴应始终从 Chart.Scale
派生,但这不是强制性要求。
¥Axes in Chart.js can be individually extended. Axes should always derive from Chart.Scale
but this is not a mandatory requirement.
class MyScale extends Chart.Scale {
/* extensions ... */
}
MyScale.id = 'myScale';
MyScale.defaults = defaultConfigObject;
// MyScale is now derived from Chart.Scale
创建刻度类后,你需要将其注册到全局图表对象以便使用。
¥Once you have created your scale class, you need to register it with the global chart object so that it can be used.
Chart.register(MyScale);
// If the new scale is not extending Chart.Scale, the prototype can not be used to detect what
// you are trying to register - so you need to be explicit:
// Chart.registry.addScales(MyScale);
要使用新比例,只需在创建图表时将字符串键传递给配置即可。
¥To use the new scale, simply pass in the string key to the config when creating a chart.
const lineChart = new Chart(ctx, {
data: data,
type: 'line',
options: {
scales: {
y: {
type: 'myScale' // this is the same id that was set on the scale
}
}
}
});
# 标尺属性
¥Scale Properties
在拟合过程中,缩放实例被赋予以下属性。
¥Scale instances are given the following properties during the fitting process.
{
left: number, // left edge of the scale bounding box
right: number, // right edge of the bounding box
top: number,
bottom: number,
width: number, // the same as right - left
height: number, // the same as bottom - top
// Margin on each side. Like css, this is outside the bounding box.
margins: {
left: number,
right: number,
top: number,
bottom: number
},
// Amount of padding on the inside of the bounding box (like CSS)
paddingLeft: number,
paddingRight: number,
paddingTop: number,
paddingBottom: number
}
# 标尺接口
¥Scale Interface
要使用 Chart.js,自定义刻度类型必须实现以下接口。
¥To work with Chart.js, custom scale types must implement the following interface.
{
// Determines the data limits. Should set this.min and this.max to be the data max/min
determineDataLimits: function() {},
// Generate tick marks. this.chart is the chart instance. The data object can be accessed as this.chart.data
// buildTicks() should create a ticks array on the axis instance, if you intend to use any of the implementations from the base class
buildTicks: function() {},
// Get the label to show for the given value
getLabelForValue: function(value) {},
// Get the pixel (x coordinate for horizontal axis, y coordinate for vertical axis) for a given value
// @param index: index into the ticks array
getPixelForTick: function(index) {},
// Get the pixel (x coordinate for horizontal axis, y coordinate for vertical axis) for a given value
// @param value : the value to get the pixel for
// @param [index] : index into the data array of the value
getPixelForValue: function(value, index) {},
// Get the value for a given pixel (x coordinate for horizontal axis, y coordinate for vertical axis)
// @param pixel : pixel value
getValueForPixel: function(pixel) {}
}
可选地,以下方法也可能被覆盖,但是 Chart.Scale
基类已经提供了一个实现。
¥Optionally, the following methods may also be overwritten, but an implementation is already provided by the Chart.Scale
base class.
{
// Adds labels to objects in the ticks array. The default implementation simply calls this.options.ticks.callback(numericalTick, index, ticks);
generateTickLabels: function() {},
// Determine how much the labels will rotate by. The default implementation will only rotate labels if the scale is horizontal.
calculateLabelRotation: function() {},
// Fits the scale into the canvas.
// this.maxWidth and this.maxHeight will tell you the maximum dimensions the scale instance can be. Scales should endeavour to be as efficient as possible with canvas space.
// this.margins is the amount of space you have on either side of your scale that you may expand in to. This is used already for calculating the best label rotation
// You must set this.minSize to be the size of your scale. It must be an object containing 2 properties: width and height.
// You must set this.width to be the width and this.height to be the height of the scale
fit: function() {},
// Draws the scale onto the canvas. this.(left|right|top|bottom) will have been populated to tell you the area on the canvas to draw in
// @param chartArea : an object containing four properties: left, right, top, bottom. This is the rectangle that lines, bars, etc will be drawn in. It may be used, for example, to draw grid lines.
draw: function(chartArea) {}
}
Core.Scale 基类还有一些你可能会觉得有用的实用函数。
¥The Core.Scale base class also has some utility functions that you may find useful.
{
// Returns true if the scale instance is horizontal
isHorizontal: function() {},
// Returns the scale tick objects ({label, major})
getTicks: function() {}
}