Time Chart

An chart library specialized for large-scale time-series data, built on WebGL.

Flexable. Realtime monitor. High performance interaction.

Live Demo

Performance

Taking advantage of the newest WebGL technology, we can directly talk to GPU, pushing the limit of the performance of rendering chart in browser. This library can display almost unlimited data points, and handle user interactions (pan / zoom) at 60 fps.

We compare the performance of this library and some other popular libraries. See Performance

Usage

Installation

• Use npm

  npm install timechart

• Use HTML script tag

  This library depends on D3 to draw axes and something else. It needs to be included seperatedly.

  <script src="https://cdn.jsdelivr.net/npm/d3-array@3"></script>
  <script src="https://cdn.jsdelivr.net/npm/d3-color@3"></script>
  <script src="https://cdn.jsdelivr.net/npm/d3-format@3"></script>
  <script src="https://cdn.jsdelivr.net/npm/d3-interpolate@3"></script>
  <script src="https://cdn.jsdelivr.net/npm/d3-time@3"></script>
  <script src="https://cdn.jsdelivr.net/npm/d3-time-format@4"></script>
  <script src="https://cdn.jsdelivr.net/npm/d3-scale@4"></script>
  <script src="https://cdn.jsdelivr.net/npm/d3-selection@3"></script>
  <script src="https://cdn.jsdelivr.net/npm/d3-axis@3"></script>
  <script src="https://huww98.github.io/TimeChart/dist/timechart.min.js"></script>

Basic

Display a basic line chart with axes.

<div id="chart" style="width: 100%; height: 640px;"></div>

const el = document.getElementById('chart');
const data = [];
for (let x = 0; x < 100; x++) {
    data.push({x, y: Math.random()});
}
const chart = new TimeChart(el, {
    series: [{ data }],
});

Live

Assemble Your Own Chart

New in v1.

TimeChart comes with a modular design. Almost all functions are implemented as plugins. You can pick the plugins you need, so that you don't pay for functions you don't use.

Offical plugins:

• lineChart: draw the line chart with WebGL, the biggest selling point of this library.
• d3Axis: intergret with d3-axis to draw the axes.
• legend: show a legend at top-right.
• crosshair: show crosshair under the mouse.
• nearestPoint: highlight the data points in each series that is nearest to the mouse.
• chartZoom: respond to mouse, keyboard, touch event to zoom/pan the chart. See also the interaction method

As an example, to assemble your own chart with all offical plugins added:

import TimeChart from 'timechart/core';
import { lineChart } from 'timechart/plugins/lineChart';
import { d3Axis } from 'timechart/plugins/d3Axis';
import { legend } from 'timechart/plugins/legend';
import { crosshair } from 'timechart/plugins/crosshair';
import { nearestPoint } from 'timechart/plugins/nearestPoint';
import { TimeChartZoomPlugin } from 'timechart/plugins/chartZoom';

const el = document.getElementById('chart');
const chart = new TimeChart(el, {
    data: {...},
    plugins: {
        lineChart,
        d3Axis,
        legend,
        crosshair,
        nearestPoint,
        zoom: new TimeChartZoomPlugin({...}),
        tooltip: new TimeChartTooltipPlugin({...}),
    }
});

This is almost equivalent to just import TimeChart from 'timechart';, except:

• The zoom options are now passed directly to TimeChartZoomPlugin.
• To change the zoom options dynamically, use chart.plugins.zoom.options instead of original chart.options.zoom.

You can also write your own plugins. Read the guide.

For users who use HTML script tag to import TimeChart, use this instead:

<!-- D3 scripts -->
<script src="https://huww98.github.io/TimeChart/dist/timechart.min.js"></script>
<script>
    const el = document.getElementById('chart');
    const chart = new TimeChart.core(el, {
        data: {...},
        plugins: {
            lineChart: TimeChart.plugins.lineChart,
            ...
        }
    });
</script>

Demo

Dynamic Data

To add/remove data dynamically, just change the data array with conventional array prototype methods, then call chart.update().

Some restrictions to the data manipulations:

• The prototype of data array will be overridden. The length of this array can only be modified with the following overrode array prototype method: push, pop, shift, unshift, splice. The behavior is undefined if the length of the array is changed by any other means.
• Once you call update, the data will be synchronized to GPU. Then these data cannot be modified, and can only be deleted from both ends. Illegal modification by the overrode splice prototype method will lead to an exception. Other Illegal modifications will lead to undefined behavior.
• Any data that has not been synchronized to GPU can be modified at will.

  const data = [...];  // Assume it contains 10 data points
  const chart = new TimeChart(el, {
      series: [{ data }],
  });
  data.push({x, y}, {x, y}, {x, y});  // OK
  data.splice(-2, 1);  // OK, data not synced yet
  chart.update();
  
  data.splice(-2, 1);  // RangeError
  data.splice(-2, 2);  // OK, delete the last two data points
  data.pop();          // OK, delete the last data point
  data.splice(0, 2);   // OK, delete the first two data points
  chart.update();      // See data deleted
  
  Array.prototype.pop.call(data)  // Wrong. Only the overridden methods should be used
  data.length = 3;     // Wrong. Changes cannot be tracked
  data[3] = {x, y};    // Wrong unless data[3] is already in array and not synced to GPU

• The x value of each data point must be monotonically increasing.
• Due to the limitation of single-precision floating-point numbers, if the absolute value of x is large (e.g. Date.now()), you may need to use baseTime option (see below) to make the chart render properly.

  let startTime = Date.now(); // Set the start time e.g.   1626186924936
  
  let bar = []; // holds the series data
  
  // build the chart
  const chart = new TimeChart(el, {
      series: [{
          name: 'foo',
          data: bar
      }],
      baseTime: startTime,
  });
  
  // update data
  bar.push({x: 1, y: 10}); // 1ms after start time
  bar.push({x: 43, y: 6.04}); // 43ms after start time
  bar.push({x: 89, y: 3.95}); // 89ms after start time
  
  // update chart
  chart.update();

Global Options

Specify these options in top level option object. e.g. to specify lineWidth:

const chart = new TimeChart(el, {
    series: [{ data }],
    lineWidth: 10,
});

• lineWidth (number): default line width for every data series.

  default: 1

• backgroundColor (CSS color specifier or d3-color instance)

  default: 'transparent'

• color (CSS color specifier or d3-color instance): line color

  default: color CSS property value at initialization.

• paddingTop / paddingRight / paddingLeft / paddingBottom (number): Padding to add to chart area in CSS pixel. Also reserve space for axes.

  default: 10 / 10 / 45 / 20

• renderPaddingTop / renderPaddingRight / renderPaddingLeft / renderPaddingBottom (number): Like the padding* counterpart, but for WebGL rendering canvas.

  default: 0

• xRange / yRange ({min: number, max: number} or 'auto'): The range of x / y axes. Also use this to control pan / zoom programmatically. Specify 'auto' to calculate these range from data automatically. Data points outside these range will be drawn in padding area, to display as much data as possible to user.

  default: 'auto'

• realTime (boolean): If true, move xRange to newest data point at every frame.

  default: false

• baseTime (number): Milliseconds since new Date(0). Every x in data are relative to this. Set this option and keep the absolute value of x small for higher floating point precision.

  default: 0

• xScaleType (() => Scale): A factory method that returns an object conforming d3-scale interface. Can be used to customize the appearance of x-axis. scaleTime, scaleUtc, scaleLinear from d3-scale are known to work.

  default: d3.scaleTime

• debugWebGL (boolean): If true, detect any error in WebGL calls. Most WebGL calls are asynchronized, and detecting error will force synchronization, which may slows down the program. Mainly used in development of this library.

  default: false

• legend (boolean): If true, show the legend.

  default: true

Series Options

Specify these options in series option object. e.g. to specify lineWidth:

const chart = new TimeChart(el, {
    series: [{
        data,
        lineWidth: 10,
    }],
});

• data ({x: number, y: number}[]): Array of data points to be drawn. x is the time elapsed in millisecond since baseTime

• lineWidth (number or undefined): If undefined, use global option.

  default: undefined

• lineType (number): Take one of the following:

  • LineType.Line: straight lines connecting data points
  • LineType.Step: step function, only horizontal and vertical lines
  • LineType.NativeLine: like LineType.Line, but use native WebGL line drawing capability. This is faster than LineType.Line, but the line width is fixed at 1 pixel on most devices.
  • LineType.NativePoint: draw points at each data point using native WebGL point drawing capability. lineWidth is reused to specify point size in this case.

  default: LineType.Line

• stepLocation (number): Only effective if lineType === LineType.Step. Where to draw the vertical line. Specified as a ratio of the distance between two adjacent data points. Usually in the range of [0, 1].

  default: 0.5

• name (string): The name of the series. Will be shown in legend and tooltips.

  default: ''

• color (CSS color specifier or d3-color instance or undefined): line color. If undefined, use global option.

  default: undefined

• visible (boolean): Whether this series is visible

  default: true

Zoom Options

These options enable the builtin touch / mouse / trackpad interaction support. The x, y axis can be enabled separately.

Specify these options in zoom option object. e.g. to specify autoRange:

const chart = new TimeChart(el, {
    series: [{ data }],
    zoom: {
        x: {
            autoRange: true,
        },
        y: {
            autoRange: true,
        }
    }
});

New in v1. If you are using the plugins, pass these options to the TimeChartZoomPlugin plugin.

import TimeChart from 'timechart/core';
import { TimeChartZoomPlugin } from 'timechart/plugins/chartZoom';
const chart = new TimeChart(el, {
    series: [{ data }],
    plugins: {
        zoom: new TimeChartZoomPlugin({x: {autoRange: true}})
    },
});

Then old chart.options.chart is not available. Use chart.plugins.zoom.options instead.

• panMouseButtons (number): allowed mouth buttons to trigger panning. see MouseEvent.buttons

  default: 1 | 2 | 4

• touchMinPoints (number): minimum number of touch points needed for the chart to respond to the gesture. Useful if you want to reserve some gesture for other plugins (e.g. selectZoom).

  default: 1

• autoRange (boolean): Per axis. Determine maxDomain, minDomain automatically.

  default: false

• maxDomain / minDomain (number): Per axis. The limit of xRange / yRange

  default: Infinity / -Infinity

• maxDomainExtent / minDomainExtent (number): Per axis. The limit of max - min in xRange / yRange

  default: Infinity / 0

Tooltip Options

const chart = new TimeChart({
    ...,
    tooltip: { enabled: true }
})

Or

import TimeChart from 'timechart/core';
import { TimeChartTooltipPlugin } from 'timechart/plugins/tooltip';
const chart = new TimeChart(el, {
    ...,
    plugins: {
        tooltip: new TimeChartTooltipPlugin({ enabled: true, xLabel: 'Time' })
    },
});

• enabled (boolean): Whether to enable the tooltip on hover

  default: false

• xLabel (string): Label for the X axis in the tooltip

  default: "X"

• xFormatter ((number) => string): Function to format the X axis value in the tooltip

  default: x => x.toLocaleString()

Methods

• chart.update(): Request update after some options have been changed. You can call this as many times as needed. The actual update will only happen once per frame.

• chart.dispose(): Dispose all the resources used by this chart instance. Note: We use shadow root to protect the chart from unintended style conflict. However, there is no easy way to remove the shadow root after dispose. But you can reuse the same HTML element to create another TimeChart. Example

• chart.onResize(): Calculate size after layout changes. This method is automatically called when window size changed. However, if there are some layout changes that TimeChart is unaware of, you need to call this method manually.

Interaction

With touch screen:

• 1 finger to pan
• 2 or more finger to pan and zoom

With mouse:

• Left button drag to pan
• wheel scroll translate X axis
• Alt + wheel scroll to translate Y axis
• Ctrl + wheel scroll to zoom X axis
• Ctrl + Alt + wheel scroll to zoom Y axis
• Hold Shift key to speed up translate or zoom 5 times

With trackpad:

• Pan X or Y direction to translate X axis
• Alt + Pan X/Y direction to translate X/Y axis
• Pinch to zoom X axis
• Alt + pinch to zoom Y axis
• Hold Shift key to speed up translate or zoom 5 times

Styling

The chart is in a shadow root so that most CSS in the main document can not affect it. But we do provide some styling interface.

For example, we can support dark theme easily:

<div id="chart" class="dark-theme"></div>

.dark-theme {
    color: white;
    background: black;
    --background-overlay: black;
}

Live

The --background-overlay CSS property is used in some non-transparent element on top on the chart.

The background of the chart is transparent by default. So it's easy to change the background by setting the background of parent element.

All foreground elements will change color to match the color CSS property. However, chart is drawn in canvas and cannot respond to CSS property changes. You need to change the color manually if you want to change the color after initialiation.

Development

• run npm install to install dependencies
• run npm start to automatically build changes
• run npm run demo then open http://127.0.0.1:8080/demo/index.html to test changes
• run npm test to run automatic tests