Using the scrollwheel to zoom.

[mtetreault]

From what I see from the code base there is currently no ways to use the scrollwheel to zoom.

Is this a feature that is planned to be released? If not, how would you implement such a feature?

Thanks

[danmana]

While the plugin does not support scrolling with the mouse wheel, it is possible to implement it. All you need is to call the plugins doZoom method

const chart = new Chart(...);
const plugin = Chart.plugins.getAll().find((p) => p.id === "crosshair");
plugin.doZoom(chart, myZoomStart, myZoomEnd);

Here is a simple version that zooms by 10% https://codepen.io/danmana/pen/GRZQNpR?editors=1010 You might want to implement a smarter way to calculate myZoomStart/End that takes into account the current mouse position (see center variable below)

canvas.addEventListener("wheel", (event) => {
  const delta = event.deltaY;
  const xscale = chart.scales['x-axis-0'];
  const start = chart.crosshair.start === undefined ? xscale.min : chart.crosshair.start;
  const end = chart.crosshair.end === undefined ? xscale.max : chart.crosshair.end;
  const ZOOM_FACTOR = 0.1; // 10%
  const increment = Math.sign(delta) * Math.abs(end - start) * ZOOM_FACTOR / 2;
  
  // might want to use chart.crosshair.x and center to zoom around the current mouse position
  const center = xscale.getValueForPixel(chart.crosshair.x);
    
  const myZoomStart = start + increment;
  const myZoomEnd = end - increment;
  
  console.log(delta, start, end, center, increment, myZoomStart, myZoomEnd);
  
  plugin.doZoom(
    chart,
    myZoomStart,
    myZoomEnd
  );
});

[anko20094]

const plugin = Chart.plugins.getAll().find((p) => p.id === "crosshair");

How should code been rewriting for versions 3.x.x?

[danmana]

Chart.js 3.x.x update

Obtaining the plugin is a bit easier now:

const plugin = Chart.registry.getPlugin('crosshair');

Note: there were some changes in Chart.js v3 regarding scales. Besides that, the code above is unchanged.

const xscale = chart.scales['x'];

See example: https://codepen.io/danmana/pen/QWQjVZb?editors=1010