fix: trigger onZoom from zoomScale

[kurkle]

fix #775

[github-actions]

Size Change: +12 B (+0.06%)

Total Size: 20.5 kB

Filename	Size	Change
dist/chartjs-plugin-zoom.esm.js	7.44 kB	+2 B (+0.03%)
dist/chartjs-plugin-zoom.js	7.58 kB	+4 B (+0.05%)
dist/chartjs-plugin-zoom.min.js	5.51 kB	+6 B (+0.11%)

_{compressed-size-action}

[yubiuser]

This update broke our use case and I don't know how to mitigate the new behavior. We basically have the same situation as described as in #768:

We have a time series bar chart with only positive y-values. When zooming, y-axis should stay fixed at zero, because it does not make sense to lose the zero anchor. We basically used onZoom to trigger chart.zoomScale to set the new scale with fixed y min to zero.

But with this change, this causes an endless loop. Any idea how to circumvent this?

Old code

      onZoom: function ({ chart }) {
        // The first time the chart is zoomed, save the maximum initial scale bound
        if (!chart.absMax) chart.absMax = chart.getInitialScaleBounds().y.max;
        // Calculate the maximum value to be shown for the current zoom level
        const zoomMax = chart.absMax / chart.getZoomLevel();
        // Update the y axis scale
        chart.zoomScale("y", { min: 0, max: zoomMax }, "default");
        // Update the y axis ticks and round values to natural numbers
        chart.options.scales.y.ticks.callback = function (value) {
          return value.toFixed(0);
        };

[kurkle]

Instead of calling zoomScale from onZoom, just specify min: 0 in the y-scale options?

Or, you can just update the scale directly:

chart.options.scales.y.min = 0;
chart.options.scales.y.max = chart.absMax / chart.getZoomLevel(); // probably not needed
chart.update();

[yubiuser]

Instead of calling zoomScale from onZoom, just specify min: 0 in the y-scale options?

This does not work, as it specifies the minimum, but not the maximal minimum (it doesn't get negative).

---

chart.options.scales.y.min = 0;
chart.options.scales.y.max = chart.absMax / chart.getZoomLevel(); // probably not needed
chart.update();

This works, but gives an unpleasant scale jump

Before it was smooth

[kurkle]

maybe chart.update('none') produces similar result?

[yubiuser]

Yes, but now I can only zoom in, and not zoom out again.

      onZoom: function ({ chart }) {
        chart.options.scales.y.min = 0;
        chart.update('none');
        }

[kurkle]

I've created #901 for letting you do something like:

      onZoom: function ({ chart, trigger }) {
        if (trigger === 'api') {
          // Ignore onZoom triggered by the chart.zoomScale api call below
          return;
        }
        // The first time the chart is zoomed, save the maximum initial scale bound
        if (!chart.absMax) chart.absMax = chart.getInitialScaleBounds().y.max;
        // Calculate the maximum value to be shown for the current zoom level
        const zoomMax = chart.absMax / chart.getZoomLevel();
        // Update the y axis scale
        chart.zoomScale("y", { min: 0, max: zoomMax }, "default");
        // Update the y axis ticks and round values to natural numbers
        chart.options.scales.y.ticks.callback = function (value) {
          return value.toFixed(0);
        };

[yubiuser]

Perfect. Tested it locally compiled and it works like charm.