Panning Broken with Chart.js 2.9.0

[exwm]

With the latest chart.js v2.9.0 the scale.getValueForPixel method has been changed and its use in chartjs-plugin-zoom (tested with v0.7.4) causes misbehavior of pan with numerical scales and possibly others. Specifically, panning causes the chart to zoom. Exactly one of either the start or end of the scale remains fixed while the other stretches outwards.

The panNumericalScale function in chartjs-plugin-zoom uses scale.getValueForPixel to get the new minimum and maximum values for the scale (see

chartjs-plugin-zoom/src/plugin.js

Line 257 in 1cf272f

var newMin = scale.getValueForPixel(scale.getPixelForValue(prevStart) - delta);

).

I believe the changes that are causing this issue were made in this commit of chart.js: chartjs/Chart.js@cbace1c#diff-f0d8f86fecab28f396793911b0e9f36dR746.

A demonstration of the bug can be found here: https://codepen.io/exwm/pen/vYYZREw. Simply pan the chart by dragging with the mouse.

[benmccann]

FYI @kurkle. Maybe a bug in handling reverse support in core.scale

[etimberg]

Chart.js v2.9.1 has been released with a fix for this issue