Zoom is unstable at zoom limits

[TheophileMot]

When zooming in and out, I expect the timeline to remain centred on the same point; for example, if I zoom in a few steps using the mouse wheel, then zoom back out a few steps, I should be back where I started.

However, when the zoom hits the zoomMax or zoomMin limit, the timeline will noticeably shift. This means that after repeatedly zooming in and out, the timeline will drift off to one side or the other.

To reproduce: go to this zoom limit demo from the documentation and zoom in or out all the way repeatedly. (The bug is most apparent when the cursor is near the beginning or end of the timeline.)

In the clip below, the cursor doesn't move; therefore we expect that the two items should always be in the same place after zooming in and out again.

[TheophileMot]

For anyone who may happen to stumble across this issue in the future: the problem is in Range.js in the function _applyRange. When zoomMax is exceeded, the new range is calculated as follows:

  diff = ((newEnd - newStart) - zoomMax);
  newStart += diff / 2;
  newEnd -= diff / 2;

This is wrong, as it disregards the fixed point at the cursor. Instead:

  const fixedPt = (newStart * this.end - this.start * newEnd) / ((this.end - this.start) - (newEnd - newStart));
  newStart = zoomMax * (fixedPt - this.start) / (this.start - this.end) + fixedPt;
  newEnd = newStart + zoomMax;

(And similarly for zoomMin.)

[ajaz-rehman]

Thanks, @TheophileMot but how do I change this?

[TheophileMot]

@fateslayer Unfortunately, it seems that this project is dead; it hasn't been updated in about a year.

I ended up cloning the repo to change the lines of code in question, then building it locally.

[ajaz-rehman]

Thanks for responding @TheophileMot. I guess I'll have to do the same.