icon size jump using a nested data expression in a zoom expression

[tristen]

mapbox-gl-js version: v1.4.0
browser: Google Chrome Version 77.0.3865.120 (Official Build) (64-bit)

Steps to Trigger Behavior

Create a zoom expression for the icon-size property with a data condition within it. i.e.

[
  'interpolate',
  ['exponential', 1.5],
  ['zoom'],
  8,
  ['match', ['get', 'iso_3166_1'], ['JP'], 0.75, 1],
  14,
  1
]

Link to Demonstration

The bug looks like this:

The test case I have for this is pretty subtle and doesn't totally match the gif above. It's possible the addition of collision detection where there are more features on the map is causing it? https://jsfiddle.net/tristen/zn7ks40L/

Expected Behavior

There would be no jump in size but that the size of the icon would interpolate across the zoom expression set.

Actual Behavior

Icon jumps down in size when zooming from one zoom stop to another.

[arindam1993]

I think this could have potentially fixed this.
https://github.com/mapbox/mapbox-gl-js/pull/8818/files

@ansis what do you think?

[chloekraw]

The effect of this behavior on the jsfiddle is pretty subtle, but I forked it to use v1.5.0-beta.1 which contains #8818 and the behavior when moving across zoom levels appears to be the same: https://jsfiddle.net/k1ymzr79/.

I also wonder if the problem is not in the interpolation of icon-size but that text-size isn't zoom-interpolated with comparable logic, so that at lower zooms, the text is too big for the icon and makes the icon size appear incorrect in relation.

@tristen what do you think?

[tristen]

I also wonder if the problem is not in the interpolation of icon-size but that text-size isn't zoom-interpolated with comparable logic, so that at lower zooms, the text is too big for the icon and makes the icon size appear incorrect in relation.

@chloekraw even with the same comparable logic for text-size the icon itself jumps down considerably in size.

[ansis]

This is a tricky case because the icon is affected both by text-size (because of icon-text-fit) and icon-size.

Do you want both the text and icon to scale smoothly to a smaller size? Or just the icon?

[tristen]

Hmm @ansis that particular example doesn't use icon-text-fit. the icon is a fixed width.