incorrect interpolation for transitions on hillshade-illumination-direction

[stevage]

mapbox-gl-js version: 0.43.0

Steps to Trigger Behavior

1. Create a hilshade layer with hillshade-illumination-direction of 359
2. Call map.setPaintProperty(layername, 'hillshade-illumination-direction', 0)

Expected Behavior

Almost no visible effect.

Actual Behavior

Entire map repaints with large visible flicker.

Easily seen here: https://bl.ocks.org/stevage/raw/a4569595d8592181ab09a5a13166be8d

(The current direction is shown in the URL)

Code: https://gist.github.com/stevage/a4569595d8592181ab09a5a13166be8d

[mollymerp]

yes I see what you mean – I don't think it's triggering a page refresh though, its just transitioning from 359 -> 0 counterclockwise so the light source does almost a full rotation instead of just moving slightly clockwise to 360/0.

A workaround right now is to set transition.duration to 0 https://www.mapbox.com/mapbox-gl-js/style-spec#root-transition

[stevage]

Ah, that seems so obvious now :) Thanks.