default
The direction of the light source used to generate the hillshading with 0 as the top of the viewport if hillshade-illumination-anchor is set to viewport and due north if hillshade-illumination-anchor is set to map and no 3d lights enabled. If hillshade-illumination-anchor is set to map and 3d lights enabled, the direction from 3d lights is used instead.
This is an Expression representation of "hillshade-illumination-direction".