If #GtkScale:has-origin is set to %TRUE (the default), the scale will highlight the part of the trough between the origin (bottom or left side) and the current value.
%TRUE if the scale has an origin
3.4
See Implementation
If #GtkScale:has-origin is set to %TRUE (the default), the scale will highlight the part of the trough between the origin (bottom or left side) and the current value.