Set the new position of the fill level indicator.
The “fill level” is probably best described by its most prominent use case, which is an indicator for the amount of pre-buffering in a streaming media player. In that use case, the value of the range would indicate the current play position, and the fill level would be the position up to which the file/stream has been downloaded.
This amount of prebuffering can be displayed on the range’s trough
and is themeable separately from the trough. To enable fill level
gtk_range_set_show_fill_level(). The range defaults
to not showing the fill level.
Additionally, it’s possible to restrict the range’s slider position
to values which are smaller than the fill level. This is controlled
gtk_range_set_restrict_to_fill_level() and is by default enabled.