func allows you to change how the scale value is displayed.
The given function will return an allocated string representing value. That string will then be used to display the scale's
value.
If NULL is passed as func, the value will be displayed on its own, rounded according to the value of the [
property@GtkScale:digits] property.
| this |
a `GtkScale` |
| func |
function that formats the value |
| destroy_notify |
destroy function for |
| user_data |
user data to pass to |