Specifies the unit of scroll deltas.
When you get
GDK_SCROLL_UNIT_WHEEL, a delta of 1.0 means 1 wheel detent
click in the south direction, 2.0 means 2 wheel detent clicks in the south
direction… This is the same logic for negative values but in the north direction.
If you get
GDK_SCROLL_UNIT_SURFACE, are managing a scrollable view and get a
value of 123, you have to scroll 123 surface logical pixels right if it’s
delta_x or down if it’s
delta_y. This is the same logic for negative values
but you have to scroll left instead of right if it’s
delta_x and up instead
of down if it’s
1 surface logical pixel is equal to 1 real screen pixel multiplied by the final scale factor of your graphical interface (the product of the desktop scale factor and eventually a custom scale factor in your app).