Comment 6 for bug 1738676

SCROLLED WINDOWS AND NATURAL SCROLLING
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For scrolled windows, the input from the track-pad reverses...

  With natural scrolling DISABLED:
  - Sliding fingers down on a track-pad, slides the view down
  - Sliding fingers up on a track-pad, slides the view up

  And with natural scrolling ENABLED:
  - Sliding fingers down on a track-pad, slides the view up
  - Sliding fingers up on a track-pad, slides the view down

"Flipping" the behavior of a scrolled window based on whether or not natural scrolling is set, makes a lot of sense. That is how it should work.

VOLUME CONTROL AND NATURAL SCROLLING
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However, "flipping" the behavior of a volume control, based on whether or not natural scrolling is set, *does not* make sense. Volume should always go up, when you slide up. Volume should always go down, when you slide down.

For volume control, the input from the track-pad should NOT reverse...

  With natural scrolling DISABLED:
  - Sliding fingers down on a track-pad, should cause volume to decrease
  - Sliding fingers up on a track-pad, should cause volume to increase

  With natural scrolling ENABLED:
  - Sliding fingers down on a track-pad, should STILL cause volume to decrease
  - Sliding fingers up on a track-pad, should STILL cause volume to increase

PROPOSED SOLUTION
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In order to resolve this issue, I think we can apply the following rule:

  If
    org.gnome.desktop.peripherals.touchpad natural-scroll = true

  Then
    GtkVolumeButton widget should reverse the scroll event input

Essentially, the widget itself would undo the "flip" caused by setting natural-scrolling. Of course, if natural scrolling isn't set, the widget would behave as it normally does.