opentk/opentk — pull request #134 by thefiddler (2014-06-10 14:13:03+00:00)
Title: [X11] Match win32 wheel coordinate system

OpenTK uses the win32 wheel coordinate system, where
(+h, +v) = (right, up). XI2 uses (+h, +v) = (right, down)
instead, so we need to flip the vertical offset.

Fixes issue #133 and https://github.com/mono/MonoGame/issues/2686