[MACOS] Trackpad scrolling conflicts with scroll animations when smooth scrolling is enabled

[wriver0s]

If you have smooth scrolling enabled (the "Disable scroll animations" option unchecked) and try to scroll through an image using a Mac trackpad, the image fights back. It feels like it wants to snap back to where it was instead of following the gesture.

Disabling smooth scrolling fixes it, but that's not ideal.

The trackpad handler (wheelEventTrackpad) applies scroll deltas directly to the scrollbar, but it doesn't check if there's already a scroll animation running. So you end up with the animation trying to move the scrollbar one way while your trackpad input tries to move it another way. They fight each other.

Maybe just stop any running animations before applying the trackpad input?

 void Viewer::wheelEventTrackpad(QWheelEvent *event)                                                                                        
   {
      auto delta = event->pixelDelta();

      // Stop any running scroll animations to prevent conflict with trackpad input
      if (verticalScroller->state() == QAbstractAnimation::Running) {
          verticalScroller->stop();
      }
      if (horizontalScroller->state() == QAbstractAnimation::Running) {
          horizontalScroller->stop();
      }

      // ... rest unchanged

YACReader/viewer.cpp

[luisangelsm]

Disabling smooth scrolling when using hdpi scrolling is not that bad in terms of UX, but the solution is implement proper kinetic scrolling.

The challenge is to have logic that works well with mouse wheel and trackpads (where the user actually expects momentum when scrolling).

But if you find a way to make it even sightly better feel free to open a PR.