Add "natural" scrolling support for trackpads

[tresf]

Adds QWheelEvent::inverted() support to LcdSpinbox, Knob.

Closes #5507

If desired, may be a candidate for backport to 1.2.0 with a cherry-pick.

Edit: On second thought, let's let 1.2.x drift into the archives of time. master master race. :D

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Linux

• Linux (AppImage): lmms-1.2.1.681-linux-x86_64.AppImage (build link)

Windows

• Windows 32-bit: lmms-1.2.1.681-mingw-win32.exe (build link)
• Windows 64-bit: lmms-1.2.1.681-mingw-win64.exe (build link)
• Windows 32-bit: lmms-1.2.1-msvc2017-win32.exe (build link)
• Windows 64-bit: lmms-1.2.1-msvc2017-win64.exe (build link)

macOS

• macOS : lmms-1.2.1.681-mac10.13.dmg (build link)

🤖

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[zonkmachine]

LGTM. This looks fine for 1.2.2

[PhysSong]

FYI, you will find some more places if you git grep for delta().

[tresf]

FYI, you will find some more places if you git grep for delta().

Thanks. Can we work from an exhaustive list then? (PLEASE EDIT!)

File	Needs Flip	Done
src/gui/editors/AutomationEditor.cpp	✅(excluding horizontal scroll)	🚫 Not sure where 🤦
src/gui/editors/PianoRoll.cpp	✅(note panning)	✅
src/gui/editors/SongEditor.cpp	✅(excluding horizontal scroll)	✅
src/gui/widgets/ComboBox.cpp	✅	✅
vsrc/gui/widgets/Fader.cpp	✅	✅
src/gui/widgets/Knob.cpp	✅	✅
src/gui/widgets/LcdSpinBox.cpp	✅	✅
src/gui/widgets/TabWidget.cpp	✖️(no, but could use proper card-swipe support)	🚫 Works as-is, but too sensitive and no left/right scroll support
src/tracks/Pattern.cpp	✅(Velocity for beat/bassline editor)	✅ It's not in Pattern.cpp, but tackled in MidiClipView .

I'm not sure about where the delta() is used for some of the editors. If it's scrubbing/scroll bars, that's behaving properly, but I notices that note panning on Piano Roll needs it so I might be missing something.

Need to work on more places

[JohannesLorenz]

@tresf Merging this already (I think you can merge in CLI and still keep the PR open) might reduce merge conflicts after reorg. It's also useful to have it working for the most important widgets, so maybe get this code to master?

[tresf]

@tresf Merging this already (I think you can merge in CLI and still keep the PR open) might reduce merge conflicts after reorg. It's also useful to have it working for the most important widgets, so maybe get this code to master?

The code will be trivial to rebase. @PhysSong's instincts were to do this one for most items and I don't hate that idea. I'll move it to a WIP PR because it will require work before its ready.

[tresf]

Table updated #5510 (comment). Ready for review.

[Rossmaxx]

The minimum qt version is now 5.9 so this check is obsolete now.

[tresf]

The minimum qt version is now 5.9 so this check is obsolete now.

Removed checks.