Fix regressions from QScroller patches

(Taken from BoF notes from mailing list thread “Okular BoF for Akademy”)

QScroller patches

Introduced in 20.04 releases, they improve a bit some use causes but are causing serious regressions including crashes in other cases. MR: !50 (merged)

We will produce a list of bugs that we want fixed before 22 October. If they are fixed or making good progress before then, we keep the scrolling change in. Otherwise, we revert. Nate to triage bugs and identify ones to fix:

Fix or make good progress on fixing these regressions before 22 October:

• PgUp/PgDn smooth scroll animation needs to finish before hitting the key again works
  • https://bugs.kde.org/show_bug.cgi?id=422050
  • !238 (merged)
• New scrolling sometimes causes crashes in QScreen::size() when PDFs are opened from other apps
  • https://bugs.kde.org/show_bug.cgi?id=425188
  • !314 (merged)
• Option in Okular to disable animated smooth scrolling transitions
  • https://bugs.kde.org/show_bug.cgi?id=420755
  • !282 (merged)
• Form fields messed up while scrolling
  • https://bugs.kde.org/show_bug.cgi?id=421354
  • !281 (merged)
• Fast scrolling with shift+scroll broke
  • https://bugs.kde.org/show_bug.cgi?id=420889
  • !298 (merged)
• Scrolling in the view goes to wrong place after scrolling using the scroll bar
  • https://bugs.kde.org/show_bug.cgi?id=421159
  • !188 (merged) (autotest only)
  • !292 (merged)
• Cursor is still a pointing hand when scrolling stops after clicking an internal link
  • https://bugs.kde.org/show_bug.cgi?id=421437
  • !176 (merged) (autotest only)
  • !297 (merged)
• Page Up/Down overlap does not work on pdf file
  • https://bugs.kde.org/show_bug.cgi?id=421950
  • !288 (merged)
• Back/forward navigation broke in 1.11.2 due to other fixes
  • https://bugs.kde.org/show_bug.cgi?id=414701
  • !295 (closed)

(optional, but highly desired) Fix minor bugs:

• No scroll animation when searching backwards
  • https://bugs.kde.org/show_bug.cgi?id=402259
  • David: This is about forgetting “PageView animated scrolling” actions completely, but fixing would be closely related to QScroller.) David: It’s indeed QScroller, probably fixed together with 422050 by !238 (merged).
• Touch/mouse grab scrolling "sticks" a bit for the first few pixels of movement
  • https://bugs.kde.org/show_bug.cgi?id=420842
  • !195 (closed)
  • !272 (merged)
• Inertia doesn't work when the mouse goes through upper/lower side of the screen to appear at the other side
  • https://bugs.kde.org/show_bug.cgi?id=420556
  • !310 (merged)
• Pinch zoom gesture often scrolls instead
  • https://bugs.kde.org/show_bug.cgi?id=421755
  • !134
  • David: This is for 390707, and not really scrolling related. I will look at this MR.
• Jittery scrolling with a free-spinning scroll wheel
  • https://bugs.kde.org/show_bug.cgi?id=427504

(Optional, can be a longer term thing) Complete the feature

• Apply smooth scrolling animated transition for arrow key scrolling and mouse wheel scrolling
  • https://bugs.kde.org/show_bug.cgi?id=422041
  • https://bugs.kde.org/show_bug.cgi?id=425850
  • c54c38f7 (completing !238 (merged))
• Smooth scroll animated scrolling transition speed does not respect the global animation speed multiplier
  • !269 (merged)
• Kinetic scrolling for trackpad scrolling
  • https://bugs.kde.org/show_bug.cgi?id=420925
• While inertially scrolling through a multi-page file, not-previously-seen pages are not rendered until scrolling ends
  • https://bugs.kde.org/show_bug.cgi?id=426504

Additionally submitted patches:

• Configuration option to disable smooth scrolling
  • !282 (merged)

Waiting for this project:

• !134
• !234 (merged)
• !292 (merged) (Need to remove QEXPECT_FAIL on master)