[okular] [Bug 426504] New: Pages are not rendered while inertially-scrolling through a multi-page file

[Brendon Higgins]

https://bugs.kde.org/show_bug.cgi?id=426504

            Bug ID: 426504
           Summary: Pages are not rendered while inertially-scrolling
                    through a multi-page file
           Product: okular
           Version: 1.11.0
          Platform: Debian testing
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: okular-devel at kde.org
          Reporter: brendon at quantumfurball.net
  Target Milestone: ---

SUMMARY

New pages that come into view, which have not previously been rendedered, are
not rendered while inertially-scrolling through a multi-page file. They are
only rendered once the scrolling animation stops.

STEPS TO REPRODUCE
1. Open a multi-page file (I've tested PDF and CHM files).
2. Grab the page and fling it once so that Okular starts inertially scrolling
through the pages at decent speed.
3. Watch the pages come into view.

OBSERVED RESULT

After the first couple of pages (maybe related to a performance setting?)
subsequent pages are all unrendered (blank, except for the Okular icon in the
top left corner of the page). It doesn't seem to be related to the complexity
of the pages, and continues even as the scrolling animation slows down. As soon
as the inertial scrolling stops or the user grabs the page, the page(s) in view
are rendered. The renderer seems to be waiting for the scrolling to stop.

EXPECTED RESULT

Pages are rendered as/before they come into view.

SOFTWARE/OS VERSIONS
KDE Plasma Version: 5.17.5
KDE Frameworks Version: 5.70.0
Qt Version: 5.14.2

ADDITIONAL INFORMATION

With this bug, inertial scrolling is not useful for scanning through a document
(otherwise it might be a good use-case; e.g. looking for a half-remembered
figure). I haven't seen this behaviour with any of the regular scrolling
methods. PgUp/PgDown may just move too slowly to show the effect (especially
with #422050, but perhaps now that's fixed...), even though it uses animation.

No-one else noticed this? Or maybe something is messed up in my config?
Honestly not sure - sorry for the noise, if it's just me.

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