[okular] [Bug 385200] New: Low resolution rendering when using display scaling on HiDPI monitor

[Markus Krötzsch]

https://bugs.kde.org/show_bug.cgi?id=385200

            Bug ID: 385200
           Summary: Low resolution rendering when using display scaling on
                    HiDPI monitor
           Product: okular
           Version: 1.2.1
          Platform: Neon Packages
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: okular-devel at kde.org
          Reporter: markus at semantic-mediawiki.org
  Target Milestone: ---

Created attachment 108087
  --> https://bugs.kde.org/attachment.cgi?id=108087&action=edit
Okular's low resolution view in comparison to Evince

On a high-resolution display (QHD+), Okular's font rendering is noticeably
inferior to the rest of the desktop, and also to the rendering in Evince.
Looking closely, it appears that the displayed image is a scaled-up version of
a lower resolution rendering. This occurs across all formats that I have tested
(PDF, PS, ODT).

The attached screenshot illustrates the problem, showing the same PDF in Okular
(left) and Evince (right).

This is a HiDPI monitor, and I am using KDE's built-in "scale" option set to
"2" (System Settings -- Displays and Monitor -- Displays: Scale Display). It
seems plausible that Okular wrongly applies this scaling by first rendering the
file in a low resolution and then scaling the resulting bitmap, instead of
producing a bitmap using the scaled resolution right away (i.e., it applies
bitmap scaling to a vector graphics). Otherwise I am on KDE Neon at default
settings for Okular and Evince. I changed Okular's memory setting to
"aggressive" without any effect on this issue.

I do not think that this bug is related to any other font rendering issues
associated with display scaling. The rest of my desktop is looking excellent
(making Okular stick out even more).

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