[Okular-devel] [Bug 310651] New: Replace zoom level 33% with 1/3

[Jaan Vajakas]

https://bugs.kde.org/show_bug.cgi?id=310651

            Bug ID: 310651
          Severity: normal
           Version: 0.15.80
          Priority: NOR
          Assignee: okular-devel at kde.org
           Summary: Replace zoom level 33% with 1/3
    Classification: Unclassified
                OS: Linux
          Reporter: jaanvajakas at hot.ee
          Hardware: openSUSE RPMs
            Status: UNCONFIRMED
         Component: general
           Product: okular

DjVu files (and most probably other raster formats too, in case of images with
sharp edges) are much sharper at zoom levels that are unit fractions or
multiples on 100%, i. e. 100%/n or n*100% where n is a natural number. So I
think the zoom level 33% should be replaced with something like 33.333333333%
(maybe displayed to the user as 33.33% or 1/3). Similarly, 12% should be
replaced with 1/8=12.5%. For consistency, 66% should probably be replaced with
2/3=66.666666667% as well, although the sharpening effect is smaller in that
case.


Reproducible: Always

Steps to Reproduce:
1. Open a DjVu file containing some text.
2. Set zoom to 33% using the zoom drop-down box.
3. Type manually 33.3333333 in the zoom field and press <Enter>.
4. Close Okular.
5. Reopen the DjVu file in Okular.
Actual Results:  
After step 2, the text is quite blurry. After step 3, the text becomes much
clearer (although Okular displays 33.33% as the zoom level, it seems that it
actually uses 33.3333333). After step 5, Okular again displays 33.33% as the
zoom level, but the text is blurry again, so it seems that Okular has rounded
off the zoom level when saving the view settings.

Expected Results:  
* The zoom drop-down box should contain the value 1/3=33.33333333333% in the
first place instead of 33% (and similarly 12.5% instead of 12% and
2/3=66.66666666667% instead of 66%).
* When saving the view settings, higher precision should be used for the zoom
level so that the same zoom level would be restored after closing and reopening
a document.

The blurriness could also be significantly mitigated by subpixel rendering (Bug
#276199) which would have its own merits as well. But even with subpixel
rendering, unit fractional zoom levels would give better results.

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