[DNSB]

Originally Posted by shopma2

Hi
When I load an epub from calibre 8 to my Kobo it is displayed with a much smaller font on the Kobo than books from the previous calibre version. In the calibre epub editor on my PC the font size is NOT different.
When I copy the epub from the Kobo back to the PC and view it the font size is normal.
When I uninstall calibre 8 and use calibre 7.26 to load the ebup on the Kobo the problem does not occur.

You can either uncheck Use Kobo viewer for EPUB books to disable the conversion to kepub.epub or use the KoboPatcher Unify Font Sizes patch to make the base font size in ePub and Kepub books match. The patch is the solution I use since it allows me to switch renderers without a noticeable font size change.

Kobo uses 2 renderers, one is the Adobe RMSDK renderer which is needed to compatibility with ePubs that use Adobe's ADEPT DRM while the other is WebKit based with much better ePub3 support which supports Kobo's proprietary DRM.

Unify font sizes:
  - Enabled: no
  - Description: |
      Attempt to unify the font sizes between epub and kepub. Without this patch
      epub font sizes can be much larger than kepub at the same size setting.
    # From my current understanding, the final font size for epubs is calculated
    # as follows: ( font_size / scale_factor ) * DPI, where 'scale_factor' =
    # 25.0. It seems RMSDK must be handling DPI elsewhere however, because the
    # DPI multiplication here seems to have a detrimental effect, and behaves
    # differently on different devices. This patch changes the 'scale_factor' to
    # 2.5, and replaces the call to get DPI with a constant multiplier (16).
    # The results of using these values are equivalent to  
    # ( font_size / 15.0 ) * 96 which is what I suspect the kepub formula is.
    # Note, that the replacement values are limited to 0.25 - 31.0 in 0.25
    # increments.
    #
    # Refer to https://github.com/pgaskin/kobopatch-patches/issues/96 for more
    # information.
  # EPUB settings:
  - BaseAddress:
      Sym: "AdobeStyling::update(QString const&)"
      Rel: 5796 # at ReadingSettings::getReadingFontSizeScaleFactor(float, float)
  # Set the scale factor to 2.5
  - ReplaceBytes:
      Offset:   -20
      FindH:    F3 EE 09 0A # vmov.f32 s1, #25.0
      ReplaceH: F0 EE 04 0A # vmov.f32 s1, #2.5
  # Replace QScreen::logicalDotsPerInchX() with our own multiplier of 16.0
  - ReplaceBytes:
      Offset:      26
      FindInstBLX: {SymPLT: "QScreen::logicalDotsPerInchX() const"}
      ReplaceH:    B3 EE 00 0B # vmov.f64 d0, #16.0