[Libreoffice-bugs] [Bug 137794] FILEOPEN: QT5 VCL with default renderer (not cairo) is much slower at opening slides

[bugzilla-daemon at bugs.documentfoundation.org]

https://bugs.documentfoundation.org/show_bug.cgi?id=137794

Jan-Marek Glogowski <glogow at fbihome.de> changed:

           What    |Removed                     |Added
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             Blocks|                            |125943

--- Comment #1 from Jan-Marek Glogowski <glogow at fbihome.de> ---
(In reply to sergio.callegari from comment #0)
> Description:
> Trying to track the progress of the QT5 VCL, I have tried opening some
> impress documents with the QT5 VCL.
> 
> Unless I also use SAL_VCL_QT5_USE_CAIRO, the rendering of the fonts in my
> slides is extra bad (which I think is expected for the time being). However,
> I have also noticed that the slides are much much slower to open.

I wouldn't have high hopes and it's not "expected for the time being".

Unless someone decides to use not just LO's own text layouting code (which uses
harfbuzz anyway, like almost everyone), but also LO's native (AKA platform
dependent) font drawing code to replace Qt's own font drawing, the only thing
to do would be fixing Qt. My personal target is Qt only, but all patches
welcome. Or on Linux to use Cairo graphics as a workaround with a little
blitting overhead.

The Qt5 VCL plugin completely relies on Qt for font handling, so it uses QFont,
QGlyphRun and QPainter::drawGlyphRun. This way it can also work on all Qt
supported platforms without any "native" code (tested once on MacOS and Win).


Referenced Bugs:

https://bugs.documentfoundation.org/show_bug.cgi?id=125943
[Bug 125943] [META] Qt5 VCL backend bugs and enhancements
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