[Libreoffice-bugs] [Bug 138068] When there are a lot of pictures, typing the text is very slow (macOS/GTK3/GDI)

[bugzilla-daemon at bugs.documentfoundation.org]

https://bugs.documentfoundation.org/show_bug.cgi?id=138068

--- Comment #28 from Luboš Luňák <l.lunak at collabora.com> ---
I tend to agree that this belongs rather in the lower levels. I'm admittedly
not very knowledgeable about the higher levels, but I wonder how they would
know how to actually do the caching. I mean, how can it know what the actual
result will be, unless every place calling the lowlevel functions basically
duplicates some of the logic?

As for the cache in Writer, if these is one, then it apparently does not work.
The only reason why the Skia backend is not hit by this is because it has its
own implementation of a cache.

And the Skia library provides SkImage::uniqueID() that changes on every content
change, so it's pretty easy to do caching there. Possibly the only case when it
wouldn't work and a cache might make sense on a higher level would be if there
are places of code that modify the to-be-drawn bitmap on every invocation e.g.
in order to apply transparency or some effect (i.e. the pixel data would be the
same, but conceptually it would be a different bitmap). But even in that (IMO
broken from a performance point of view) case I doubt higher levels would have
an easier time caching that.

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