[Bug 307544] PDF Thumbnails are created very slowly in Okular Active

[Thomas Pfeiffer]

https://bugs.kde.org/show_bug.cgi?id=307544

--- Comment #2 from Thomas Pfeiffer <colomar at autistici.org> ---
You are absolutely correct. I wrote this bug report purely from a user's
perspective and did not try to abstract from that and switch to a UX
professional's perspective, sorry about that.

The problem we're facing here is not that something needs time, it is how the
user _perceives_ it. When I open the drawer, I see a grid with mostly
placeholders and a few thumbnails scattered here and there. I don't _see_ that
the system is still working to create more thumbnails, it just looks broken
(look at it again yourself, you'll notice it).
So if it is not possible to create the thumbnails faster, we need to convey to
the user "Okay, these are the pages of your document. Normally I would present
thumbnails of them to you, but I'm still busy creating them". This is not
conveyed by the current UI. Currently a user thinks "Hey, why do some pages
look like the real ones, but most others like placeholders?"

The actual rendering in the main view does a better job here: It starts with a
blurry image of the page which is gradually sharpened as the details are
rendered. Since I know that my document isn't really all blurry, I understand
that the rendering is still at work.
So how long would it take to create a very blurry thumbnail (just sharp enough
that not all pages look _exactly_ the same to users)? If that is quicker, than
I'd suggest rendering very blurry thumbnails at first and then gradfually
replacing them with sharper ones. I bet users will hardly notice what's
happening.
If that would take almost as long as it takes to create the current ones, we
need a different solution.

Actually, I'd say the thumbnail for the currently viewed page should be
rendered first. This is not the case right now and it looks extremely weird
when I see the crystal clear page before me in the main view but when I open
the drawer, that same page is still a placeholder. Users don't understand that
rendering the main view and rendering the thumbnail are independent processes,
and it just looks totally broken.
Genereally I'd expect the thumbnails to be rendered as fast as the main view,
so when I look at each page long enough to be fully rendered, its thumbnail
should be there as well. Again, this is currently not the case. It takes longer
to render thumbnails for X pages than it takes to render the actual pages.

So here is a measurable time for the rendering of a thumbnail: At maximum as
long as it takes to render the page in the main view.

(Sorry for the very long comment. I just realized that this is actually a
pretty delicate UX task.)

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