D9328: Add support for cancellable image rendering and text extraction

[Michael Weghorn]

michaelweghorn added a comment.


  I tested this a bit and find it really nice that rendering of the actual page (rather than the thumbnail) usually starts at once when re-rendering is needed (e.g. when zoom level is changed).
  Also, closing Okular now works fast, even if rendering is still in progress. (The shell prompt is shown almost immediately after closing Okular when it was started from the command line.)
  
  While the above is true most of the time, it happens from time to time that rendering does not start at once.
  I can reproduce this e.g. the following way:
  
  - open a file that takes long to render
  - zoom "one step" in and out every few seconds (using the mouse wheel)
  
  While re-rendering is triggered most of the times at once, the page sometimes remains "blank" for more than 30 seconds.
  In those cases where the page is "blank", it also takes long for the Okular process to finish when closing the program at that point in time.
  
  I (temporarily) uploaded a screencast here: https://ombx.io/4SDa42mm
  
  Another thing I realized is that re-rendering is now triggered every time the zoom level is changed.
  Without this change, rendering the page is sometimes just continued at the place where it was before changing the zoom level (which results in the final page appearing earlier when no re-rendering is needed).

REPOSITORY
  R223 Okular

REVISION DETAIL
  https://phabricator.kde.org/D9328

To: aacid
Cc: michaelweghorn, ngraham, #okular, gassaf, aacid
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