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[Adam Reichold <question234962@xxxxxxxxxxxxxxxxxxxxx>]

Question #234962 on qpdfview changed:
https://answers.launchpad.net/qpdfview/+question/234962

    Status: Open => Answered

Adam Reichold proposed the following answer:
Hello Arnaud,

I think that there are two points to make here:

* Concerning the comparison with xpdf (On which AFAIK Poppler is
originally based, not the other way around?), I think it does rendering
synchronously, i.e. blocking the interface while doing it, so while it
will compute a single state change faster, the responsiveness of the
interface is generally worse.

* The reason for the progress icon being displayed is that the graphics state (e.g. bounding rectangle and so on) is updated, but rendering is only initiated in a background thread, with the result being displayed as soon as it is available. We used to have an build-time option to disable background rendering, but it really makes the interface harder to use.
One useful way of going about this is to scale up the already rendered image up to the new size until the higher-resolution rendering is finished (this is for example done in Okular). But while this is a nice feature, I have never felt the urge to implement it since the activity is indicated by the progress icon without introducing another state to the rendering process and further delaying the freeing of the buffer containing the obsolete image.

In short, at the moment, I don't really see the necessity to implement
this and thereby complicating the rendering process.

Best regards, Adam.

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