Generate page previews even more lazily

[jdm]

I have a 74 page paper from the ACM open in the FF addon (FF nightly), and if I happen to mouse over the sidebar such that it opens, generating the previews for all 74 pages slows FF to a standstill for at least a minute. It's hard to tell who is at fault here, but I think that the best solution is to generate previews as needed - if I don't scroll the list (and in fact close the sidebar), there shouldn't be any need to generate any previews that aren't in view.

[joneschrisg]

By "slows to a standstill", do you literally mean unresponsive, or very slow?

[jdm]

It beachballs for seconds at a time, and the UI is only active in short bursts in between.

[joneschrisg]

Sounds like we're not interrupting main-thread canvas drawing frequently enough. @jviereck @brendandahl

[jviereck]

I've opened #817 to tackle the "don't freeze the UI during canvas rendering" thing. The "render preview not from 1 to X" is not part of that issue.

[brendandahl]

I think there's two problems:

1. The sidebar currently isn't very "smart" and it starts from the first page and starts rendering every single preview.
2. We need to fiddle with the drawing interrupt timing and probably look into doing a waited counter like poppler does.

There's more on 1 in issue #780

[brendandahl]

I believe this has been resolved with #854. If I missed something feel free to leave a comment and I'll re-open the issue.