[Webkit-unassigned] [Bug 41036] REGRESSION (r61341): Image interpolation quality changes during scrolling and when activating / deactivating application

Wed Jun 23 11:48:11 PDT 2010

https://bugs.webkit.org/show_bug.cgi?id=41036

--- Comment #4 from Stephen White <senorblanco at chromium.org>  2010-06-23 11:48:10 PST ---
(In reply to comment #3)
> The attached page still shows poor performance with your change: all of the images change interpolation quality at once, leading to hangs of between half and one and a half seconds as every image is resampled at once.  Maybe this is better than it was, but it hardly seems like ideal performance.

The main difference is that the delay/hang happens only when you stop scrolling, rather than on every mouse move.  Without the patch, scrolling is unusable.  You're right that it's not ideal, but it's better than it was.

> I have to confess that I don’t really understand what is going on here.  It appears that any time we’re asked to repaint the image we first repaint it using the lower interpolation quality before repainting it at the higher interpolation quality.  This leads to a very visible shift in the image after changing tabs, scrolling, deactivating the window, activating the window, forcing the window to repaint via the Debug menu, etc.  I don’t think that this shifting is acceptable on pages that are clearly not doing anything heavyweight (whether it be resizing images rapidly or having many tens of resized images).  Whatever heuristic is being used to determine when to use the lower-quality interpolation needs to be smarter than just blindly doing it whenever a resized image repaints.

Actually, it sounds like you understand exactly what's going on.  You just don't like it, which is fair.

I've put together another patch that's more like the original behaviour, and I'll attach it to this bug so we can talk about it.  I'm still more happy with the original patch, since it's less janky, but I think this might be an acceptable compromise.

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