Open Bug 1300879 Opened 4 years ago Updated 3 years ago

Slow restyle on large page due to viewport being resized

Categories

(Core :: CSS Parsing and Computation, defect, P3)

defect

Tracking

()

Tracking Status
firefox51 --- affected

People

(Reporter: mstange, Unassigned)

Details

STR:
 1. Go to https://html.spec.whatwg.org/ and wait for it to load.
 2. Show / hide your bookmarks toolbar using View -> Toolbars -> Bookmarks Toolbar.
 3. Immediately after step 2, try to select text on the page.

The page hangs for about three seconds, doing restyling. The same happens when you open the findbar.

The restyle is triggered by nsPresContext::MediaFeatureValuesChanged.
Is it slower than just restyling everything?  Because depending on what media rules are present, that may in fact be happening....
And note that this particular page uses lots of viewport-relative units (vh and vw) last I looked, so changing the viewport height does in fact need to recalculate all sorts of stuff.  :(
(In reply to Boris Zbarsky [:bz] from comment #1)
> Is it slower than just restyling everything?

I haven't checked, because I thought restyling everything was unnecessary. But it sounds like it is necessary. Oh well.
Priority: -- → P3
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