1918802 - Simplify scrollbar track drawing.

Status: RESOLVED FIXED

(Core :: Widget, defect)

Comment 1

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1918802 - Simplify scrollbar track drawing. r=spohl,mstange,#mac-reviewers

This was caught by Markus. When you hover over an overlay scrollbar on
macOS, you'd hit this the PaintScrollbar() code-path (or rather, you
won't bail out from the if (overlay && !hovered)), but macOS draws the
track in PaintScrollbarTrack().

Android doesn't hit this because android scrollbars can't ever be
hovered (they have pointer-events: none). This is a better fix than
D222172, which didn't paint the background for the non-overlay
scrollbars...

This doesn't change behavior since scrollbar and the thumb have the same
size (as cocoa scrollbars can never have buttons). Removing
nsSliderFrame is a refactor for another day if ever.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5db7dce4900f
Simplify scrollbar track drawing. r=mstange,mac-reviewers

Comment 3

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/5db7dce4900f

Comment 4

[Florin Bilt]

(In reply to Norisz Fay [:noriszfay] from comment #3)

https://hg.mozilla.org/mozilla-central/rev/5db7dce4900f

Perfherder has detected a browsertime performance change from push 5db7dce4900f2bbcca3266086489cf9aaee3ec52.

Improvements:

Ratio	Test	Platform	Options	Absolute values (old vs new)	Performance Profiles
2%	cnn ContentfulSpeedIndex	linux1804-64-shippable-qr	fission warm webrender	606.32 -> 591.66	Before/After
2%	cnn FirstVisualChange	linux1804-64-shippable-qr	fission warm webrender	589.31 -> 576.78	Before/After

Details of the alert can be found in the alert summary, including links to graphs and comparisons for each of the affected tests.

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