1875011 - Use non-rounded scroll position in nsHTMLScrollFrame::ScrollByCSSPixelsInternal behind layout.scroll.disable-pixel-alignment pref

Status: RESOLVED FIXED

(Core :: Layout: Scrolling and Overflow, task)

Description

[Hiroyuki Ikezoe (:hiro)]

We use rounded scroll positions in nsHTMLScrollFrame::ScrollByCSSPixelsInternal, it is the cause of 1px difference failure in the wpt added in bug 1874551.

Comment 1

[Hiroyuki Ikezoe (:hiro)]

Attachment: Bug 1875011 - Rename GetScrollPositionCSSPixels to GetRoundedScrollPositionCSSPixels. r?botond

Comment 2

[Hiroyuki Ikezoe (:hiro)]

Attachment: Bug 1875011 - Use non-rounded scroll position behind layout.scroll.disable-pixel-alignment in nsHTMLScrollFrame::ScrollByCSSPixelsInternal. r?botond

Depends on D198766

Comment 3

[Hiroyuki Ikezoe (:hiro)]

Note that nsHTMLScrollFrame::ScrollToCSSPixels also uses the rounded scroll position but I leave it as it is for now since it's entirely unclear to me about the following comparisons in the function;

  // XXX I don't think the following blocks are needed anymore, now that
  // ScrollToImpl simply tries to scroll an integer number of layer
  // pixels from the current position
  nsPoint current = GetScrollPosition();
  if (currentCSSPixels.x == aScrollPosition.x) {
    pt.x = current.x;
    range.x = pt.x;
    range.width = 0;
  }
  if (currentCSSPixels.y == aScrollPosition.y) {
    pt.y = current.y;
    range.y = pt.y;
    range.height = 0;
  }

As the comment said, I guess it's not necessary, but if it's still necessary, or if we leave the comparison here in this bug, comparing CSSPoint with CSSIntPoint would be problematic. If we round the CSSPoint value for the comparison, it would be identical to the current version in most cases.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/8a492fe4ed55
Rename GetScrollPositionCSSPixels to GetRoundedScrollPositionCSSPixels. r=botond
https://hg.mozilla.org/integration/autoland/rev/e6395c398b89
Use non-rounded scroll position behind layout.scroll.disable-pixel-alignment in nsHTMLScrollFrame::ScrollByCSSPixelsInternal. r=botond

Comment 5

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/8a492fe4ed55
https://hg.mozilla.org/mozilla-central/rev/e6395c398b89

Comment 6

[Pulsebot]

https://hg.mozilla.org/releases/mozilla-release/rev/e0878b830cd7
https://hg.mozilla.org/releases/mozilla-release/rev/9ad9c0b225e2