20449 - [Mac] scrolling of fixed positioned elements is broken

Status: VERIFIED FIXED

(Core :: XUL, defect, P3)

Description

[Pierre Saslawsky]

Sometime between M8 (July 16) and M9 (August 26), the scrolling of fixed
positioned elements has been broken. To reproduce:
- Open Sample #11
- Click the thumb on the vertical scrollbar and drag it down then up
==> The display is garbled. The problem can still be reproduced with gfx
scrollbars in recent builds.

I suspect some changes in Invalidate() or Scroll() to have caused this but I
don't remember having worked on it during that period (I was working on something
else and then on vacation). Any idea?

Comment 1

[Pierre Saslawsky]

Reassigned to Pink. The culprit is the ScrollBits() routine checked in on August
2. FYI, beard just told me that it should be possible to use ::ScrollRect()
without getting the annoying flicker by momentarily setting the window background
color to whatever we need. He mentioned a TechNote on that subject too.

Comment 2

[Mike Pinkerton (not reading bugmail)]

while i don't doubt there are problems with my scroll routine, why would using
::ScrollRect be any better? I'm not doing anything it doesn't do.

Comment 3

[Pierre Saslawsky]

It was just a suggestion, I haven't looked into either solution (keeping
ScrollBits or trying to make ScrollRect work).

Maybe the problem comes from the InvalRgn(updateRgn) that you removed from the
Scroll() function when implementing ScrollBits(). If you put it back, you may
want to use StRegionFromPool for 'updateRgn'.

Comment 4

[Mike Pinkerton (not reading bugmail)]

accepting, m15

Comment 5

[Pierre Saslawsky]

I would like to fix this before M15. Can I put back the Invalidate() and mark you
as reviewer?

Comment 6

[Mike Pinkerton (not reading bugmail)]

heck if that is all that it takes to fix it, then go right ahead!!! r=pinkerton!

Comment 7

[Pierre Saslawsky]

It required a little bit more than that: we had to take into account the visible
region when computing the source/dest rects and the updateRgn.

I verified that it worked with horizontal and vertical scrolling, with a fixed
element in the middle of the page floating above the rest, and with the OS 8.5
floating palette from the Apps menu.

Comment 8

[Claudius Gayle]

I'm marking this VERIFIED because it passes test #11 on Debug|Viewer Demos
but I also passing off the QA to petersen cuz it rally is the smae bug as bug 20185
and I'm sure you're all over that :-)
verified with the 2000011310 build on Mac OS 8.5.1

Comment 9

[Pulsebot]

Pushed by ffxbld-merge:
https://hg.mozilla.org/releases/mozilla-beta/rev/2b12e78a2efd
[fenix] For https://github.com/mozilla-mobile/fenix/issues/20449 - Fixes `Show most visited sites` crash on disable