1614167 - [wayland][WebRender] Firefox UI is scaled incorrectly on non-integer scale factors, if started on integer scale factor

Status: RESOLVED DUPLICATE of bug 1612377

(Core :: Widget: Gtk, defect, P2)

Description

[Cole Mickens]

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:74.0) Gecko/20100101 Firefox/74.0

Steps to reproduce:

Video repro: https://www.youtube.com/watch?v=gIKwD5U3LCo

1. Set Sway output scale = 1
2. Start firefox
3. Set Sway output scale = 1.1, then 1.2

Actual results:

4. Notice that Firefox is (poorly) scaled to something more like 2x.
5. Notice that Chromium (Ozone/Wayland) has done the correct thing.

Then repeat the scenario, but first set the output scale to 1.2, THEN start firefox. This time, it is somehow able to handle the fractional scaling down and back up.

This bug repros in another way, but I don't have a screenshot of it yet, it seems to require using an external monitor (or possibly requires starting with the output at 2.0 and then moving down, I suspect it might trigger the bug the same way.)

Expected results:

I expected it to behave like earlier Nightly builds on Wayland and correctly handle the fractional scaling, (as it seems it can still do if you trick it).

Comment 1

[Cole Mickens]

Exact version: 74.0a1 (2020-02-08) (64-bit)

Comment 2

[Cole Mickens]

It seems to be related to the integer boundaries.

If I set the output scale to 2.0, then lower it, I can go 1.9, 1.8, ... 1.1, and it's fine.
As soon as it gets to 2.0, it snaps to being far too small.

Comment 3

[Cole Mickens]

Attachment: output.png

Comment 4

[Cole Mickens]

Comment 2 with a correction (I had the ending scale written incorrectly):

"If I set the output scale to 2.0, then lower it, I can go 1.9, 1.8, ... 1.1, and it's fine.
As soon as it gets to 1.0, it snaps to being far too small." (the screenshot posted shows this scenario)

It also seems if you start with scale=1, then go up to 2, you can't go back to 1, you end up with the same result (again, see same screenshot).

Comment 5

[Martin Stránský [:stransky] (ni? me) (PTO, back on Feb 17)]

Can you check if that's webrender only? Please disable webrender at about:config.

Comment 6

[Cole Mickens]

@stransky, it looks like it is related to webrender. I set it forced-disabled=true and it seems like it's back to behaving correctly.

Comment 7

[Martin Stránský [:stransky] (ni? me) (PTO, back on Feb 17)]

I see, thanks. WebRender has some bugs with DPI changes, I'll look at it. Bug 1612377 may be a dupe.

Comment 8

[Cole Mickens]

The thanks goes to you Martin, I see your name a lot on these Wayland bugs. Thank you for the work!

It's almost certainly a dupe of that bug. I'll resolve this as dupe.