User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:72.0) Gecko/20100101 Firefox/72.0

Steps to reproduce:

I use a non default theme (Seagull v2)

Actual results:

The window buttons (minimize, close) are visually missing, but they are present, I can click on them.

Expected results:

Visible window buttons

This prefs are needed :
gfx.webrender.all true
gfx.webrender.enabled true

Mozregression log :

2019-11-26T10:27:48: INFO : Narrowed inbound regression window from [0acd7eb3, 4d9f2492] (3 builds) to [12df7898, 4d9f2492] (2 builds) (~1 steps left)
2019-11-26T10:27:48: DEBUG : Starting merge handling...
2019-11-26T10:27:48: DEBUG : Using url: https://hg.mozilla.org/integration/autoland/json-pushes?changeset=4d9f24928383f3da9fe40a2900a403ceb76c5983&full=1
2019-11-26T10:27:49: DEBUG : Found commit message:
Bug 1592739 - Stop using the vibrant region as the transparent region. r=mattwoodrow

Confirmed on today's build on windows 7

Possibly the same root cause as Bug 1598614. Seems important for us to investigate promptly since this is a pretty bad rendering bug in a not-wildly-ridiculous config.

(In reply to Sébastien Desvignes from comment #3)

Mozregression log :

2019-11-26T10:27:48: INFO : Narrowed inbound regression window from [0acd7eb3, 4d9f2492] (3 builds) to [12df7898, 4d9f2492] (2 builds) (~1 steps left)
2019-11-26T10:27:48: DEBUG : Starting merge handling...
2019-11-26T10:27:48: DEBUG : Using url: https://hg.mozilla.org/integration/autoland/json-pushes?changeset=4d9f24928383f3da9fe40a2900a403ceb76c5983&full=1
2019-11-26T10:27:49: DEBUG : Found commit message:
Bug 1592739 - Stop using the vibrant region as the transparent region. r=mattwoodrow

I find this really surprising. I've gone through all the changesets in that push and the only two changesets that even touch code that's not Mac-only are these two:

• https://hg.mozilla.org/integration/autoland/rev/f4b92056ed05cb75bdba417d052743ba873990a9
• https://hg.mozilla.org/integration/autoland/rev/fdbf0586295d3aa444d4cb54a183ee9ba3273011

And I'm still under the impression that the cross-platform code removed in the former was unused on Windows. And I don't have an explanation for how the latter could have caused this. So I'm a bit stumped.

(In reply to Markus Stange [:mstange] from comment #6)

I find this really surprising. I've gone through all the changesets in that push and the only two changesets that even touch code that's not Mac-only are these two:

• https://hg.mozilla.org/integration/autoland/rev/f4b92056ed05cb75bdba417d052743ba873990a9
• https://hg.mozilla.org/integration/autoland/rev/fdbf0586295d3aa444d4cb54a183ee9ba3273011

And I'm still under the impression that the cross-platform code removed in the former was unused on Windows. And I don't have an explanation for how the latter could have caused this. So I'm a bit stumped.

When I've run mozregression for the first time and discovered the potential bug, I was surprised too. So I've run mozregression again, but with the same result...

There is also this change that isn't Mac specific (the line outside the #ifdef) :

-#ifdef XP_MACOSX
-      opaqueRegion =
-          mCompositor->GetWidget()->GetOpaqueWidgetRegion().ToUnknownRegion();
-#endif
-      opaqueRegion.AndWith(mRenderBounds);
+      opaqueRegion.And(aOpaqueRegion, mRenderBounds);

https://hg.mozilla.org/integration/autoland/rev/4d9f24928383f3da9fe40a2900a403ceb76c5983

However, I have no idea if this can be related.

Markus have you been able to track this down?

I've built Firefox from sources and I've found that this change is responsible for the regression :
https://hg.mozilla.org/integration/autoland/rev/fdbf0586295d3aa444d4cb54a183ee9ba3273011
When I revert those lines, the bug is fixed.

That's incredibly helpful! Thank you so much! Still need to think about how exactly it would affect things...

I'm planning to have bug 1592739 backed out from 72 so that I have more time to track this down.

https://hg.mozilla.org/releases/mozilla-beta/rev/e3a91b611720

https://hg.mozilla.org/releases/mozilla-beta/rev/ff911052beb1

Calling 72 & 73 fixed by backout.

Regressor backed out for 74 and 75 now too:
https://hg.mozilla.org/releases/mozilla-beta/rev/fee92a1f6d6ec6ea10f6c431439dfaea26e54baa
https://hg.mozilla.org/integration/autoland/rev/ecc5c853bb770cc3f9acc90d9ed9febe086671a0

Hi Sébastien, the patch that originally caused this bug has now relanded, but in a different form that should hopefully avoid triggering this bug again. Could you confirm whether this bug is still fixed?

Tested Nightly 2020-06-21 with WebRender on Win7 with Aero, Basic and Classic themes: This bug didn't come back.

Thanks!