1266036 - Firefox is displayed on entire screen bypassing windows snap assist functionality when using two screens

Status: RESOLVED WORKSFORME

(Core :: Widget: Win32, defect)

Description

[Bogdan Maris, Desktop QA]

[Affected versions]:
- Windows 10 64-bit

[Affected platforms]:
- latest Nightly 48.0a1
- latest Developer Edition 47.0a2

[Steps to reproduce]:
- Prerequisits: one low and one hidpi monitors.

1. Start Firefox and move it to low dpi screen
2. Start another program
3. Grab the program and snap it on one side
4. Select Firefox to fill the other half of the screen (A list of all opened programs appear when moving other programs to side of screen)

[Expected result]:
- Firefox successfully fills the other half of the screen

[Actual result]:
- Firefox is displayed on the entire screen. On older builds its even worse

[Regression range]:
- This is a recent regression caused by:
29e1faddbf53	Jonathan Kew — Bug 1246389 - Resize window appropriately on WM_DPICHANGED messages for dynamic resolution changes. r=emk

m-c

Last good revision: 8ef94be995a453f5c464278c53478ba8c8554f81
First bad revision: 5cafa6f3019b57c43312a75e7d7d58aeb032f1bc
Pushlog:
https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=8ef94be995a453f5c464278c53478ba8c8554f81&tochange=5cafa6f3019b57c43312a75e7d7d58aeb032f1bc

m-i

Last good revision: c7ffc4e71ecb8732c4c25721b1a318ac7cf247d9
First bad revision: 29e1faddbf53b86bf94f7554fe30c3f03f715cfe
Pushlog:
https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=c7ffc4e71ecb8732c4c25721b1a318ac7cf247d9&tochange=29e1faddbf53b86bf94f7554fe30c3f03f715cfe

[Additional notes]:
- Firefox 46.0 and 45 are not affected.

Comment 1

[Bogdan Maris, Desktop QA]

A few more information here:
- Firefox must be on lowdpi screen and Chrome (or other program) on hidpi for Firefox to fill the entire screen. If Firefox is opened on hidpi and other program on lowdpi is snapped to a side from lowdpi, Firefox will be resized at (width/height 418x408 - x:-640,y:793). 

Configuration:
devicePixelRatio scale: lowdpi 1680x1049 (size of text from control panel 100%), hidpi 1920x1079 (size of text from control panel 200%).

Comment 2

[Jonathan Kew [:jfkthame]]

I've been trying to reproduce this with current Nightly on a Win10 system (hi-dpi screen 2880x1620, 200%; lo-dpi 1920x1200, 100%), but the problem isn't happening here; the window always snaps to the second half of the screen, as expected.

Comment 3

[Bogdan Maris, Desktop QA]

I'm unable to reproduce this as well with latest Nightly and Developer Edition, I'll go ahead and mark the bug as works for me.