1494514 - Link-open triggered from a low-DPI window but opened on high-DPI window renders as 1/4 size

Status: NEW

(Core :: Layout, defect, P3)

Description

[Logan Smyth [:loganfsmyth]]

Attachment: bug-low-dpi.tgz

This sounds related to https://bugzilla.mozilla.org/show_bug.cgi?id=1480182 but I figured I'd file it separately since I couldn't quite tell.

On Gmail's chat, someone sent me an image. I had the chat window open on a low-DPI screen. When I clicked the link, the image opened in my primary browser window, but rendered at 1/4 size. Dragging the window between screens triggers a resize and fixes rendering.

I created a simple reproduction to make everyone's life easier.

Reproduction:
1. Extract the attached tgz
2. Run `python -m SimpleHTTPServer 8001` to serve the files
3. Open localhost:8001
4. Click the link to open a popup
5. Drag the popup onto a low-DPI screen
6. Click the link in the popop

Expected:
The cat gif should open in the original primary browser window at normal size.

Actual:
The cat gif opens on the high-DPI screen, but the window content is rendered a 1/4 scale.

Comment 1

[Logan Smyth [:loganfsmyth]]

Attachment: cat window rendered as 1/4 of the window

Comment 2

[Neil Deakin]

A quick look suggests that nsPresContext::mCurAppUnitsPerDevPixel is initialized to the wrong value when the window opens.

Seems to be specific to when a window is opened, as in this test, via 'window.parent.open(...)' For example, at step 5, zoom the popup window a bit, and the new window in step 6 will be zoomed by that amount as well. I assume the scale is being incorrectly inherited from the parent window.

Comment 3

[Emilio Cobos Álvarez [:emilio]]

I took a look and the nice thing is that this repros on wayland too, so it should be trivial to debug with RR.

Bad thing is that I'm hitting https://github.com/mozilla/rr/issues/2331 all the time when trying to do so.