1766584 - Drop-shadow renders wrong for blur-radius 1px on 150% scaling displays

Status: RESOLVED DUPLICATE of bug 1765013

(Core :: Graphics: WebRender, defect, P3)

Description

[raimund.schluessler+github]

Attachment: 00_1px_150%_broken.png

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:99.0) Gecko/20100101 Firefox/99.0

Steps to reproduce:

Have a div element and apply the CSS filter drop-shadow with a blur-radius of 1px and no x or y offset like so

filter: drop-shadow(0px 0px 1px #4444dd);

Look at the resulting drop-shadow on a display with scaling set to 150 %.

Actual results:

The drop shadow is offset to the top left and does not show on all sides of the element if is is viewed on a display with the scaling set to 150 %. Taking a screenshot with the Firefox screenshot tool shows the correct result, though (hence, the screenshot shows a different image than displayed to the user in Firefox).
A drop-shadow with a blut-radius larger than 1 px works fine as well.

Expected results:

The drop-shadow should render symmetrically on all sides of the element if no offset is given even with a blur-radius of 1px.

Comment 1

[raimund.schluessler+github]

Attachment: 01_2px_150%_good.png

Comment 2

[raimund.schluessler+github]

Attachment: 02_1px_150%_screenshot_good.png

Comment 3

[raimund.schluessler+github]

Attachment: 03_2px_150%_screenshot_good.png

Comment 4

[Jamie Nicol [:jnicol]]

Thanks for the bug report. Could you please go to about:support, click on "copy text to clipboard", and add it as an attachment to this bug? Thanks

Comment 5

[raimund.schluessler+github]

Attachment: about_support_win.txt

Comment 6

[raimund.schluessler+github]

While playing a bit more with the drop-shadow, I realized the issue is not limited to 1px blur-radius and a certain screen scaling, but occurs at various combinations of website zoom and blur-radius with varying intensity. While zooming in and out, the position of the drop-shadow behind the element changes. I attached a GIF to show the issue better.

This happens on both my Windows machine (for which I added the about:support config) and my Ubuntu machine (22.04, bundled Firefox). Let me know if you want the about:support config of the Linux machine as well.

Comment 7

[raimund.schluessler+github]

Attachment: DropShadow.gif

Comment 8

[Jamie Nicol [:jnicol]]

Seems like this could be a snapping issue? Any ideas Andrew?

Comment 9

[Jamie Nicol [:jnicol]]

Thanks for the link, Mayank.

Raimund, could you please test version 100 and see if this issue has now been fixed?

Comment 10

[raimund.schluessler+github]

Yes, indeed it is fixed in FF 100. Thank you very much!