1743795 - Canvas background is visible even though context was created with alpha:false

Status: RESOLVED DUPLICATE of bug 1449575

(Core :: Graphics: CanvasWebGL, defect, P1)

Description

[marczellm]

Attachment: Screenshot showing the actual and expected result

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.1 Safari/605.1.15

Steps to reproduce:

1. Go to https://bimx.graphisoft.com/model/0d020f3f-d95b-4941-8de1-0fd18b3bdf48
2. If on Mac or Linux, spoof the user agent, because the app limits features on Mac Firefox. This is not necessary on Windows
3. Press the big play button in the middle
4. Double click "3D model" and wait for the model to load

Actual results:

The lightmaps of the 3D scene appear white.

Our testing shows that this is a regression introduced in Firefox 93 and still reproducible in 95 beta.
It can be demonstrated that the white color is coming from the HTML page background. If I go into devtools and add a style="background-color: purple" attribute to the canvas element, the lightmaps also become purple. The canvas background should not be visible case because the webgl context was created with alpha: false.

Expected results:

The lightmaps should appear black. I've attached a screenshot showing the correct behaviour in Chrome. Firefox pre 93 works correctly as well.

Comment 1

[Alice0775 White]

I can reproduce the issue in Firefox93, 94 95.0 and Nightly96.0a1 Windows10.

Comment 2

[Alice0775 White]

Regression window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=d3801075f8d6d5883498e3d6d64eb677f1e54507&tochange=2e0d7aa9f89849b32c22453bbfbadfa06910ce5b

Comment 3

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1726265

Comment 4

[BugBot [:suhaib / :marco/ :calixte]]

The severity field is not set for this bug.
:jgilbert, could you have a look please?

For more information, please visit auto_nag documentation.

Comment 5

[Bob Hood [:bhood]]

FYI: This report is part of a P1 triage list that a "WebGL mini team" within Platform Graphics will begin addressing this week.

Comment 6

[Kelsey Gilbert [:jgilbert]]

I bet this is fixed by bug 1449575.

Comment 7

[Kelsey Gilbert [:jgilbert]]

But let's wait on it!

Comment 9

[Kelsey Gilbert [:jgilbert]]

Looks fixed to me. Can you confirm in an up-to-date Nightly?
I believe the workaround would be to use an alpha:true canvas and keep the alpha channel as opaque yourself.
Thanks for reporting this!

Comment 10

[marczellm]

I can confirm the bug appears fixed in latest Nightly.