Green on:
Chrome version	Chrome/69.0.3497.100
Operating system	Mac OS X 10.13.6
Machine model name	MacBookAir
Machine model version	7.2
GL_VENDOR	Intel Inc.
GL_RENDERER	Intel(R) HD Graphics 6000
GL_VERSION	4.1 INTEL-10.36.19

So I guess it's very hardware specific.

Yang, Yunchao: could you please triage this bug on whatever Mac hardware you have available and see how many GPU types it affects?

Sure, we will triage. 

Able to reproduce the issue on MacBook Pro (Retina, 15-inch, Mid 2015) 10.13.3 using chrome reported version #69.0.3497.100 and latest canary #71.0.3556.0. Issue is specific to OS-mac.
This is a non-regression issue as it is observed from M60 old builds. 

Hence, marking it as untriaged to get more inputs from dev team.

Thanks...!!

I can only reproduce the issue on MacBook Pro (Retina, 15-inch, Mid 2015, Intel Iris Pro). 

Here are the devices I have tested (macOS version is 10.13.6)


Macbook Pro Mid 2015 (15-inch) 10.13.6, Intel Iris Pro)	69.0.3497.100 	Red
Macbook Pro 2017 (13-inch, Iris Graphics 650)			69.0.3497.100	Green
Macbook Pro 2018 (13-inch, Iris Plus Graphics 655)		70.0.3514.2 	Green
Macbook Early 2016 (12-inch, HD Graphics 515) 			69.0.3497.100	Green
Macbook Air Early 2015 (13-inch, HD Graphics 6000) 		69.0.3497.100	Green
Macbook Pro 2016 (13-inch, Iris Graphics 550) 			69.0.3497.100	Green
Macbook Pro 2018 (15-inch, UHD Graphics 630) 			69.0.3497.100	Green

Hm... Do we have different workarounds on that device in particular? Or is it a hardware/driver bug on Iris Pro only, that Chrome happens to hit because it does something else differently from the other browsers?

Could someone please also contribute a WebGL conformance test to https://github.com/KhronosGroup/WebGL – perhaps under conformance/rendering – that catches this alpha blending error? It looks like RGB textures are broken on this driver. Thanks.

I have written a conformance test based on the case provided here:
https://github.com/KhronosGroup/WebGL/pull/2716

Shall we write a Radar about this issue to Apple?

Yes, please. Would you mind writing a draft? Thanks.

Conformance test has been integrated here:
https://www.khronos.org/registry/webgl/sdk/tests/conformance/rendering/canvas-alpha-bug.html

Thanks Jiawei for writing the conformance test and text for the Radar. Filed Radar 45235525 about it.

Submitter, I recommend you allocate RGBA instead of RGB textures as a workaround. We would prefer to not work around this bug in the browser; it will be a lot of code for one particular GPU type on macOS, and hopefully Apple and Intel will collaborate to fix it.

I believe is a chromium/angle bug on working with alpha channel on frame buffers, in our product we have more strangle result with invalid alpha-channel values at any GPU, (Chrome only): Transparent canvas on each 3-th frame (on canvas configured without alpha), but reproduce on POC code too hard. For now we use workaround: clean alpha channel on end of frame.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/319faa6f9fc6bb050759c111202dbb61ba99086d

commit 319faa6f9fc6bb050759c111202dbb61ba99086d
Author: Kenneth Russell <kbr@chromium.org>
Date: Wed Oct 24 17:21:44 2018

Roll WebGL 6d2f3f4..0d55c88

https://chromium.googlesource.com/external/khronosgroup/webgl.git/+log/6d2f3f4..0d55c88

Includes suppressions for the following failures:

  conformance/rendering/rendering-sampling-feedback-loop.html
  conformance2/textures/misc/tex-mipmap-levels.html
  conformance2/textures/image_bitmap_from_video/
    tex-2d-rgb565-rgb-unsigned_short_5_6_5.html
  deqp/functional/gles3/lifetime.html
  deqp/functional/gles3/shaderoperator/common_functions_*.html

Bug: 660844,  739604 , 766918, 849576, 886970,  890002 , 890539,  898350 ,  898351 ,  angleproject:2832 
Cq-Include-Trybots: luci.chromium.try:win_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_angle_rel_ng;luci.chromium.try:win_angle_rel_ng
Change-Id: I85be441fa86090e5ed056a9366452248985693e3
Reviewed-on: https://chromium-review.googlesource.com/c/1297570
Reviewed-by: James Darpinian <jdarpinian@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602377}
[modify] https://crrev.com/319faa6f9fc6bb050759c111202dbb61ba99086d/DEPS
[modify] https://crrev.com/319faa6f9fc6bb050759c111202dbb61ba99086d/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py
[modify] https://crrev.com/319faa6f9fc6bb050759c111202dbb61ba99086d/content/test/gpu/gpu_tests/webgl_conformance_expectations.py
[modify] https://crrev.com/319faa6f9fc6bb050759c111202dbb61ba99086d/content/test/gpu/gpu_tests/webgl_conformance_revision.txt

More information: it's a regression in the Mac OpenGL driver for Haswell GPUs in 10.13. The test passes on 10.12. A suppression for the failure on 10.13 is incoming.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/629399230ca1367b962a2dfa89b89c4a95ede1ee

commit 629399230ca1367b962a2dfa89b89c4a95ede1ee
Author: Kenneth Russell <kbr@chromium.org>
Date: Wed Oct 24 22:09:21 2018

Suppress canvas-alpha-bug failure on Mac Intel Haswell GPUs.

conformance/rendering/canvas-alpha-bug.html is failing on this
configuration on 10.13 and later. Rather than specialize the
suppression for multiple OS versions, suppress it on this GPU type.

Tbr: jdarpinian@chromium.org
No-Try: True
Bug: 886970
Change-Id: Ifeeaa59aca1c232b3d3eda6b2a82b35451c8a2bc
Reviewed-on: https://chromium-review.googlesource.com/c/1298199
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602479}
[modify] https://crrev.com/629399230ca1367b962a2dfa89b89c4a95ede1ee/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py
[modify] https://crrev.com/629399230ca1367b962a2dfa89b89c4a95ede1ee/content/test/gpu/gpu_tests/webgl_conformance_expectations.py

Square is red

MacBook PRO, Late 2013 A1502 (13-inch, Intel Iris Graphics 6100) 10.14.1

Square is BLUE

iMac (27-inch, Mid 2010) ATI Radeon HD 5750 1024MB 
MacOS 10.11.6
Chrome 71.0.3578.80