+omrilio who also reported this issue to me.

Nice catch, thank you!

Is there a way to repro this in the Ozone/sandbox thing? Shelf auto-hiding doesn't seen to do anything there. Are there flags I'm missing?

I believe you have to open a window to make the shelf actually hide. This should work in the emulator but I haven't tried. Maybe minch@ knows!

re #3, yes, we need to have a visible window to make shelf actually hide. I can repro this in the emulator. It will be more obviously if add --ui-slow-animations in your build.
Sorry I don't have too much thought about the blur part, seems that there is no animation for the blur of the shelf. I guess wutao@ might have more knowledge for blur.

When blur is applied, it will appear in the next frame.
Unless you set blur radius progressively when the Shelf becomes visible.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c5990315053b5d925c5ce4bcb4332df9cc9e95e2

commit c5990315053b5d925c5ce4bcb4332df9cc9e95e2
Author: Manu Cornet <manucornet@chromium.org>
Date: Tue Sep 11 08:06:03 2018

CrOS Shelf: enable bg blur only when app list blue is on

Enable shelf background blur only when the launcher's background
blur is enabled.

This allows for a more consistent user experience, and may also
help with performance on some devices.

Bug: 879962,881134
Change-Id: I40015199f3312b62ef7b175167b65d5a9a6e352a
Reviewed-on: https://chromium-review.googlesource.com/1217584
Commit-Queue: Manu Cornet <manucornet@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590230}
[modify] https://crrev.com/c5990315053b5d925c5ce4bcb4332df9cc9e95e2/ash/shelf/shelf_layout_manager.h
[modify] https://crrev.com/c5990315053b5d925c5ce4bcb4332df9cc9e95e2/ash/shelf/shelf_widget.cc

Updating description to also mention corner glitch, which I think come from the same issue.

 Issue 882150  has been merged into this issue.

Ok, after a lot of trial and error to try to figure this out, it seems like this is a problem coming from the interaction between blur and opacity.

The shelf's opacity increases from 0 to 1 as it animates from being hidden to being shown. Apparently the blur doesn't want to take effect on a partially transparent layer.

So even if I update the blur radius during the animation, no blur actually happens until the animation is over and the shelf is opaque.

Adding Mitsuru who will probably have a lot of insights on this. :-)

 Issue 882029  has been merged into this issue.

This is a little bit of a hairy problem with animation, layers and masks that I haven't quite figured out yet. It will likely take some more time, and I may want to change the current model of shelf auto-hide animation (animate position instead of height). I think it's safer to punt this to M-71.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/15020b8f5d62bd73aa871b2fa50f1ccee4c37125

commit 15020b8f5d62bd73aa871b2fa50f1ccee4c37125
Author: Manu Cornet <manucornet@chromium.org>
Date: Wed Sep 19 15:22:33 2018

CrOS Shelf: Set background blur only once

This does not fix any known issues (and in fact doesn't change any
behavior), but it seems wasteful to set the background blur to the
exact same value multiple times.

Bug: 881134
Change-Id: I3762c486385d9136f1aea3e50d1e304d69aef141
Reviewed-on: https://chromium-review.googlesource.com/1233122
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Manu Cornet <manucornet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592408}
[modify] https://crrev.com/15020b8f5d62bd73aa871b2fa50f1ccee4c37125/ash/shelf/shelf_widget.cc

This bug requires manual review: M70 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: benmason@(Android), kariahda@(iOS), geohsu@(ChromeOS), abdulsyed@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b23fbb63c5179016e33cafc87edaeb5c81a0cfe6

commit b23fbb63c5179016e33cafc87edaeb5c81a0cfe6
Author: Manu Cornet <manucornet@chromium.org>
Date: Sat Sep 22 02:39:16 2018

CrOS Shelf: enable bg blur only when app list blue is on

Enable shelf background blur only when the launcher's background
blur is enabled.

This allows for a more consistent user experience, and may also
help with performance on some devices.

Bug: 879962,881134
Change-Id: I40015199f3312b62ef7b175167b65d5a9a6e352a
Reviewed-on: https://chromium-review.googlesource.com/1217584
Commit-Queue: Manu Cornet <manucornet@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#590230}(cherry picked from commit c5990315053b5d925c5ce4bcb4332df9cc9e95e2)
Reviewed-on: https://chromium-review.googlesource.com/1239295
Reviewed-by: Manu Cornet <manucornet@chromium.org>
Cr-Commit-Position: refs/branch-heads/3538@{#581}
Cr-Branched-From: 79f7c91a2b2a2932cd447fa6f865cb6662fa8fa6-refs/heads/master@{#587811}
[modify] https://crrev.com/b23fbb63c5179016e33cafc87edaeb5c81a0cfe6/ash/shelf/shelf_layout_manager.h
[modify] https://crrev.com/b23fbb63c5179016e33cafc87edaeb5c81a0cfe6/ash/shelf/shelf_widget.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/429731975a4d5b6dea20eaf9eab9296195f5418a

commit 429731975a4d5b6dea20eaf9eab9296195f5418a
Author: Manu Cornet <manucornet@chromium.org>
Date: Mon Sep 24 21:18:48 2018

CrOS Shelf: Set background blur only once

This does not fix any known issues (and in fact doesn't change any
behavior), but it seems wasteful to set the background blur to the
exact same value multiple times.

Bug: 881134
Change-Id: I3762c486385d9136f1aea3e50d1e304d69aef141
Reviewed-on: https://chromium-review.googlesource.com/1233122
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Manu Cornet <manucornet@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#592408}(cherry picked from commit 15020b8f5d62bd73aa871b2fa50f1ccee4c37125)
Reviewed-on: https://chromium-review.googlesource.com/1241560
Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Cr-Commit-Position: refs/branch-heads/3538@{#601}
Cr-Branched-From: 79f7c91a2b2a2932cd447fa6f865cb6662fa8fa6-refs/heads/master@{#587811}
[modify] https://crrev.com/429731975a4d5b6dea20eaf9eab9296195f5418a/ash/shelf/shelf_widget.cc

The following revision refers to this bug: 
https://chromium.googlesource.com/chromium/src.git/+/429731975a4d5b6dea20eaf9eab9296195f5418a

Commit: 429731975a4d5b6dea20eaf9eab9296195f5418a
Author: manucornet@chromium.org
Commiter: newcomer@chromium.org
Date: 2018-09-24 21:18:48 +0000 UTC

CrOS Shelf: Set background blur only once

This does not fix any known issues (and in fact doesn't change any
behavior), but it seems wasteful to set the background blur to the
exact same value multiple times.

Bug: 881134
Change-Id: I3762c486385d9136f1aea3e50d1e304d69aef141
Reviewed-on: https://chromium-review.googlesource.com/1233122
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Manu Cornet <manucornet@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#592408}(cherry picked from commit 15020b8f5d62bd73aa871b2fa50f1ccee4c37125)
Reviewed-on: https://chromium-review.googlesource.com/1241560
Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Cr-Commit-Position: refs/branch-heads/3538@{#601}
Cr-Branched-From: 79f7c91a2b2a2932cd447fa6f865cb6662fa8fa6-refs/heads/master@{#587811}

I still found this issue with 71.0.3565.0 OS, could I which OS version fix this issue?

 Issue 895534  has been merged into this issue.

All, this continues to be an issue - and will be seen by users on M-71.
We also have a few devices FSI-ing on M-71. Will this be fixed in M71 ?

Assign this myself. Working on a fix now.

I uploaded a testing cl to [1].
This cl has not fixed all the things yet. Just approve that during animation the blur can be applied.
[1] https://chromium-review.googlesource.com/c/chromium/src/+/1299698


Due to the urgent and complexity of this bug, assign it back to the Shelf expert.

I'm trying to do this in a slightly simpler way. Current CL is at:

    https://chromium-review.googlesource.com/c/chromium/src/+/1300691

And I'm attaching a screencast. I think this looks good.

Deleted: shelf_blur.mp4 1.6 MB

	shelf_blur.mp4 1.6 MB View Download

Ok there's been a few attempts at these and it's harder than it looks because of all the mask/layer/opacity/blur stuff. I think it's wise to spend some time understanding and sanitizing all that in time for M-72 rather than rush something. Still debating whether this is bad enough to really need a fix in M-71, but I'm thinking it would be wise to do all this more calmly.

FYI trying to simplify the layer structure and hopefully get to the bottom of this. Pending CL 1344997

Bulk moving <p-1's to the next milestone because we branched to M-73.

Issue 917609 has been merged into this issue.