+varkha@.

Continue the discussion in the cl:
When entering overview mode, we only call transform_window_.SetTransform [1] so there is no opacity animation, so no render surface.
When existing overview mode, we do call additional SetOpacity [2], so we have opacity in the animation. Therefore we created the render surface?

[1] https://cs.chromium.org/chromium/src/ash/wm/overview/window_selector_item.cc?l=677&rcl=65c8da95cbc89501e08ba28cd3bc9d308f20a026
[2] https://cs.chromium.org/chromium/src/ash/wm/overview/scoped_transform_overview_window.cc?l=197&rcl=6239bc6b7d27a33b9498fb237dd8a0553cfe3362

#2, removed the SetOpacity here [1], can remove the render surface when exiting overview mode.
And seems the SetOpacity does not do anything.

[1] https://cs.chromium.org/chromium/src/ash/wm/overview/scoped_transform_overview_window.cc?l=197&rcl=6239bc6b7d27a33b9498fb237dd8a0553cfe3362

I do see huge improvement by just cache the render surface during animation:

5 browser windows, 30x slow-down-compositiong-scale-factor=30
Linux builds: ~55%

On Kevin, I must use long animation duration (10s) to see ~15% improvement.

Does it still properly dim the items other than selected when text filter is on?

#4, that's nice, what do the improvement numbers mean?

#5, thanks, I see this SetOpacity for now. The caching render surface does not need to remove the code of SetOpacity.

#6, sorry for the confusion. The numbers are:
When I tested overview mode animation in linux builds, I opened 5 blank browsers, and to repeatedly draw render surface 30 times (which is to simulate slower machine), the mean of histogram Ash.WindowSelector.AnimationSmoothness.Enter was improved from 55% to 85%, about ~55% improvement.

We plan to turn on render surface caching and trilinear filtering in overview mode at the same time.

The difficulty part is that to keep caching and filtering all there phases during overview mode: 1) entering animation, 2) staying in the overview mode, 3) exiting animation.

There seems no single place we can add and remove the caching and filtering requests. But what we can do is do it multiple times: 1) + 2) can be achieved add/remove requests in ScopedTransformOverviewWindow::PrepareForOverview/RestoreWindow. For 3), we can add/remove requests on beginning/ending of the exiting animation.

I wonder should we make the ui::Layer::SetTrilinearFiltering API similar to ui::Layer::AddCacheRenderSurfaceRequest with a request counter. And add rilinearFilteringObserver in scoped layer animation settings similar to RenderSurfaceObserver?

Add/Remove API is fine with me if that's the best solution here too.

Maybe we make it a little complicated to Add/Remove trilinear request API. But just in case multiple places (and/or animations) try to set/unset the trilinear filtering on the same layer.

The trilinear filtering results look terrific!
Thanks reveman@!

Deleted: without_trilinear_filtering.png 1.1 MB

	without_trilinear_filtering.png 1.1 MB View Download

Deleted: with_trilinear_filtering.png 1.1 MB

	with_trilinear_filtering.png 1.1 MB View Download

Uploaded a cl to: https://chromium-review.googlesource.com/c/chromium/src/+/717725

I had limited number of tests on how much the caching render surface + defer painting combination can improve the overview animation smoothness.

On linux build (Z840), --slow-down-compositing-scale-factor=30, with 5 blank chrome browsers with maximized size. The 10 times of average results are about:
~33% improvement for enter animation.
~48% improvement for exit animation.
Those number might be very different than real device and are different than in the comment of #7. UMA will let us know the real improvement later.

Details are:
enter/exit animation smoothness (%, 100% is ideal frame per second)

1. Current ToT code:                                       48.2%/41.2%
2. DeferPaint:                                             54.9%/43.0%
3. TrilinearFiltering:                                     45.8%/37.6%
4. DeferPaint + TrilinearFiltering:                        52.4%/38.4%
5. CachingRenderSurface:                                   52.4%/50.8%
6. TrilinearFiltering + CachingRenderSurface:              54/1%/50.0%
7. DeferPaint + CachingRenderSurface:                      65.3%/59.9%
8. DeferPaint + TrilinearFiltering + CachingRenderSurface: 64.2%/61.0%

Really exciting to see all this come together! If we could get mipmaps and caching turned on for window switcher as well in M63 that would be awesome!

Btw, we have one level of fullscreen overdraw in overview mode just because we dim the background using a solid color layer with opacity. I think we should switch that to setting brightness for the wallpaper layer instead and make sure the compositor implements that efficiently. We can probably use the color matrix like we're looking at doing for the night mode color temperature effect.

# 19, sg! I will work on the wallpaper dimmer.

#19, created other two issues for:
Wallpaper dimmer in overview mode:
https://bugs.chromium.org/p/chromium/issues/detail?id=774690

Using mipmaps and caching turned on for window switcher:
https://bugs.chromium.org/p/chromium/issues/detail?id=773841

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2a577cfa8d7c87946f9335fe5ee831b322da7fda

commit 2a577cfa8d7c87946f9335fe5ee831b322da7fda
Author: wutao <wutao@chromium.org>
Date: Tue Oct 17 01:05:59 2017

Use trilinear filtering and Cache render surface in overview mode.

To get better image quality when we are scaling down windows in overview
mode, we can apply the trilinear filtering. At the same time we cache
the render surface for good performance and reduced overdraw.

without trilinear filtering:
with trilinear filtering:

Bug:  756696 
Test: Tested local
Change-Id: I12765172efec921c9336b32f0aa3fa8ba7e78f35
Screenshot: 
https: //screenshot.googleplex.com/MYU3w3ff6s0
https: //screenshot.googleplex.com/AqGiVp4eh43
Reviewed-on: https://chromium-review.googlesource.com/717725
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Valery Arkhangorodsky <varkha@chromium.org>
Reviewed-by: David Reveman <reveman@chromium.org>
Commit-Queue: Tao Wu <wutao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509198}
[modify] https://crrev.com/2a577cfa8d7c87946f9335fe5ee831b322da7fda/ash/wm/overview/scoped_overview_animation_settings.cc
[modify] https://crrev.com/2a577cfa8d7c87946f9335fe5ee831b322da7fda/ash/wm/overview/scoped_overview_animation_settings.h
[modify] https://crrev.com/2a577cfa8d7c87946f9335fe5ee831b322da7fda/ash/wm/overview/scoped_transform_overview_window.cc
[modify] https://crrev.com/2a577cfa8d7c87946f9335fe5ee831b322da7fda/ash/wm/overview/scoped_transform_overview_window.h
[modify] https://crrev.com/2a577cfa8d7c87946f9335fe5ee831b322da7fda/testing/buildbot/filters/ash_unittests_mash.filter
[modify] https://crrev.com/2a577cfa8d7c87946f9335fe5ee831b322da7fda/testing/buildbot/filters/ash_unittests_mus.filter

Your change meets the bar and is auto-approved for M63. Please go ahead and merge the CL to branch 3239 manually. Please contact milestone owner if you have questions.
Owners: cmasso@(Android), cmasso@(iOS), gkihumba@(ChromeOS), govind@(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/+/c4567563e222638c0d3c3f6d80be808614f34b7d

commit c4567563e222638c0d3c3f6d80be808614f34b7d
Author: wutao <wutao@chromium.org>
Date: Wed Oct 18 01:47:27 2017

[Merge M63] Use trilinear filtering and Cache render surface in overview mode.

To get better image quality when we are scaling down windows in overview
mode, we can apply the trilinear filtering. At the same time we cache
the render surface for good performance and reduced overdraw.

TBR=reveman@chromium.org,varkha@chromium.org

Bug:  756696 
Test: Tested local
Change-Id: I12765172efec921c9336b32f0aa3fa8ba7e78f35
Screenshot: 
https: //screenshot.googleplex.com/MYU3w3ff6s0
https: //screenshot.googleplex.com/AqGiVp4eh43
Reviewed-on: https://chromium-review.googlesource.com/717725
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Valery Arkhangorodsky <varkha@chromium.org>
Reviewed-by: David Reveman <reveman@chromium.org>
Commit-Queue: Tao Wu <wutao@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#509198}(cherry picked from commit 2a577cfa8d7c87946f9335fe5ee831b322da7fda)
Reviewed-on: https://chromium-review.googlesource.com/724740
Reviewed-by: Tao Wu <wutao@chromium.org>
Cr-Commit-Position: refs/branch-heads/3239@{#42}
Cr-Branched-From: adb61db19020ed8ecee5e91b1a0ea4c924ae2988-refs/heads/master@{#508578}
[modify] https://crrev.com/c4567563e222638c0d3c3f6d80be808614f34b7d/ash/wm/overview/scoped_overview_animation_settings.cc
[modify] https://crrev.com/c4567563e222638c0d3c3f6d80be808614f34b7d/ash/wm/overview/scoped_overview_animation_settings.h
[modify] https://crrev.com/c4567563e222638c0d3c3f6d80be808614f34b7d/ash/wm/overview/scoped_transform_overview_window.cc
[modify] https://crrev.com/c4567563e222638c0d3c3f6d80be808614f34b7d/ash/wm/overview/scoped_transform_overview_window.h
[modify] https://crrev.com/c4567563e222638c0d3c3f6d80be808614f34b7d/testing/buildbot/filters/ash_unittests_mash.filter
[modify] https://crrev.com/c4567563e222638c0d3c3f6d80be808614f34b7d/testing/buildbot/filters/ash_unittests_mus.filter