046f987e02
See this doc: go/chromium-coil-change for more info
BUG=1210385
Change-Id: I6cd8548301e360bae8e71384dbd8ef11aa6c985f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2902904
Reviewed-by: My Nguyen <myy@chromium.org>
Commit-Queue: My Nguyen <myy@chromium.org>
Auto-Submit: John Palmer <jopalmer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#885851}
70 lines
4.9 KiB
Markdown
70 lines
4.9 KiB
Markdown
# Windows 10 Virtual Desktop support
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Windows 10 introduced Virtual Desktop support. Virtual Desktops are similar to
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Chrome OS and Mac workspaces. A virtual desktop is a collection of windows.
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Every window belongs to a virtual desktop. When a virtual desktop is selected
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to be active, the windows associated with that virtual desktop are displayed on
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the screen. When a virtual desktop is hidden, all of its windows are also
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hidden. This enables the user to create multiple working environments and to
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switch between them. An app (e.g., Chromium) can have windows open on
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different virtual desktops, and thus may need to be Virtual Desktop-aware.
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The user-facing Chromium support for virtual desktops consists of two things:
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* When launching the browser with session restore, browser windows are moved
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to the virtual desktop they were on when the browser shutdown.
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* When opening a URL with the browser, either open it in a window on the
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current virtual desktop, or open a new window on the current virtual desktop.
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Don't open it in a tab in a window on another virtual desktop.
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The core UI principles are that windows should be restored to the desktop they
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were shut down on, and opening an app window shouldn't change the current
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virtual desktop. Only the user should be able to change virtual desktops, or
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move windows between virtual desktops.
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Windows 10 exposes the COM interface
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[IVirtualDesktopManager](https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nn-shobjidl_core-ivirtualdesktopmanager)
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to access the Virtual Desktop functionality. To make sure that opening a URL
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stays on the current virtual desktop,
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[BrowserView::IsOnCurrentWorkspace](https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/ui/views/frame/browser_view.cc?q=%20BrowserView::IsOnCurrentWorkspace)
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uses the IVirtualDesktopManager method
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[IsWindowOnCurrentVirtualDesktop](https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-ivirtualdesktopmanager-iswindowoncurrentvirtualdesktop).
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[BrowserMatches](https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/ui/browser_finder.cc?q=BrowserMatches)
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in browser_finder.cc only returns a browser window on the current desktop.
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To restore browser windows to the desktop they were last open on,
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[BrowserDesktopWindowTreeHostWin](https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc)
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implements GetWorkspace by using the
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[GetWindowDesktopId](https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-ivirtualdesktopmanager-getwindowdesktopid) method on
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IVirtualDesktopManager, and restores the workspace using
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[MoveWindowToDesktop](https://docs.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-ivirtualdesktopmanager-movewindowtodesktop),
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in its ::Init method.
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The actual implementation is a bit more complicated in order to avoid
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calling COM methods on the UI thread, or destroying COM objects on the UI
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thread, since doing so can cause nested message loops and re-entrant calls,
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leading to blocked UI threads and crashes. The
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[VirtualDesktopHelper](https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc?q=VirtualDesktopHelper&sq=&ss=chromium%2Fchromium%2Fsrc)
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class does the workspace handling for BrowserDesktopWindowTreeHostWin, including
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doing all the COM operations on a separate COM task runner. The GetWorkspace
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method is synchronous so VirtualDesktopHelper has to remember and return the
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most recent virtual desktop. Windows has no notification of a window changing
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virtual desktops, so BrowserDesktopWindowTreeHostWin updates the virtual desktop
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of a window whenever it gets focus, and if it has changed, calls
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WindowTreeHost::OnHostWorkspaceChanged. This means that if a window is moved
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to a different virtual desktop, but doesn't get focus before the browser is shut
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down, the browser window will be restored to the previous virtual desktop.
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Windows on different virtual desktops share the same coordinate system, so code
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that iterates over windows generally needs to be Virtual Desktop-aware.
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For example, the following places in code ignore windows not on the current
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virtual desktop:
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* [LocalProcessWindowFinder::GetProcessWindowAtPoint](https://source.chromium.org/chromium/chromium/src/+/main:ui/display/win/local_process_window_finder_win.cc?q=LocalProcessWindowFinder::ShouldStopIterating&ss=chromium%2Fchromium%2Fsrc)
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* third_party/webrtc/modules/desktop_capture/win/window_capture_utils.cc
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* [Native Window occlusion tracker](https://source.chromium.org/chromium/chromium/src/+/main:ui/aura/native_window_occlusion_tracker_win.cc?q=WindowCanOccludeOtherWindowsOnCurrentVirtualDesktop&ss=chromium%2Fchromium%2Fsrc),
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when determining if a Chromium window is occluded/covered by other windows.
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Windows not on the current virtual desktop are considered occluded.
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