This talk will cover our experience in utilizing Wayland subsurfaces and implementing delegated compositing for Chromium on ChromeOS. Several concepts will be covered - from overlay making decision in Chromium/Viz to design and implementation of custom Wayland protocols, which were required to pass frame data as overlays via Wayland and reconstruct that frame on the Wayland server side. (c) FOSDEM 2024 3 & 4 February 2024 https://fosdem.org/2024/schedule/event/fosdem-2024-3177-delegated-compositing-utilizing-wayland-protocols-for-chromium-on-chromeos/

1. Delegated Compositing -
Utilizing Wayland Protocols
for Chromium on ChromeOS
Maksim Sisov - msisov@igalia.com
Fosdem 2024 - 04/02/2024
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2. Agenda
Chromium/Wayland in ChromeOS - Goals and
Motivation
What is LaCrOS?
Chromium Display Compositor
Delegated Compositing
Wayland Protocols
A Big Picture
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3. Chromium/Wayland
in ChromeOS
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4. Goals and Motivation
Improve maintainability
Let more users receive
browser updates (old
devices)
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5. How?
Decouple the browser from OS (LaCrOS project)
ChromeOS (system UI and Ash Window Manager)
and Chrome are tied together
Use Wayland
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6. Why Wayland?
ChromeOS has a Wayland server implementation
called exosphere
Used by ARC (Android apps) and Crostini (Linux
apps)
Chromium is a Wayland client
Use Wayland for graphics and event handling
Stable Wayland protocols and custom extensions
Use crosapi (Mojo IPC) for higher-level features
(e.g. file picking)
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7. What is LaCrOS?
A project to decouple the
Chrome Browser from
the ChromeOS Window
Manager (Ash) and
System UI
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8. This split results in performance/resource cost.
Why?
How to mitigate that?
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9. Chromium Display
Compositor
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12. Double compositing and
bigger resources overhead
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13. How to Fix That?
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14. Delegated Compositing
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15. Wayland Protocols
wl_subsurface - Each quad/overlay is represented by
own surface
wl_buffer - Can be attached to multiple subsurfaces
linux_explicit_synchronization - Fence for each
quad's buffer
Additional protocols:
surface-augmenter - extending wl_surface
(rounded corners and clipping, pixel precision)
single-pixel-buffer - for color buffers
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16. surface-augmenter
wl_subsurface::set_position
wp_viewport::set_destination
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17. augmented_sub_surface::set_position(augmented_surface,
wl_fixed_t, wl_fixed_t)
augmented_surface::set_destination_size(augmented_surface
wl_fixed_t, wl_fixed_t)
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18. augmented_surface::set_transform
augmented_surface::set_trusted_damage
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20. Thank you
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