2D canvas contexts started publishing partial frames after canvas
rasterization moved into the Compositor. WebContent still splits large
recorded command lists after 64 commands, but every split batch was sent
through the same compositor path as the end-of-frame flush. The
compositor replayed each batch into the DrawCanvas source surface,
so a pending present could sample a canvas after clear and before the
rest of the next frame had been drawn. Canvas-heavy pages such as
slither.com then flickered between partial and complete frames.
Carry an explicit commit bit with 2D canvas command updates. Non-commit
batches now update a hidden working canvas in the Compositor, while the
display-list-visible surface keeps the last committed canvas contents.
The end-of-frame canvas preparation sends the commit boundary, including
the empty-commit case needed when the auto-flush consumed all recorded
commands before prepare_for_compositing() runs.
Nested navigables were represented through compositor surface ids owned
by the parent context. That forced CompositorState and ContextState to
maintain bidirectional attach/detach bookkeeping, publish child
snapshots into a surface map, and keep presentation mode variants just
to distinguish UI presentation from parent composition.
Record the child compositor context id directly in the display list and
let the compositor resolve it against the painting parent at playback
time. Child contexts now keep their parent context id and latest
rendered surface, while parents no longer track child maps or compositor
surface ids. UI presentation is represented separately from parent
composition, so closing a page only stops client presentation and nested
contexts keep using set_parent_context.
Compositor surfaces are only used for nested navigables now. The
display list command already carries the CompositorSurfaceId, but
playback still resolved that id through DisplayListResourceStorage and
WebContent exposed IPC for direct surface updates and clears.
Keep published child surfaces as PaintingSurface entries on the
compositor ContextState and pass that map into Skia display list
playback. Publishing and detaching nested contexts now update the parent
cache entirely inside the compositor, so WebContent no longer needs
update_compositor_surface or clear_compositor_surface messages.
The display list can now refer to canvas ids, but WebContent still had
no channel for creating or updating those canvas resources in the
Compositor. Both 2D and WebGL canvases would have had to grow the IPC
plumbing in the same commit that changes the rendering contexts.
This adds the Compositor-side CanvasHost, WebContent transport objects,
and the IPC/CMake pieces needed to allocate, update, read back, and
destroy remote canvas contexts. The rendering contexts are not switched
over yet, keeping this as plumbing for later commits.
A WebContent display-list update can send compositor resource
attachments over the WebContent-to-compositor transport. On Windows,
serializing an attachment requires the destination process id, but this
secondary transport never exchanged peer pids before the first message.
That left TransportSocketWindows with m_peer_pid == -1 and hit the
serialize_attachments() verification when WebContent tried to send the
first attachment-bearing compositor update. Add InitTransport to this
endpoint and run it immediately after WebContent creates the compositor
connection, before any other IPC uses the channel.
Display list updates already ship their compatible accumulated visual
context tree to the compositor, but there was no way to replace only the
tree for an existing display list. That kept any visual-context-only
change tied to a full display list update.
Add an update_visual_context_tree IPC path from WebContent through the
Compositor service. ContextState validates that the incoming tree
matches the installed display list's compatible tree version and
rebuilds wheel hit-test targets when async scrolling state is present.
CompositorState treats presence in m_contexts as the lifetime state
for a compositor context. create_context() creates the entry and
destroy_context() removes it, so ContextState::is_registered duplicated
the map membership invariant.
The top-level-traversable bit was also duplicate information. The
only compositor use was backing-store padding while a window resize is
in progress, and page-presenting contexts are already identified by
PagePresentationRegistration::Yes. Normalize resize-in-progress to No
for non-page-presenting contexts, then remove the flag from
CompositorState, the backing-store API, and the compositor IPC boundary.
Display lists owned the accumulated visual context tree through a
ref-counted pointer. That tied visual-context state to display-list
lifetime and made compositor updates treat the two as one unit, even
though AVC trees need to become independently updateable compositor
state.
Make accumulated visual context trees plain versioned values, have each
display list store the compatible tree version, and pass the matching
tree alongside display-list updates and replay calls. Replay verifies
that the provided tree matches the display list before executing it.
This prepares the compositor for receiving AVC tree updates separately
from display-list updates: it now accepts the tree as a separate update
parameter, stores it next to the display list, and uses that stored tree
for replay and async-scroll hit testing. Nested display-list resources
carry their own tree snapshots for the same version check.
The WebContent compositor server exposed stop_presenting_to_client()
next to destroy_context(), even though only the latter controls context
lifetime. The former moved a live top-level context out of the client-
facing presentation path, making the IPC boundary look like it had two
ways to tear down a live compositor context.
Make client presentation an explicit PresentationMode alternative.
Top-level contexts start as PresentToClient. Tab close switches them to
Empty, while destroy_context() remains the only API that removes
compositor state. This keeps the existing lifetime behavior while
routing all presentation target changes through set_presentation_mode().
With CompositorState in place, Browser and WebContent need an actual
wire protocol to drive it: which calls are sync, who validates that a
WebContent is allowed to touch a given context, how compositor loss
propagates back to the renderer. This commit fills in the four endpoints
around CompositorState and the matching WebContent-side helpers so the
future remote host can forward CompositorHost calls directly. The
service still has no clients, so default rendering is unchanged.
The compositor is moving into a dedicated helper process. That requires
a process to launch, channels for Browser and WebContent to talk to it
over, and client proxies on each side. Land all of that as an inert
scaffold first, gated behind --enable-compositor-process, so the default
rendering path is unchanged and later commits can fill in the protocol,
the service-side state, and the runtime switch against a stable target.
