class LinkSystem

Creates the parent end of a link. The LinkToChild's |internal_link_handle| serves as the

attachment point for the caller's transform hierarchy. |initial_properties| is immediately

dispatched to the LinkToParent when the Link is resolved, regardless of whether the parent or

the child has called |Flatland::Present()|.

Link handles are excluded from global topologies, so the |parent_transform_handle| is

provided by the parent as the attachment point for the ChildViewWatcherImpl.

|dispatcher_holder| allows hanging-get response-callbacks to be invoked from the appropriate

Flatland session thread.

Creates the child end of a link. Once both ends of a Link have been created, the LinkSystem

will create a local topology that connects the internal Link to the LinkToParent's

|child_transform_handle|.

|dispatcher_holder| allows hanging-get response-callbacks to be invoked from the appropriate

Flatland session thread.

Because this object captures its "this" pointer in internal closures, it is unsafe to copy or

move it. Disable all copy and move operations.

Populates `out_links` with a snapshot of the current set of links, represented as a map from

LinkSystem-owned TransformHandles to TransformHandles in LinkToParents, and returns the

`link_topology_generation_` value the snapshot was taken at. The LinkSystem generates Keys for

this map in CreateLinkToChild() and returns them to callers in a LinkToChild's

`internal_link_handle`. The values in this map are arguments to CreateLinkToParent() and become

the LinkToParent's `child_transform_handle`. The LinkSystem places entries in the map when a

link resolves and removes them when a link is invalidated.

Like `GetResolvedTopologyLinks()`, but leaves `out_links` untouched when the generation equals

`known_generation`, so a caller that still holds the links of that generation skips the copy.

Returns the instance ID used for LinkSystem-authored handles.

For use by the core processing loop, this function consumes global information, processes it,

and sends all necessary updates to active ParentViewportWatcher and ChildViewWatcher channels.

This data passed into this function is generated by merging information from multiple Flatland

instances. |global_topology| is the TopologyVector of all nodes visible from the (currently

single) display. |live_handles| is the set of nodes in that vector. |global_matrices| is the

list of global matrices, one per handle in |global_topology|. |uber_structs| is the set of

UberStructs used to generate the global topology.

Populates `out_map` with the mapping from the `child_transform_handle` of each LinkToParent to

the corresponding `parent_transform_handle` from each LinkToChild.

Updates |device_pixel_ratio_| for the View with parent |handle|. If the value changed it sends

updates to all waiting clients, otherwise it does nothing.

|handle| should have been previously used as |parent_transform_handle| in CreateLinkToChild().

Updates |device_pixel_ratio_| and, if the value changed, sends updates to all waiting clients.