construct::rendering::ViewportFeed Class

Detailed Description

A worker viewport draws from data, never from the live model. A structural edit hands it a whole ConstructSnapshot, and a parameter edit hands it a WorkerSceneDelta that it applies in place with nothing compiled (construct-scene-evaluator §EV-A3). The feed decides which of the two an edit needs. It also turns a burst of edits into one hand-off per event-loop turn, numbers the snapshots, and turns a delta into a snapshot when a delta cannot carry the change.

These rules are the same for every worker viewport. They were members of ConstructShell until the definition editor's preview needed the same rules (construct-multi-document MD-38), so both use this class now.

The rules:

• scheduleSnapshot() and scheduleDelta() coalesce. All calls in one turn leave as one snapshot, or as one delta that names every changed item.
• A snapshot carries every value. It drops the pending delta ids, and a delta queued in the same turn as a snapshot is not sent.
• Each snapshot gets the next structure version. A delta names the version that it applies to, and the worker drops a delta for a scene that it does not have.
• An item whose out-of-band payload changed (a mesh soup, a tet mesh, a proxy version, see Hooks::payloadIdentity) causes a snapshot, because a delta carries no payloads.
• A document with items that gives an empty snapshot is a defect. The previous scene stays on screen and is not blanked.

What differs per client is in Hooks: where the viewport and the document are, how the snapshot is built, and how an item is prepared for the worker. hooksFor() gives the plain answers.

GUI thread only.