Linking Scripts

These scripts contain all the logic for creating links between nodes. This involves, to a large extent, deciding which links to create.

Hooks

The hooks in this section are organized in 3 sub-categories. The first category includes hooks that are triggered by changes in the graph. Some of them are tasked to schedule a “rescan-for-linking” event, which is the lowest priority event and its purpose is to scan through all the linkable session items and link them to a particular target. The “rescan-for-linking” event is always scheduled to run once for all the graph changes in a cycle. This is achieved by flagging the event as already scheduled in the module-standard-event-source; this flag is then cleared by a hook that runs on this event.

Selecting a target for each linkable and linking to it is deferred to another set of hooks by pushing a “select-target” event for each linkable. This event is the highest priority event and therefore no other changes in the graph are processed while targets are being selected.

Hooks triggered by changes in the graph

Hook name

File

Triggered by

Action

linking/rescan-trigger

rescan.lua

linkable SI added|removed or metadata-changed

schedules rescan-for-linking event

linking/linkable-removed

rescan.lua

linkable SI removed

destroys links related to the removed linkable

linking/follow

move-follow.lua

metadata-changed

schedules rescan-for-linking when the configured default sources/sinks are changed by the user

linking/move

move-follow.lua

metadata-changed

schedules rescan-for-linking when node target metadata properties are changed

linking/filter-forward-format

filter-forward-format.lua

filter stream SI added

configures filter nodes to have the same port format on both ends

linking/rescan-virtual-links

rescan-virtual-links.lua

link SI added, removed or metadata-changed

rescan-for-linking hooks, in order of execution

Hook name

File

Description

m-standard-event-source/rescan-done

module-standard-event-source.c

clears the rescan_scheduled flag

linking/rescan

rescan.lua

schedules select-target for each linkable session item

select-target hooks, in order of execution

Hook name

File

Description

linking/find-virtual-target

find-virtual-target.lua

linking/find-defined-target

find-defined-target.lua

Select the target that has been defined explicitly by the ‘target.object’ property or metadata

linking/find-filter-target

find-filter-target.lua

Select the target of a filter node, if the subject is a filter node

linking/find-default-target

find-default-target.lua

Select the default source/sink as target

linking/find-best-target

find-best-target.lua

Select target based on priority.session

linking/get-filter-from-target

get-filter-from-target.lua

Translate the found target to a filter target that should be linked instead

linking/prepare-link

prepare-link.lua

Break existing link if needed, check if the target is available for linking; send error to the client if needed

linking/link-target

link-target.lua

Create si-standard-link session item to create links between the subject linkable and the selected target