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Automation Internals

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M374LX edited this page Jan 11, 2022 · 3 revisions

Automation Internals

This page tries to explain how the LMMS code handles automation patterns and controllers.

Basic definitions

  • Models are the base classes for all data represented by widgets like knobs, sliders, spinboxes...

  • Models that can be connected to AutomationClips or Controllers are AutomatableModels

  • AutomationClip contains a list of all AutomatableModel's connected (internally named m_objects). AutomationClip is a TrackContentObject (TCO).

  • AutomationTracks contain data for one automation track, represented as AutomationTrackView in the UI. This is basically a whole automation track row in the Song Editor.

  • An AutomationTrack can contain multiple AutomationClips, represented as AutomationClipViews in the UI.

Automation through Controllers

Controller automation is simple: The Models of the widgets have the controller linked via pointers. A call to AutomatableModel::value() returns

  • the Controller's value (recalculated to fit the Model using controllerValue), or else
  • the non-automated m_value

Automation through Automation Clips

Automation through patterns requires pre-calculation by the Song class, as these patterns can be recorded, or require interpolation.

  • When an AutomationTrackView::dropEvent occurs,
    1. the ID of the AutomatableModel is provided in the drop event
    2. the AutomationTrackView looks up that ID in the Engin::projectJournal to get the AutomatableModel
    3. the AutomationTrack creates a new AutomationClip
    4. the AutomatableModel gets added to the new AutomationClip
    5. the connection is now done
  • When a Song is played, Song::processNextBuffer calls Song::processAutomations, which
    1. calls automatedValuesAt, i.e. returns all AutomatableModels at the current position in a QMap<AutomatableModel*, float> by using the AutomationClip members objects() and valueAt()
    2. calls all AutomatableModel::setAutomatedValue with the pair of the QMap, i.e. assigns floats to the AutomatableModels' static m_values

Automation and savefiles

Automation is usually done by saving an XML node "automationpattern" (inside a node "automationtrack") which saves all connected models as "object" nodes. Each such node specifies an "id" attribute. AutomatableModel also have such an "id" attribute, so they can be matched in the journalling system. The AutomatableModel usually is stored as a node having its name, or as a node "quoted-model" with an attribute "quoted-name".

When loading a savefile, LMMS can load automation patterns and automatable models in arbitrary order. When loading a pattern's object node, a variable AutomationClip::m_idsToResolve gets filled with the journalling IDs. After the full song has been loaded, AutomationClip::resolveAllIDs() adds model pointers to the AutomationClip::m_objects array.

Now, when AutomationClipView::paintEvent is being called to draw a pattern view, the minimum and maximum value are fetched directly from the first object (i.e. the first AutomatableModel) of the AutomationClip.

See also https://docs.lmms.io/developer-guides/core/controlling-playback

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