time off audio plugin host

The timeoffaudio::PluginHost class provides the primary interface for managing and interacting with audio plugins within a host application.

basic architecture

The architecture of the plugin host revolves around several key classes and functionalities:

• PluginHost: Manages the lifecycle and operations of audio plugins.
• PluginScan: Handles the scanning of available plugins and manages asynchronous loading.
• Plugin: Represents a single plugin instance with associated functionalities like window management and parameter control.

usage

Initialize the timeoffaudio::PluginHost as a member variable in your class:

class MyAudioProcessor {
public:
    MyAudioProcessor() : pluginHost(juce::File("path/to/plugin/list/file")) {
        // Initialization code here
    }

private:
    timeoffaudio::PluginHost pluginHost;
    // Other member variables
};

data model

The data model of the plugin host is built around the concept of plugins and their interactions. Key components include:

• PluginMap: Stores all active plugin instances. This map is an immutable data structure provided by the immer library, which allows for efficient and safe sharing of state across threads without needing locks. The map uses unique keys (KeyType which is typically a string) to identify each plugin instance.
• TransientPluginMap: Used for temporary changes to the plugin instances. It is a mutable version of PluginMap that allows changes to be made before being committed back to the immutable PluginMap.
• Plugin: Encapsulates an audio plugin instance along with its GUI window and connection information.

plugin discovery

Plugin discovery is managed by the PluginScan class, which supports asynchronous scanning of plugins across multiple threads. Key functions include:

• startScan: Initiates the scanning process for a specified plugin format.
• abortOngoingScan: Allows for the cancellation of any currently running scan.
• isScanInProgress: Returns a boolean indicating whether a scan is currently active.
• getScanStatus: Provides a snapshot of the current scan progress.

access patterns

The PluginHost class provides thread-safe access patterns for reading and writing plugin data. * A fundamental assumption made throughout the design is that the plugin map will only be modified by a single, non-realtime thread (typically the UI/message thread).*

• withWriteAccess: Used for operations that modify the plugin map from the non-realtime thread. It ensures changes are made within a controlled scope, safely committed back to the immutable PluginMap, then notifies listeners of the changes.

pluginHost.withWriteAccess([&] (PluginHost::TransientPluginMap& pluginMap) {
    // Modify pluginMap here
});

• withReadonlyAccess: Used for read-only operations on the plugin map from the non-realtime thread. It provides a consistent snapshot of the plugin state.

pluginHost.withReadonlyAccess([&] (const PluginHost::PluginMap& pluginMap) {
    // Read from pluginMap here
});

• withRealtimeAccess: Used for accessing the plugin map from the realtime thread. It ensures thread-safe and realtime-safe access to the latest plugin state (as read-only).

pluginHost.withRealtimeAccess([&] (const PluginHost::PluginMap& pluginMap) {
    // Access pluginMap in realtime context here
});

events / callbacks

The PluginHost::Listener interface provides callbacks for various events:

• scanProgressed: Updates on plugin scan progress.
• scanFinished: Called when a plugin scan completes.
• availablePluginsUpdated: Fired when the list of available plugins is updated.
• pluginInstanceLoadSuccessful: Occurs when a plugin instance is successfully loaded.
• pluginInstanceLoadFailed: Triggered if a plugin instance fails to load.
• pluginInstanceUpdated: Called when an existing plugin instance undergoes a significant change.
• pluginInstanceDeleted: Occurs when a plugin instance is removed.
• pluginInstanceParameterChanged: Fired when a parameter within a plugin instance changes.
• latenciesChanged: Called when the latency of one or more plugins changes.
• pluginWindowUpdated: Triggered when a plugin window is opened or closed.

plugin windows

The PluginWindow class manages the GUI for individual plugins. It provides options for customizing the appearance and behavior of plugin windows.

coming soon

Future updates may include built-in support for defining and playing arbitrary plugin graphs.