# LV2 Options

http://lv2plug.in/ns/ext/options
Instantiation time options.

Version | 1.2
Date | 2018-03-16
Discuss | devel@lists.lv2plug.in (subscribe)
Developer | David Robillard

- Index
- Reference
- History
- API

This extension defines a facility for options, which are dynamic properties that may be changed at run time.

There are two facilities for passing options to an instance: opts:options allows passing options at instantiation time, and the opts:interface interface allows options to be dynamically set and retrieved after instantiation.

Note that this extension is only for allowing hosts to configure plugins, and is not a live control mechanism. For real-time control, use event-based control via an atom:AtomPort with an atom:Sequence buffer.

Instances may indicate they require an option with the opts:requiredOption property, or that they optionally support an option with the opts:supportedOption property.

## Index

Classes | Properties | Instances | Files
--- | --- | --- | ---
Option | requiredOption supportedOption | interface options | lv2-options.doap.ttl options.h options.ttl

## Reference

### Class opts:Option

Option

A property intended to be used as a static option for an instance.

It is not required for a property to explicitly be an Option in order to be used as such. However, properties which are primarily intended for use as options, or are at least particularly useful as options, should be explicitly given this type for documentation purposes, and to assist hosts in discovering option definitions.

Sub-class of | rdf:Property
In range of | opts:requiredOption
| opts:supportedOption

### Property opts:requiredOption

required option

An option required by the instance to function at all. The host MUST pass a value for the specified option via opts:options in order to create an instance.

Note that use of this property may reduce the number of compatible hosts. Wherever possible, it is better to list options with opts:supportedOption and fall back to a reasonable default value if it is not provided.

OWL Type | Object Property
Range | opts:Option

### Property opts:supportedOption

supported option

An option supported or understood by the instance. The host SHOULD provide a value for the specified option if one is known, or provide the user an opportunity to specify one if one is Indicates that the instance host MUST pass a value for the specified option in order to instantiate the instance.

OWL Type | Object Property
Range | opts:Option

### Instance opts:interface

An interface (LV2_Options_Interface) for dynamically setting and getting options. Note this is intended for use by the host for configuring plugins only, and and is not a live plugin control mechanism.

The plugin data file should describe this like so:

    @prefix opts: <http://lv2plug.in/ns/ext/options#> .

    <plugin>
        a lv2:Plugin ;
        lv2:extensionData opts:interface .

Type | lv2:ExtensionData

### Instance opts:options

options

The feature used to provide options to an instance.

To implement this feature, hosts MUST pass an LV2_Feature to the appropriate instantiate method with this URI and data pointed to an array of LV2_Options_Option terminated by an element with both key and value set to zero. The instance should cast this data pointer to `const LV2_Options_Option*` and scan the array for any options of interest. The instance MUST NOT modify the options array in any way.

Note that requiring this feature may reduce the number of compatible hosts. Unless some options are strictly required by the instance, this feature SHOULD be listed as a lv2:optionalFeature.

Type | lv2:Feature

## History

Version 1.2 (2013-01-10)
  - Set the range of opts:requiredOption and opts:supportedOption to opts:Option.
Version 1.0 (2012-10-14)
  - Initial release.