ui
type: Project
license: isc
name: LV2 UI
shortdesc: User interfaces for LV2 plugins.
created: 2006-00-00
developer: larsl
maintainer: me
documentation: This extension makes it possible to create user interfaces for LV2 plugins. UIs are implemented as an LV2UI_Descriptor loaded via lv2ui_descriptor() in a shared library, and are distributed in bundles just like plugins. UIs are associated with plugins in data: :::turtle @prefix ui: <http://lv2plug.in/ns/extensions/ui#> . <http://my.plugin> ui:ui <http://my.pluginui> . <http://my.pluginui> a ui:X11UI ; lv2:binary <myui.so> . where `http://my.plugin` is the URI of the plugin, `http://my.pluginui` is the URI of the plugin UI and `myui.so` is the relative URI to the shared object file. While it is possible to have the plugin UI and the plugin in the same shared object file, it is a good idea to keep them separate so that hosts can avoid loading the UI code if they do not need it. A UI MUST specify its class in the RDF data (`ui:X11UI` in the above example). The class defines what type the UI is, for example what graphics toolkit it uses. Any type of UI class can be defined separately from this extension. It is possible to have multiple UIs for the same plugin, or to have the UI for a plugin in a different bundle from the actual plugin. This allows plugin UIs to be written independently. Note that the process that loads the shared object file containing the UI code and the process that loads the shared object file containing the actual plugin implementation are not necessarily the same process (and not even necessarily on the same machine). This means that plugin and UI code MUST NOT use singletons and global variables and expect them to refer to the same objects in the UI and the actual plugin. The function callback interface defined in this header is the only method of communication between UIs and plugin instances (extensions may define more, though this is discouraged unless absolutely necessary since the significant benefits of network transparency and serialisability are lost). UI functionality may be extended via features, much like plugins: :::turtle <http://my.p…

GtkUI
documentation: The host must guarantee that the Gtk+ 2 library has been initialised and the Glib main loop is running before the UI is instantiated. Note that this UI type is not suitable for binary distribution since multiple versions of Gtk can not be used in the same process.

Gtk3UI
documentation: The host must guarantee that the Gtk+ 3 library has been initialised and the Glib main loop is running before the UI is instantiated. Note that this UI type is not suitable for binary distribution since multiple versions of Gtk can not be used in the same process.

Gtk4UI
documentation: The host must guarantee that the Gtk+ 4 library has been initialised and the Glib main loop is running before the UI is instantiated. Note that this UI type is not suitable for binary distribution since multiple versions of Gtk can not be used in the same process.

Qt4UI
documentation: The host must guarantee that the Qt4 library has been initialised and the Qt4 main loop is running before the UI is instantiated. Note that this UI type is not suitable for binary distribution since multiple versions of Qt can not be used in the same process.

Qt5UI
documentation: The host must guarantee that the Qt5 library has been initialised and the Qt5 main loop is running before the UI is instantiated. Note that this UI type is not suitable for binary distribution since multiple versions of Qt can not be used in the same process.

Qt6UI
documentation: The host must guarantee that the Qt6 library has been initialised and the Qt6 main loop is running before the UI is instantiated. Note that this UI type is not suitable for binary distribution since multiple versions of Qt can not be used in the same process.

X11UI
documentation: Note that the LV2UI_Widget for this type of UI is not a pointer, but should be interpreted directly as an X11 `Window` ID. This is the native UI type on most POSIX systems.

WindowsUI
documentation: Note that the LV2UI_Widget for this type of UI is not a pointer, but should be interpreted directly as a `HWND`. This is the native UI type on Microsoft Windows.

CocoaUI
documentation: This is the native UI type on Mac OS X.

binary
documentation: This property is redundant and deprecated: new UIs should use lv2:binary instead, however hosts must still support ui:binary.

makeSONameResident
documentation: This feature was intended to support UIs that link against toolkit libraries which may not be unloaded during the lifetime of the host. This is better achieved by using the appropriate flags when linking the UI, for example `gcc -Wl,-z,nodelete`.

noUserResize
documentation: If a UI has this feature, it indicates that it does not make sense to let the user resize the main widget, and the host should prevent that. This feature may not make sense for all UI types. The data pointer for this feature should always be set to NULL.

fixedSize
documentation: If a UI has this feature, it indicates the same thing as ui:noUserResize, and additionally that the UI will not resize itself on its own. That is, the UI will always remain the same size. This feature may not make sense for all UI types. The data pointer for this feature should always be set to NULL.

scaleFactor
documentation: HiDPI (High Dots Per Inch) displays have a high resolution on a relatively small form factor. Many systems use a scale factor to compensate for this, so for example, a scale factor of 2 means things are drawn twice as large as normal. Hosts can pass this as an option to UIs to communicate this information, so that the UI can draw at an appropriate scale.

backgroundColor
documentation: The background color of the host's UI. The host can pass this as an option so that UIs can integrate nicely with the host window around it. Hosts should pass this as an option to UIs with an integer RGBA32 color value. If the value is a 32-bit integer, it is guaranteed to be in RGBA32 format, but the UI must check the value type and not assume this, to allow for other types of color in the future.

foregroundColor
documentation: The foreground color of the host's UI. The host can pass this as an option so that UIs can integrate nicely with the host window around it. Hosts should pass this as an option to UIs with an integer RGBA32 color value. If the value is a 32-bit integer, it is guaranteed to be in RGBA32 format, but the UI must check the value type and not assume this, to allow for other types of color in the future.

parent
documentation: This feature can be used to pass a parent that the UI should be a child of. The format of data pointer of this feature is determined by the UI type, and is generally the same type as the LV2UI_Widget that the UI would return. For example, for a ui:X11UI, the parent should be a `Window`. This is particularly useful for embedding, where the parent often must be known at construction time for embedding to work correctly. UIs should not _require_ this feature unless it is necessary for them to work at all, but hosts should provide it whenever possible.

PortNotification
documentation: This describes which ports the host must send notifications to the UI about. The port must be specific either by index, using the ui:portIndex property, or symbol, using the lv2:symbol property. Since port indices are not guaranteed to be stable, using the symbol is recommended, and the inde MUST NOT be used except by UIs that are shipped in the same bundle as the corresponding plugin.

portNotification
documentation: Specifies that a UI should receive notifications about changes to a particular port's value via LV2UI_Descriptor::port_event(). For example: :::turtle eg:ui a ui:X11UI ; ui:portNotification [ ui:plugin eg:plugin ; lv2:symbol "gain" ; ui:protocol ui:floatProtocol ] .

notifyType
documentation: Specifies a particular type that the UI should be notified of. This is useful for message-based ports where several types of data can be present, but only some are interesting to the UI. For example, if UI control is multiplexed in the same port as MIDI, this property can be used to ensure that only the relevant events are forwarded to the UI, and not potentially high frequency MIDI data.

resize
documentation: This feature corresponds to the LV2UI_Resize struct, which should be passed with the URI LV2_UI__resize. This struct may also be provided by the UI as extension data using the same URI, in which case it is used by the host to request that the UI change its size.

portMap
documentation: This makes it possible to implement and distribute UIs separately from the plugin binaries they control. This feature corresponds to the LV2UI_Port_Index struct, which should be passed with the URI LV2_UI__portIndex.

portSubscribe
documentation: This makes it possible for a UI to explicitly request a particular style of update from a port at run-time, in a more flexible and powerful way than listing subscriptions statically allows. This feature corresponds to the LV2UI_Port_Subscribe struct, which should be passed with the URI LV2_UI__portSubscribe.

touch
documentation: This is useful for automation, so the host can allow the user to take control of a port, even if that port would otherwise be automated (much like grabbing a physical motorised fader). It can also be used for MIDI learn or in any other situation where the host needs to do something with a particular control and it would be convenient for the user to select it directly from the plugin UI. This feature corresponds to the LV2UI_Touch struct, which should be passed with the URI LV2_UI__touch.

requestValue
documentation: This allows a plugin UI to request a new parameter value using the host's UI, for example by showing a dialog or integrating with the host's built-in content browser. This should only be used for complex parameter types where the plugin UI is not capable of showing the expected native platform or host interface to choose a value, such as file path parameters. This feature corresponds to the LV2UI_Request_Value struct, which should be passed with the URI LV2_UI__requestValue.

idleInterface
documentation: To support this feature, the UI should list it as a lv2:optionalFeature or lv2:requiredFeature in its data, and also as lv2:extensionData. When the UI's extension_data() is called with this URI (LV2_UI__idleInterface), it should return a pointer to an LV2UI_Idle_Interface. To indicate support, the host should pass a feature to instantiate() with this URI, with NULL for data.

showInterface
documentation: This allows UIs to gracefully degrade to separate windows when the host is unable to embed the UI widget for whatever reason. When the UI's extension_data() is called with this URI (LV2_UI__showInterface), it should return a pointer to an LV2UI_Show_Interface.

PortProtocol
documentation: A PortProtocol MUST define: Port Type : Which plugin port types the buffer type is valid for. Feature Data : What data (if any) should be passed in the LV2_Feature. A PortProtocol for an output port MUST define: Update Frequency : When the host should call port_event(). Update Format : The format of the data in the buffer passed to port_event(). Options : The format of the options passed to subscribe() and unsubscribe(). A PortProtocol for an input port MUST define: Write Format : The format of the data in the buffer passed to write_port(). Write Effect : What happens when the UI calls write_port(). For an example, see ui:floatProtocol or ui:peakProtocol. PortProtocol is a subclass of lv2:Feature, so UIs use lv2:optionalFeature and lv2:requiredFeature to specify which PortProtocols they want to use.

floatProtocol
documentation: A protocol for transferring single floating point values. The rules for this protocol are: Port Type : lv2:ControlPort Feature Data : None. Update Frequency : The host SHOULD call port_event() as soon as possible when the port value has changed, but there are no timing guarantees. Update Format : A single float. Options : None. Write Format : A single float. Write Effect : The host SHOULD set the port to the received value as soon as possible, but there is no guarantee that run() actually sees this value.

peakProtocol
documentation: This port protocol defines a way for the host to send continuous peak measurements of the audio signal at a certain port to the UI. The intended use is visualisation, for example an animated meter widget that shows the level of the audio input or output. A contiguous sequence of audio samples for which a peak value has been computed is called a _measurement period_. The rules for this protocol are: Port Type : lv2:AudioPort Feature Data : None. Update Frequency : The host SHOULD call port_event() at regular intervals. The measurement periods used for calls to port_event() for the same port SHOULD be contiguous (i.e. the measurement period for one call should begin right after the end of the measurement period for the previous call ends) unless the UI has removed and re-added the port subscription between those calls. However, UIs MUST NOT depend on either the regularity of the calls or the contiguity of the measurement periods; hosts may change the call rate or skip calls for performance or other reasons. Measurement periods for different calls to port_event() for the same port MUST NOT overlap. Update Format : A single LV2UI_Peak_Data object. Options : None. Write Format : None. Write Effect : None.