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:
@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 (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:
<http://my.pluginui> lv2:requiredFeature <http://my.feature> .
<http://my.pluginui> lv2:optionalFeature <http://my.feature> .
The rules for a UI with a required or optional feature are identical to those of lv2:Plugin instances: if a UI declares a feature as required, the host is NOT allowed to load it unless it supports that feature; and if it does support a feature, it MUST pass an appropriate LV2_Feature struct to the UI's instantiate() method. This extension defines several standard features for common functionality.
UIs written to this specification do not need to be thread-safe. All functions
may only be called in the UI thread
. There is only one UI thread (for
toolkits, the one the UI main loop runs in). There is no requirement that a
UI
actually be a graphical widget.
Note that UIs are completely separate from plugins. From the plugin's perspective, control from a UI is indistinguishable from any other control, as it all occurs via ports.
Index
Classes
Gtk3UI
Class| Label | GTK3 UI |
|---|---|
| Subclass of | UI |
A UI where the widget is a pointer to a Gtk+ 3.0 GtkWidget.
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.
GtkUI
Class| Label | GTK2 UI |
|---|---|
| Subclass of | UI |
A UI where the widget is a pointer to a Gtk+ 2.0 GtkWidget.
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.
PortNotification
Class| Label | Port Notification |
|---|---|
| In domain of | notifyType |
| plugin | |
| portIndex | |
| protocol | |
| In range of | portNotification |
A description of port updates that a host must send a UI.
This describes which ports the host must send notifications to the UI about. The port must be specific either by index, using the 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.
- Restriction on plugin
- owl:cardinality 1
A PortNotification MUST have exactly one ui:plugin.
PortProtocol
Class| Label | Port Protocol |
|---|---|
| Subclass of | lv2:Feature |
| In range of | protocol |
A method to communicate port data between a UI and plugin.
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 floatProtocol or peakProtocol.
PortProtocol is a subclass of lv2:Feature, so UIs use lv2:optionalFeature and lv2:requiredFeature to specify which PortProtocols they want to use.
Qt4UI
Class| Label | Qt4 UI |
|---|---|
| Subclass of | UI |
A UI where the widget is a pointer to a Qt4 QWidget.
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
Class| Label | Qt5 UI |
|---|---|
| Subclass of | UI |
A UI where the widget is a pointer to a Qt5 QWidget.
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.
UI
ClassWindowsUI
Class| Label | Windows UI |
|---|---|
| Subclass of | UI |
A UI where the widget is a Windows HWND window ID.
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.
X11UI
Class| Label | X11 UI |
|---|---|
| Subclass of | UI |
A UI where the widget is an X11 Window window ID.
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.
Properties
backgroundColor
Property| Label | background color |
|---|---|
| Type | Datatype Property |
The background color of the host's UI.
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.
binary
Property| Label | binary |
|---|---|
| Type | Object Property |
| owl:deprecated | true |
| owl:sameAs | lv2:binary |
The shared library that a UI resides in.
This property is redundant and deprecated: new UIs should use lv2:binary instead, however hosts must still support binary.
foregroundColor
Property| Label | foreground color |
|---|---|
| Type | Datatype Property |
The foreground color of the host's UI.
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.
notifyType
Property| Label | notify type |
|---|---|
| Domain | PortNotification |
| Type | Object Property |
A particular type that the UI should be notified of.
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.
plugin
Property| Label | plugin |
|---|---|
| Domain | PortNotification |
| Range | lv2:Plugin |
| Type | Object Property |
The plugin a portNotification applies to.
portIndex
Property| Label | port index |
|---|---|
| Domain | PortNotification |
| Range | xsd:decimal |
| Type | Datatype Property |
The index of the port a portNotification applies to.
portNotification
Property| Label | port notification |
|---|---|
| Domain | UI |
| Range | PortNotification |
| Type | Object Property |
Specifies a port notification that is required by a UI.
Specifies that a UI should receive notifications about changes to a particular port's value via LV2UI_Descriptor::port_event().
For example:
eg:ui
a ui:X11UI ;
ui:portNotification [
ui:plugin eg:plugin ;
lv2:symbol "gain" ;
ui:protocol ui:floatProtocol
] .
protocol
Property| Label | protocol |
|---|---|
| Domain | PortNotification |
| Range | PortProtocol |
| Type | Object Property |
The protocol to be used for this notification.
scaleFactor
Property| Label | scale factor |
|---|---|
| Range | xsd:float |
| Type | Datatype Property |
Scale factor for high resolution screens.
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.
ui
Property| Label | user interface |
|---|---|
| Domain | lv2:Plugin |
| Range | UI |
| Type | Object Property |
Relates a plugin to a UI that applies to it.
updateRate
Property| Label | update rate |
|---|---|
| Range | xsd:float |
| Type | Datatype Property |
The target rate, in Hz, to send updates to the UI.
windowTitle
Property| Label | window title |
|---|---|
| Range | xsd:string |
| Type | Datatype Property |
The title for the window shown by LV2UI_Show_Interface.
Instances
fixedSize
Instance| Label | fixed size |
|---|---|
| Type | lv2:Feature |
Non-resizable UI that will never resize itself.
If a UI has this feature, it indicates the same thing as 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.
floatProtocol
Instance| Label | float protocol |
|---|---|
| Type | PortProtocol |
A protocol for transferring single floating point values.
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.
idleInterface
Instance| Label | idle interface |
|---|---|
| Type | lv2:ExtensionData |
| lv2:Feature |
A feature that provides a callback for the host to drive the UI.
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.
makeSONameResident
Instance| Label | make SO name resident |
|---|---|
| Type | lv2:Feature |
| owl:deprecated | true |
UI binary must not be unloaded.
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
Instance| Label | no user resize |
|---|---|
| Type | lv2:Feature |
Non-resizable UI.
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.
parent
Instance| Label | parent |
|---|---|
| Type | lv2:Feature |
The parent for a UI.
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 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.
peakProtocol
Instance| Label | peak protocol |
|---|---|
| Type | PortProtocol |
A protocol for sending continuous peak measurements of an audio signal.
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.
portMap
Instance| Label | port map |
|---|---|
| Type | lv2:Feature |
A feature for accessing the index of a port by symbol.
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
Instance| Label | port subscribe |
|---|---|
| Type | lv2:Feature |
A feature for dynamically subscribing to updates from a port.
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.
requestValue
Instance| Label | request value |
|---|---|
| Type | lv2:Feature |
A feature to request a parameter value from the user via the host.
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.
resize
Instance| Label | resize |
|---|---|
| Type | lv2:ExtensionData |
| lv2:Feature | |
| owl:deprecated | true |
A feature that provides control of, and notifications about, a UI's size.
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.
showInterface
Instance| Label | show interface |
|---|---|
| Type | lv2:ExtensionData |
An interface for showing and hiding a window for a UI.
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.
touch
Instance| Label | touch |
|---|---|
| Type | lv2:Feature |
A feature to notify that the user has grabbed a port control.
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.
A UI where the widget is a pointer to a NSView.
This is the native UI type on Mac OS X.