|Prefixes||lv2 owl rdf rdfs ui xsd|
This extension defines an interface that can be used in LV2 plugins and hosts to create UIs for plugins. The UIs are similar to plugins and reside in shared object files in an LV2 bundle. UIs are associated with a plugin in RDF using the triples:
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 probably a good idea to keep them separate so that hosts that don't want UIs don't have to load the UI code. A UI MUST specify its class in the RDF data (ui:GtkUI in the above example). The class defines what type the UI is, e.g. 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 way people other than the plugin author can write plugin UIs independently without editing the original plugin bundle.
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 occcurs via ports.
A UI where the LV2_Widget is a pointer to a NSView, the basic view type for the Cocoa API (formerly OpenStep). This is the native UI type on Mac OS X.
A UI where the LV2_Widget is a pointer to a Gtk+ 3.0 compatible GtkWidget, and the host guarantees that the Gtk+ library has been initialised and the Glib main loop is running before a UI of this type is instantiated.
A UI where the LV2_Widget is a pointer to a Gtk+ 2.0 compatible GtkWidget, and the host guarantees that the Gtk+ library has been initialised and the Glib main loop is running before a UI of this type is instantiated.
A port notification. This describes which ports the host must send notifications to the UI about. The port can be specific by index, using the ui:portIndex property, or symbol, using the lv2:symbol property. Since port indices are not guaranteed to be stable between different revisions (or even instantiations) of a plugin, symbol is recommended, and index may only be used by UIs shipped in the same bundle as the plugin.
|Restriction on ui:plugin|
|In domain of||ui:protocol|
|In range of||ui:portNotification|
A PortProtocol defines a method to communicate port data between a UI and plugin.
Any 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.|
Any 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().|
Any 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().|
|In range of||ui:protocol|
A UI where the LV2_Widget is a pointer to a Qt4 compatible QWidget, and the host guarantees that the Qt4 library has been initialised and the Qt4 main loop is running before a UI of this type is instantiated.
A UI where the LV2_Widget is a Windows HWND window ID. Note this is actually an unsigned 32-bit integer, i.e. the LV2_Widget is not a pointer to a HWND but should be interpreted as an HWND itself. This is the native UI type on Microsoft Windows.
A UI where the LV2_Widget is an X11 window ID. Note this is actually an integer, i.e. the LV2_Widget is not a pointer to an X11 window ID, but should be itself taken as an integer value. This is the native UI type on most POSIX systems.
Indicates a particular type that the UI should be notified of. In the case of ports where several types of data can be present (e.g. event ports), this can be used to indicate that only a particular type of data should cause notification. This is useful where port traffic is very dense, but only a certain small number of events are actually of interest to the UI.
|OWL Type||Object Property|
If a UI requires this feature it indicates the same thing as ui:noUserResize, and additionally it means that the UI will not resize the main widget on its own - it will always remain the same size (e.g. a pixmap based GUI). This feature may not make sense for all UI types. The data pointer for the LV2_Feature for this feature should always be set to NULL.
A protocol for transferring single floating point values. The rules for this protocol are:
|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 |
|Write Format||A single |
|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.|
The parent for the UI.
This feature can be used to pass a parent (e.g. a widget, container, canvas, etc.) 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 LV2_Widget the UI would return (e.g. for a GtkUI the data would be a pointer to a GtkWidget which is a GtkContainer). This is particularly useful for cross-toolkit 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 absolutely necessary for them to work at all.
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, e.g. 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:
|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.|
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.
A feature that allows the UI to notify the host about its current size, or request a size change. 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.
A feature to notify the host that the user has grabbed a particular 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 morotised 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.