# LV2 Contexts Extension # # Allows for an LV2 plugin to have several independent contexts, each with its # own run callback and associated ports. # # Copyright (C) 2007 David Robillard # # Permission is hereby granted, free of charge, to any person obtaining a # copy of this software and associated documentation files (the "Software"), # to deal in the Software without restriction, including without limitation # the rights to use, copy, modify, merge, publish, distribute, sublicense, # and/or sell copies of the Software, and to permit persons to whom the # Software is furnished to do so, subject to the following conditions: # # The above copyright notice and this permission notice shall be included # in all copies or substantial portions of the Software. # # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL # THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR # OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, # ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR # OTHER DEALINGS IN THE SOFTWARE. @prefix ctx: . @prefix lv2: . @prefix rdf: . @prefix rdfs: . @prefix xsd: . @prefix doap: . @prefix foaf: . a lv2:Specification ; a lv2:Feature ; doap:name "LV2 Contexts" ; rdfs:comment """ An extension for LV2 plugins which have several execution contexts. Any host which supports this extension must pass an LV2_Feature to the plugin's instantiate method with URI http://lv2plug.in/ns/ext/contexts and a pointer to a 
struct {
	void* host_handle;
	void (*request_run)(void* host_handle, const char* context_uri);
}
where the plugin may call request_run with the given host_handle (from any context) to demand immediate execution of the context specified. If the host does not support blocking contexts, request_run may be set to NULL, but plugins which have a :BlockingContext which is :mandatory MUST NOT be instantiated. If the plugin has ANY context which is :hardRTCapable, request_run must be realtime safe (as defined by lv2:hardRTCapable). Unless otherwise stated, each context (defined by some URI) adds a new threading class similar to the Audio class defined by LV2. Each context has a run callback and a connect_port callback both in the same class (i.e. can't be called concurrently), but may be called concurrently with functions for other contexts (excluding the Instantiation class). Context properties such as ctx:hardRTCapable apply to both functions. The host MUST only call the correct connect_port function associated with the context for that port, i.e. it is an error to use the main LV2 connect_port function on a port with a context other than the main LV2 run function. """^^lv2:basicXHTML . ########################## ## Context Base Classes ## ########################## ctx:Context a rdfs:Class ; rdfs:label "LV2 Context" ; rdfs:comment """ A potentially concurrent context (callback) on a plugin. If a plugin supports a context (specified with the :optionalContext or ctx:requiredContext plugin properties) its extension_data function, called with the URI for that context, should return a context descriptor as defined by the specification of the context URI. If a plugin has any contexts, it MUST specify the associated context of ALL ports, with the :context port property.""" . ctx:RollingContext a rdfs:Class ; rdfs:subClassOf ctx:Context ; rdfs:comment """ A context which is is continually executed in blocks (like the standard LV2 run callback). Extension data is a pointer to a struct { void (*run)(LV2Handle instance, uint32_t sample_count); void (*connect_port)(LV2_Handle instance, uint32_t port, void* data); } When run is called, sample_count frames worth of input/output should be read from/written to all ports associated with this context. """ . ctx:BlockingContext a rdfs:Class ; rdfs:subClassOf ctx:Context ; rdfs:comment """ A context which is executed only when there is work to be done (e.g. a message is received). Extension data is a pointer to a struct LV2BlockingContext { bool (*run)(LV2Handle instance, uint8_t* valid_inputs, uint8_t* valid_outputs) void (*connect_port)(LV2_Handle instance, uint32_t port, void* data); } When run is called, any pending input in ports associated with this context should be read, and true returned iff output was written (meaning plugins connected to ports where output has been written should be executed). Before calling run, the host MUST set the nth bit of valid_inputs to 1 if the input port with index n has valid input that should be processed, otherwise 0. Before returning from run, the plugin MUST set the nth bit of valid_outputs to 1 if the port with index n was written to, otherwise 0. The header lv2_contexts.h provides utility functions for these purposes. The plugin MUST NOT touch any bits corresponding to ports on another context. """ . ####################### ## Plugin Properties ## ####################### ctx:optionalContext a rdf:Property ; rdfs:domain lv2:Plugin ; rdfs:range ctx:Context ; rdfs:label "Has an optional context" ; rdfs:comment """ Signifies a Plugin supports a certain context, defined by a URI, which may be ignored by the host.""" . ctx:requiredContext a rdf:Property ; rdfs:domain lv2:Plugin ; rdfs:range ctx:Context ; rdfs:label "Has a required context" ; rdfs:comment """ Signifies a Plugin supports a certain context, defined by a URI, which must be supported by the host for the plugin to function.""" . ##################### ## Port Properties ## ##################### ctx:context a rdf:Property ; rdfs:domain lv2:Port ; rdfs:range ctx:Context ; rdfs:label "Is used by context" ; rdfs:comment """ The context a particular port is associated with; the port will only be connected/read/written by that context. If no context is specified, the port is considered part of the default LV2 audio context.""" . ################################## ## Specific context definitions ## ################################## ctx:AudioContext a rdfs:Class ; rdfs:subClassOf ctx:Context ; rdfs:comment """ The context of the core LV2 run method (LV2_Descriptor::run). """ . ctx:StatelessAudioContext a rdfs:Class ; rdfs:subClassOf ctx:Context ; rdfs:comment """ The usual LV2 run context (ctx:AudioContext), with the additional property that the plugin has no internal state whatsoever (other than the sample rate and the locations ports are currently connected to). On a plugin with a ctx:StatelessAudioContext, the nframes parameter to run is meaningless and ignored by the plugin, and the host may assume that any call to run with a given set of inputs will produce the exact same set of outputs (i.e. the plugin's run method is purely functional). This context inherently conflicts with lv2:isLive, a plugin MUST NOT have both a ctx:StatelessAudioContext and the lv2:isLive feature. For easy compatibility with hosts that don't care whether the audio context is stateless or not, this context should be listed as a ctx:optionalContext (since the default LV2 context is implicitly present). """ . ctx:MessageContext a rdfs:Class ; rdfs:subClassOf ctx:BlockingContext ; rdfs:comment """ A blocking context for on-demand message-like processing. The plugin's lv2:hardRTCapable property does not apply to the message context, there are no realtime restrictions on the plugin's message context, and no syncronisation guarantees between the message context and any other context. """ .