psyn/lv2_event.h

/* lv2_event.h - C header file for the LV2 events extension.
 * 
 * Copyright (C) 2006-2007 Lars Luthman <lars.luthman@gmail.com>
 * Copyright (C) 2008 Dave Robillard <dave@drobilla.net>
 * 
 * This header is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This header is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this header; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place, Suite 330, Boston, MA 01222-1307 USA
 */

#ifndef LV2_EVENT_H
#define LV2_EVENT_H
 
#define LV2_EVENT_URI "http://lv2plug.in/ns/ext/event"
#define LV2_EVENT_AUDIO_STAMP 0

#include <stdint.h>

/** @file
 * This header defines the code portion of the LV2 events extension with
 * URI <http://lv2plug.in/ns/ext/event>.
 *
 * Below, the URI prefix 'lv2ev' is assumed to expand to 
 * <http://lv2plug.in/ns/ext/event#>.
 *
 * This extension is a generic transport mechanism for time stamped events
 * of any type (e.g. MIDI, OSC, ramps, etc).  Each port can transport mixed
 * events of any type; the type of events and timestamps are defined by a URI
 * which is mapped to an integer by the host for performance reasons.
 *
 * This extension requires the host to support the LV2 URI Map extension.
 * This requirement is implicit - a plugin does not have to list the URI Map
 * feature as required or optional in its RDF data for the host to provide
 * the URI Map LV2_Feature in the instantiation function.
 *
 * Any host which supports this extension MUST guarantee that any call to
 * the LV2 URI Map uri_to_id function with the URI of this extension as the
 * 'map' argument returns a value within the range of uint16_t.
 */


/** The best Pulses Per Quarter Note for tempo-based uint32_t timestmaps.
 * Equal to 2^12 * 5 * 7 * 9 * 11 * 13 * 17, which is evenly divisble
 * by all integers from 1 through 18 inclusive, and powers of 2 up to 2^12.
 */
static const uint32_t LV2_EVENT_PPQN = 3136573440U;


/** An LV2 event (header only).
 *
 * LV2 events are generic time-stamped containers for any type of event.
 * The type field defines the format of a given event's contents.
 *
 * This struct defines the header of an LV2 event.  An LV2 event, as specified
 * in this extension, is a single chunk of POD (plain old data), usually 
 * contained in a flat buffer (see LV2_EventBuffer below), that can be safely
 * copied using a simple:
 *
 * memcpy(ev_copy, ev, sizeof(LV2_Event) + ev->size);  (or equivalent)
 *
 * However, events with event type 0 need to be handled specially (see below).
 */
typedef struct {

	/** The frames portion of timestamp.  The units used here can optionally
	 * be set for a port (with lv2ev:supportsTimeStamp and related 
	 * properties), otherwise this is audio frames, corresponding to the 
	 * sample_count parameter of the LV2 run method (e.g. frame 0 is the 
	 * first frame for that call to run).
	 */
	uint32_t frames;

	/** The sub-frames portion of timestamp.  The units used here can
	 * optionally be set for a port (with lv2ev:supportsTimeStamp and 
	 * related properties), otherwise this is 1/(2^32) of an audio frame.
	 */
	uint32_t subframes;
	
	/** The type of this event, as a number which represents some URI
	 * defining an event type.  This value MUST be some value previously
	 * returned from a call to the uri_to_id function defined in the LV2
	 * URI map extension (see lv2_uri_map.h).
	 *
	 * There are special rules which must be followed depending on the type
	 * of an event.  If the plugin recognizes an event type, the definition
	 * of that event type will describe how to interpret the event, and
	 * any required behaviour.  Otherwise, if the type is 0, this event is a
	 * non-POD event and lv2_event_unref MUST be called if the event is
	 * 'dropped' (see below).  Even if the plugin does not understand an 
	 * event, it may pass the event through to an output by simply copying 
	 * (and NOT calling lv2_event_unref).  These rules are designed to 
	 * allow for generic event handling plugins and large non-POD events, 
	 * but with minimal hassle on simple plugins that "don't care" about 
	 * these more advanced features.
	 *
	 * Plugins should not interpret type 0 events in any way unless
	 * specified by another extension.
	 */
	uint16_t type;

	/** The size of the data portion of this event in bytes, which 
	 * immediately follows.  The header size (12 bytes) is not included in 
	 * this value.
	 */
	uint16_t size;

	/* size bytes of data follow here */

} LV2_Event;



/** A buffer of LV2 events (header only).
 *
 * This struct is used as the port buffer for LV2 plugin ports that have the
 * port class lv2ev:EventPort.
 * 
 * The data member points to a buffer that contains an event header (defined 
 * by struct* LV2_Event), followed by that event's contents (padded to 64 bits),
 * followed by another header, etc:
 *
 * |       |       |       |       |       |       |
 * | | | | | | | | | | | | | | | | | | | | | | | | |
 * |FRAMES |SUBFRMS|TYP|LEN|DATA..DATA..PAD|FRAMES | ...
 */
typedef struct {
	
	/** The contents of the event buffer.  This may or may not reside in the
	 * same block of memory as this header, plugins must not assume either.
	 * The host guarantees this points to at least capacity bytes of 
         * allocated memory (though only size bytes of that are valid events).
	 */
	uint8_t* data;

	/** The size of this event header in bytes (including everything).
	 *
	 * This is to allow for extending this header in the future without
	 * breaking binary compatibility.  Whenever this header is copied,
	 * it MUST be done using this field (and NOT the sizeof this struct).
	 */
	uint16_t header_size;

	/** The type of the time stamps for events in this buffer.
	 * As a special exception, '0' always means audio frames and subframes
	 * (1/UINT32_MAX'th of a frame) in the sample rate passed to instantiate.
	 * INPUTS: The host must set this field to the numeric ID of some URI
	 *     defining the meaning of the frames/subframes fields of contained
	 *     events (obtained by the LV2 URI Map uri_to_id function with the URI
	 *     of this extension as the 'map' argument, see lv2_uri_map.h).
	 *     The host must never pass a plugin a buffer which uses a stamp type
	 *     the plugin does not 'understand'.  The value of this field must
	 *     never change, except when connect_port is called on the input
	 *     port, at which time the host MUST have set the stamp_type field to
	 *     the value that will be used for all subsequent run calls.
	 * OUTPUTS: The plugin may set this to any value that has been returned
	 *     from uri_to_id with the URI of this extension for a 'map' argument.
	 *     When connected to a buffer with connect_port, output ports MUST set
	 *     this field to the type of time stamp they will be writing.  On any
	 *     call to connect_port on an event input port, the plugin may change
	 *     this field on any output port, it is the responsibility of the host
	 *     to check if any of these values have changed and act accordingly.
	 */
	uint16_t stamp_type;

	/** The number of events in this buffer.
	 * INPUTS: The host must set this field to the number of events
	 *     contained in the data buffer before calling run().
	 *     The plugin must not change this field.
	 * OUTPUTS: The plugin must set this field to the number of events it
	 *     has written to the buffer before returning from run().
	 *     Any initial value should be ignored by the plugin.
	 */
	uint32_t event_count;

	/** The size of the data buffer in bytes.
	 * This is set by the host and must not be changed by the plugin.
	 * The host is allowed to change this between run() calls.
	 */
	uint32_t capacity;

	/** The size of the initial portion of the data buffer containing data.
	 * INPUTS: The host must set this field to the number of bytes used
	 *     by all events it has written to the buffer (including headers)
	 *     before calling the plugin's run().
	 *     The plugin must not change this field.
	 * OUTPUTS: The plugin must set this field to the number of bytes
	 *     used by all events it has written to the buffer (including headers)
	 *     before returning from run().
	 *     Any initial value should be ignored by the plugin.
	 */
	uint32_t size;

} LV2_Event_Buffer;


/** Opaque pointer to host data. */
typedef void* LV2_Event_Callback_Data;


/** The data field of the LV2_Feature for this extension.
 *
 * To support this extension the host must pass an LV2_Feature struct to the
 * plugin's instantiate method with URI "http://lv2plug.in/ns/ext/event"
 * and data pointed to an instance of this struct.  The plugin does not have
 * to list that URI as a required or optional feature in its RDF data - the 
 * host MUST pass this LV2_Feature if the plugin has an port of class 
 * lv2ev:EventPortthat the host connects to.
 */
typedef struct {
	
	/** Opaque pointer to host data.
	 *
	 * The plugin MUST pass this to any call to functions in this struct.
	 * Otherwise, it must not be interpreted in any way.
	 */
	LV2_Event_Callback_Data callback_data;
	
	/** Take a reference to a non-POD event.
	 *
	 * If a plugin receives an event with type 0, it means the event is a
	 * pointer to some object in memory and not a flat sequence of bytes
	 * in the buffer.  When receiving a non-POD event, the plugin already
	 * has an implicit reference to the event.  If the event is stored AND
	 * passed to an output, or passed to two outputs, lv2_event_ref MUST 
	 * be called on that event.
	 * If the event is only stored OR passed through, this is not necessary
	 * (as the plugin already has 1 implicit reference).
	 *
	 * The host guarantees that this function is realtime safe if the 
	 * plugin is.
	 *
	 * @param event An event received at an input that will be copied to
         *              more than one output or duplicated in some other way.
	 * 
	 * PLUGINS THAT VIOLATE THESE RULES MAY CAUSE CRASHES AND MEMORY LEAKS.
	 */
	uint32_t (*lv2_event_ref)(LV2_Event_Callback_Data callback_data,
	                          LV2_Event*              event);
	
	/** Drop a reference to a non-POD event.
	 *
	 * If a plugin receives an event with type 0, it means the event is a
	 * pointer to some object in memory and not a flat sequence of bytes
	 * in the buffer.  If the plugin does not pass the event through to
	 * an output or store it internally somehow, it MUST call this function
	 * on the event (more information on using non-POD events below).
	 *
	 * The host guarantees that this function is realtime safe if the 
         * plugin is.
	 *
	 * @param event An event received at an input that will not be copied to
	 *              an output or stored in any way.
	 *
	 * PLUGINS THAT VIOLATE THESE RULES MAY CAUSE CRASHES AND MEMORY LEAKS.
	 */
	uint32_t (*lv2_event_unref)(LV2_Event_Callback_Data callback_data,
	                            LV2_Event*              event);

} LV2_Event_Feature;


#endif // LV2_EVENT_H