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event.h

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/* lv2_event.h - C header file for the LV2 events extension.
 *
 * Copyright (C) 2006-2007 Lars Luthman <lars.luthman@gmail.com>
 * Copyright (C) 2008-2009 Dave Robillard <http://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> ('lv2ev').
 *
 * 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.
 * 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.
 */
00049 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 is a single
 * chunk of POD (plain old data), usually contained in a flat buffer
 * (see LV2_EventBuffer below).  Unless a required feature says otherwise,
 * hosts may assume a deep copy of an LV2 event can be created safely
 * using a simple:
 *
 * memcpy(ev_copy, ev, sizeof(LV2_Event) + ev->size);  (or equivalent)
 */
00065 typedef struct {

      /** The frames portion of timestamp.  The units used here can optionally be
       * set for a port (with the lv2ev:timeUnits property), 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).
       */
00072       uint32_t frames;

      /** The sub-frames portion of timestamp.  The units used here can
       * optionally be set for a port (with the lv2ev:timeUnits property),
       * otherwise this is 1/(2^32) of an audio frame.
       */
00078       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 above).  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.
       */
00095       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.
       */
00100       uint16_t size;

      /* size bytes of data follow here */

} LV2_Event;



/** A buffer of LV2 events (header only).
 *
 * Like events (which this contains) an event buffer is a single chunk of POD:
 * the entire buffer (including contents) can be copied with a single memcpy.
 * The first contained event begins sizeof(LV2_EventBuffer) bytes after
 * the start of this struct.
 *
 * After this header, the buffer 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 | ...
 */
00123 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).
       */
00130       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).
       */
00138       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.
       */
00160       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.
       */
00170       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.
       */
00176       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.
       */
00188       uint32_t size;

} LV2_Event_Buffer;


/** Opaque pointer to host data. */
00194 typedef void* LV2_Event_Callback_Data;


/** The data field of the LV2_Feature for this extension.
 *
 * To support this feature 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.
 */
00203 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.
       */
00210       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, 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).
       *
       * @param event An event received at an input that will not be copied to
       *              an output or stored in any way.
       * @param context The calling context.  (Like event types) this is a mapped
       *                URI, see lv2_context.h. Simple plugin with just a run()
       *                method should pass 0 here (the ID of the 'standard' LV2
       *                run context).  The host guarantees that this function is
       *                realtime safe iff @a context is realtime safe.
       *
       * 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).
       *
       * @param event An event received at an input that will not be copied to
       *              an output or stored in any way.
       * @param context The calling context.  (Like event types) this is a mapped
       *                URI, see lv2_context.h. Simple plugin with just a run()
       *                method should pass 0 here (the ID of the 'standard' LV2
       *                run context).  The host guarantees that this function is
       *                realtime safe iff @a context is realtime safe.
       *
       * 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


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