MetaMessage


1   /*
2    * @(#)MetaMessage.java 1.24 03/12/19
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package javax.sound.midi;
9   
10  import java.io.ByteArrayOutputStream  ;
11  import java.io.DataOutputStream  ;
12  import java.io.IOException  ;
13  
14  
15  /**
16   * A <code>MetaMessage</code> is a <code>{@link MidiMessage}</code> that is not meaningful to synthesizers, but
17   * that can be stored in a MIDI file and interpreted by a sequencer program.
18   * (See the discussion in the <code>MidiMessage</code>
19   * class description.)  The Standard MIDI Files specification defines
20   * various types of meta-events, such as sequence number, lyric, cue point,
21   * and set tempo.  There are also meta-events
22   * for such information as lyrics, copyrights, tempo indications, time and key
23   * signatures, markers, etc.  For more information, see the Standard MIDI Files 1.0
24   * specification, which is part of the Complete MIDI 1.0 Detailed Specification
25   * published by the MIDI Manufacturer's Association
26   * (<a href = http://www.midi.org>http://www.midi.org</a>).
27   *
28   * <p>
29   * When data is being transported using MIDI wire protocol,
30   * a <code>{@link ShortMessage}</code> with the status value <code>0xFF</code> represents
31   * a system reset message.  In MIDI files, this same status value denotes a <code>MetaMessage</code>.
32   * The types of meta-message are distinguished from each other by the first byte
33   * that follows the status byte <code>0xFF</code>.  The subsequent bytes are data
34   * bytes.  As with system exclusive messages, there are an arbitrary number of
35   * data bytes, depending on the type of <code>MetaMessage</code>.
36   *
37   * @see MetaEventListener
38   *
39   * @version 1.24, 03/12/19
40   * @author David Rivas
41   * @author Kara Kytle
42   */
43  
44  public class MetaMessage extends MidiMessage   {
45  
46  
47      // Status byte defines
48  
49      /**
50       * Status byte for <code>MetaMessage</code> (0xFF, or 255), which is used
51       * in MIDI files.  It has the same value as SYSTEM_RESET, which
52       * is used in the real-time "MIDI wire" protocol.
53       * @see MidiMessage#getStatus
54       */
55      public static final int META                        = 0xFF; // 255
56  
57  
58      // Default meta message data: just the META status byte value
59      // $$kk: 09.09.99: need a real event here!!
60  
61      private static byte[] defaultMessage                = { (byte)META, 0 };
62  
63  
64  
65      // Instance variables
66  
67      /**
68       * The length of the actual message in the data array.
69       * This is used to determine how many bytes of the data array
70       * is the message, and how many are the status byte, the
71       * type byte, and the variable-length-int describing the
72       * length of the message.
73       */
74      private int dataLength = 0;
75  
76  
77      /**
78       * Constructs a new <code>MetaMessage</code>. The contents of
79       * the message are not set here; use
80       * {@link #setMessage(int, byte[], int) setMessage}
81       * to set them subsequently.
82       */
83      public MetaMessage() {
84      //super(defaultMessage);
85      this(defaultMessage);
86      }
87  
88  
89      /**
90       * Constructs a new <code>MetaMessage</code>.
91       * @param data an array of bytes containing the complete message.
92       * The message data may be changed using the <code>setMessage</code>
93       * method.
94       * @see #setMessage
95       */
96      protected MetaMessage(byte[] data) {
97      super(data);
98      //$$fb 2001-10-06: need to calculate dataLength. Fix for bug #4511796
99      if (data.length>=3) {
100         dataLength=data.length-3;
101         int pos=2;
102         while (pos<data.length && (data[pos] & 0x80)!=0) {
103         dataLength--; pos++;
104         }
105     }
106     }
107 
108 
109     /**
110      * Sets the message parameters for a <code>MetaMessage</code>.
111      * Since only one status byte value, <code>0xFF</code>, is allowed for meta-messages,
112      * it does not need to be specified here.  Calls to <code>{@link MidiMessage#getStatus getStatus}</code> return
113      * <code>0xFF</code> for all meta-messages.
114      * <p>
115      * The <code>type</code> argument should be a valid value for the byte that
116      * follows the status byte in the <code>MetaMessage</code>.  The <code>data</code> argument
117      * should contain all the subsequent bytes of the <code>MetaMessage</code>.  In other words,
118      * the byte that specifies the type of <code>MetaMessage</code> is not considered a data byte.
119      *
120      * @param type      meta-message type (must be less than 128)
121      * @param data      the data bytes in the MIDI message
122      * @param length    the number of bytes in the <code>data</code>
123      * byte array
124      * @throws          <code>InvalidMidiDataException</code>  if the
125      * parameter values do not specify a valid MIDI meta message
126      */
127     public void setMessage(int type, byte[] data, int length) throws InvalidMidiDataException   {
128 
129     if (type >= 128 || type < 0) {
130         throw new InvalidMidiDataException  ("Invalid meta event with type " + type);
131     }
132     if ((length > 0 && length > data.length) || length < 0) {
133         throw new InvalidMidiDataException  ("length out of bounds: "+length);
134     }
135     
136     this.length = 2 + getVarIntLength(length) + length;
137     this.dataLength = length;
138     this.data = new byte[this.length];
139     this.data[0] = (byte) META;        // status value for MetaMessages (meta events)
140     this.data[1] = (byte) type;        // MetaMessage type
141     writeVarInt(this.data, 2, length); // write the length as a variable int
142     if (length > 0) {
143         System.arraycopy(data, 0, this.data, this.length - this.dataLength, this.dataLength);
144     }
145     }
146 
147 
148     /**
149      * Obtains the type of the <code>MetaMessage</code>.
150      * @return an integer representing the <code>MetaMessage</code> type
151      */
152     public int getType() {
153     if (length>=2) {
154         return data[1] & 0xFF;
155     }
156     return 0;
157     }
158 
159 
160 
161     /**
162      * Obtains a copy of the data for the meta message.  The returned
163      * array of bytes does not include the status byte or the message
164      * length data.  The length of the data for the meta message is
165      * the length of the array.  Note that the length of the entire
166      * message includes the status byte and the meta message type
167      * byte, and therefore may be longer than the returned array.
168      * @return array containing the meta message data.
169      * @see MidiMessage#getLength
170      */
171     public byte[] getData() {
172     byte[] returnedArray = new byte[dataLength];
173     System.arraycopy(data, (length - dataLength), returnedArray, 0, dataLength);
174     return returnedArray;
175     }
176 
177 
178     /**
179      * Creates a new object of the same class and with the same contents
180      * as this object.
181      * @return a clone of this instance
182      */
183     public Object   clone() {
184     byte[] newData = new byte[length];
185     System.arraycopy(data, 0, newData, 0, newData.length);
186 
187     MetaMessage   event = new MetaMessage  (newData);
188     return event;
189     }
190 
191     // HELPER METHODS
192 
193     private int getVarIntLength(long value) {
194     int length = 0;
195     do {
196         value = value >> 7;
197         length++;
198     } while (value > 0);
199     return length;
200     }
201     
202     private final static long mask = 0x7F;
203 
204     private void writeVarInt(byte[] data, int off, long value) {
205         int shift=63; // number of bitwise left-shifts of mask
206         // first screen out leading zeros
207         while ((shift > 0) && ((value & (mask << shift)) == 0)) shift-=7;
208         // then write actual values
209         while (shift > 0) {
210         data[off++]=(byte) (((value & (mask << shift)) >> shift) | 0x80);
211         shift-=7;
212         }
213         data[off] = (byte) (value & mask);
214     }
215 
216 }
217
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