
    <chapter id="oal-operation">
    <title>&OAL; Operation</title>

     <sect1>
     <title>&OAL; Fundamentals</title>
     <para>
       &OAL; (henceforth, the "&AL;") is concerned only with rendering audio 
       into an output buffer,
       and primarily meant for spatialized audio.
       There is no support for reading audio input from buffers at this
       time, and no support for MIDI and other components usually
       associated with audio hardware. Programmers must relay on other
       mechanisms to obtain audio (e.g. voice) input or generate music.
     </para>
     <para>
       The &AL; has three fundamental primitives or objects -- Buffers, Sources, 
       and a single Listener. Each object can be changed independently,
       the setting of one object does not affect the setting of others.
       The application can also set modes that affect processing. Modes
       are set, objects specified, and other &AL; operations performed
       by sending commands in the form of function or procedure calls. 
     </para><para>
       Sources store locations, directions, and other attributes of an object in 3D
       space and have a buffer associated with them for playback.  There are
       normally far more sources defined than buffers. When the program wants to play
       a sound, it controls execution through a source object. Sources are
       processed independently from each other.
    </para><para>
       Buffers store compressed or un-compressed audio data.  It is common to
       initialize a large set of buffers when the program first starts (or at
       non-critical times during execution -- between levels in a game, for instance).
       Buffers are referred to by Sources. Data (audio sample data) is associated
       with buffers. 
     </para><para>
       There is only one listener (per audio context).  The listener attributes are
       similar to source attributes, but are used to represent where the user is
       hearing the audio from.  The influence of all the sources from the
       perspective of the listener is mixed and played for the user.
    </para>
  
    <![ %RFC [
       <note id="rfc-bk000926-03"><title>RFC: Data Binding</title><para>  
         Have to specifiy when pointer arguments are dereferenced.
      </para></note>
    ]]>
     <sect2>
     <title>Primitive Types</title>
     <para>
        As &AL; is meant to allow for seamless integration with &OGL; code
        if needed, the &AL; primitive (scalar) data types mimic the
        &OGL; data types. Guaranteed minimum sizes are stated for &OGL;
        data types (see table 2.2 of the &OGL; 1.2 Specification), but 
        the actual choice of C datatype is left to the implementation. 
        All implementations on a given binary architecture, however, must 
        use a common definition of these datatypes. 
     </para>

     <![ %RFC [
      <note><title>RFC/000507:</title><para>
         ALlong/ALulong are omitted from the Linux OpenGL Base ABI,
         and the GL specification. Do we want to go ahead on this,
         or trail GL? Do we include non-i386 architectures to list
         sizes explicitely. I.e. do we make the ABI part of our
         mandate?
       </para></note>
     ]]>

    <para>
     Note that this table uses explicit AL prefixes for clarity,
     while they might be omitted from the rest of the document
     for brevity. GCC equivalents are given for IA32, i.e. a
     portable and widely available compiler on the most common
     target architecture. 
    <table>
    <title>&AL; Primitive Data Types</title>
    <tgroup cols="4" align="left" colsep=1 rowsep=1>
    <colspec colname=c1>
    <colspec colname=c2>
    <thead>
    <row>
       <entry>AL Type</>
       <entry>Description</>        
       <entry>GL Type</>  
       <entry>GCC IA32</entry>
    </row>
    </thead>
    <tbody>
    <row>
        <entry> ALboolean                            </entry>
        <entry> 8-bit boolean                        </entry>
        <entry> GLboolean                            </entry>
        <entry> unsigned char                        </entry>
    </row>
    <row>
        <entry> ALbyte                               </entry>
        <entry> signed 8-bit 2's-complement integer  </entry>
        <entry> GLbyte                               </entry>
        <entry> signed char                          </entry>
    </row>
    <row >
        <entry> ALubyte                              </entry>
        <entry> unsigned 8-bit integer               </entry>
        <entry> GLubyte                              </entry>
        <entry> unsigned char                        </entry>
    </row>
    <row>
        <entry> ALshort                              </entry>
        <entry> signed 16-bit 2's-complement integer </entry>
        <entry> GLshort                              </entry>
        <entry> short                                </entry>
    </row
    <row>
        <entry> ALushort                             </entry>
        <entry> unsigned 16-bit integer              </entry>
        <entry> GLushort                             </entry>
        <entry> unsigned short                       </entry>
    </row>
    <row>
        <entry> ALint                                </entry>
        <entry> signed 32-bit 2's-complement integer </entry>
        <entry> GLint                                </entry>
        <entry> int                                  </entry>
    </row>
    <row>
        <entry> ALuint                               </entry>
        <entry> unsigned 32-bit integer              </entry>
        <entry> GLuint                               </entry>
        <entry> unsigned int                         </entry>
    </row>
  <![ %RFC [
    <row>
        <entry> ALlong                               </entry>
        <entry> signed 64-bit 2's-complement integer </entry>
        <entry> n/a                                  </entry>
        <entry> long long                            </entry>
    </row>
    <row>
        <entry> ALulong                              </entry>
        <entry> unsigned 64-bit integer              </entry>
        <entry> n/a                                  </entry>
        <entry> unsigned long long                   </entry>
    </row>
  ]]>
    <row>
        <entry> ALsizei                              </entry>
        <entry> non-negative 32-bit binary integer size </entry>
        <entry> GLsizei                              </entry>
        <entry> int                                  </entry>
    </row>
    <row>
        <entry> ALenum                               </entry>
        <entry> enumerated 32-bit value              </entry>
        <entry> GLenum                               </entry>
        <entry> unsigned int                         </entry>
    </row>
    <row>
        <entry> ALbitfield                           </entry>
        <entry> 32 bit bitfield                      </entry>
        <entry> GLbitfield                           </entry>
        <entry> unsigned int                         </entry>
    </row>
    <row>
        <entry> ALfloat                              </entry>
        <entry> 32-bit IEEE754 floating-point        </entry>
        <entry> GLfloat                              </entry>
        <entry> float                                </entry>
    </row>
    <row>
        <entry> ALclampf                             </entry>
        <entry> Same as ALfloat, but in range [0, 1] </entry>
        <entry> GLclampf                             </entry>
        <entry> float                                </entry>
    </row>
    <row>
        <entry> ALdouble                             </entry>
        <entry> 64-bit IEEE754 floating-point        </entry>
        <entry> GLdouble                             </entry>
        <entry> double                               </entry>
    </row>
    <row>
        <entry> ALclampd                             </entry>
        <entry> Same as ALdouble, but in range [0, 1] </entry>
        <entry> GLclampd                             </entry>
        <entry> double                               </entry>
    </row>
    </tbody>
    </tgroup>
    </table>
    </para>


      
    <![ %Annote [
       <note><title>Annotation on Type Sizes</title><para>
         It would be desirable to guarantee the bit size of &AL; data
         types, but this might affect the mapping to &OGL; types
         for which the &OGL; specification only guarantees a minimum 
         size.
       </para></note>
       <note><title>Annotation on 64bit integral</title><para>
         It would be desirable to define ulong and long, but again
         we defer to &OGL; in this decision.
       </para></note>
       <note><title>Annotation on Enumeration</title><para>
         &enum; is not a C or C++ enumeration, but implemented as
         C preprocesor defines. This makes it easier to handle
         extensions to the &AL; namespace, in particular in
         dealing with delays in distributing updated reference 
         headers.
       </para></note>
    ]]>
    </sect2>
    <sect2>
     <title>Floating-Point Computation</title>
     <para>
       Any representable floating-point value is legal as input
       to a &AL; command that requires floating point data.
       The result of providing a value that is not a floating
       point number to such a command is unspecified, but must not
       lead to &AL; interruption or termination. In IEEE arithmetic,
       for example, providing a negative zero or a denormalized
       number to a GL command yields predictable results, while
       providing an NaN or infinity yields unspecified results.
     </para><para>
       Some calculations require division. In such cases (including
       implied divisions required by vector normalizations), a
       division by zero produces an unspecified result but must
       not lead to GL interruption or termination.
     </para>
    </sect2>
    </sect1>
     
    <sect1>
     <title>AL State</title>
     <para>
       The &AL; maintains considerable state. This documents enumerates
       each state variable and describes how each variable can be
       changed. For purposes of discussion, state variables are
       categorized somewhat arbitrarily by their function. For example,
       although we describe operations that the &AL; performs on the
       implied output buffer, the outbut buffer is not part of the
       &AL; state. Certain states of &AL; objects (e.g. buffer states
       with respect to queueing) are introduced for discussion purposes, 
       but not exposed through the API.
     </para>
    </sect1>

    <sect1>
     <title>AL Command Syntax</title>
     <para>
        &AL; commands are functions or procedures. Various groups of
        commands perform the same operation but differ in how
        arguments are supplied to them. To conveniently accomodate 
        this variation, we adopt the &OGL; nnotation for describing
        commands and their arguments. 
     </para>

     <![ %Annote [
      <note><title>Annotation (Not all types supported yet)</title><para>
          At this time &AL; does not support the full flexibility that
          &OGL; offers. Certain entry points are supported only for
          some data types. In general, &AL; tends to use less entry
          points, using setter commands that use the same tokens
          as the matching query commands.  
       </para></note>
    ]]>

    </sect1>

     <sect1>
     <title>Basic AL Operation</title>
     <para>
       &AL; can be used for a variety of audio playback tasks, and is an
       excellent complement to &OGL; for real-time rendering.  A programmer who is
       familiar with &OGL; will immediately notice the similarities between the
       two APIs in that they describe their 3D environments using similar methods.
     </para>
    <para>
       For an &OGL;/&AL; program, most of the audio programming will be in two
       places in the code: initialization of the program, and the rendering loop. 
       An &OGL;/&AL; program will typically contain a section where the graphics and 
       audio systems are initialized, although it may be spread into multiple functions.
       For OpenAL, initialization normally consists of creating a context, creating
       the initial set of buffers, loading the buffers with sample data, creating 
       sources, attaching buffers to sources, setting locations and directions for 
       the listener and sources, and setting the initial values for state global 
       to &AL;.
    </para>

  <example>
      <title>Initialization Example</title>
     <para>
          &sample.c;
     </para>
   <programlisting>    
  </programlisting>
       </example>

    <![ %Example [   
      <example>
      <title>Initialization Example</title>
      <programlisting>
      &ExInitAL.c;
       </programlisting>
       </example>
    ]]>

   <para>
      The audio update within
      the rendering loop normally consists of telling &AL; the current locations
      of the sources and listener, updating the environment settings, and managing
      buffers.
   </para>

    <![ %Example [
      <example>
      <title>Processing Loop</title>
      <programlisting>
// PlaceCamera -- places OpenGL camera and updates OpenAL listener position and source state
void 3DEnvironemnt:PlaceCamera()
{
   // update OpenGL camera position
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   glFrustum(-0.1333, 0.1333, -0.1, 0.1, 0.2, 50.0);

   gluLookAt(listenerPos[0], listenerPos[1], listenerPos[2],
      (listenerPos[0] + sin(listenerAngle)), listenerPos[1], (listenerPos[2] - cos(listenerAngle)),
      0.0, 1.0, 0.0);

   // OpenAL stuff...
   // place listener at camera
   alListener3f(AL_POSITION, listenerPos[0], listenerPos[1], listenerPos[2]);
   float directionvect[6];
   directionvect[0] = (float) sin(listenerAngle);
   directionvect[1] = 0;
   directionvect[2] = (float) cos(listenerAngle);
   directionvect[3] = 0;
   directionvect[4] = 1;
   directionvect[5] = 0;
   alListenerfv(AL_ORIENTATION, directionvect);

   // play phasor if in range, else stop playback
   if (range() < 9)
   {
      alSourcePlay(source[1]);
   } else
   {
      alSourceStop(source[1]);
   }
}       
       </programlisting>
       </example>
    ]]>

   </sect1>

     <sect1 id="errors">
     <title>AL Errors</title>
     <para>
       The AL detects only a subset of those conditions that could be
       considered errors. This is because in many cases error checking
       would adversely impact the performance of an error-free program.
       The command
      <funcsynopsis><funcprototype> 
      <funcdef> &enum; <function> GetError </function></funcdef>
      <void>
      </funcprototype></funcsynopsis>
      is used to obtain error information. Each detectable error is
      assigned a numeric code. When an error is detected by AL, 
      a flag is set and the error code is recorded. Further errors,
      if they occur, do not affect this recorded code. When GetError
      is called, the code is returned and the flag is cleared, so that
      a further error will again record its code. If a call to GetError
      returns NO_ERROR then there has been no detectable error since
      the last call to GetError (or since the AL was initialized).
     </para>
   
    <![ %RFC [
       <note id="rfc-bk000926-04"><title>RFC: GL distributed error </title><para>  
      To allow for distributed implementations there may be several
      flag/code pairs. In this case, after a call to GetError returns a
      value other than NO_ERROR each subsequent call returns the 
      non-NO_ERROR code of another distinct flag-code pair (in 
      unspecified order), until all NO_ERROR codes have been returned. 
      When there are no more non-NO_ERROR codes, all flags be reset.
      The initial state of all flags is cleared and the initial value
      of all codes is NO_ERROR.
     </para></note>
     <note><title>Annotation (Looping GetError)</title><para>
       &AL; applications are advised to loop calls of GetError to
       make sure that all flags are reset. Only the first error
       occurence for each flag/code pair is recorded, subsequent
       errors are ignored. The result of a repeated GetError call
       is not a stack trace or LIFO sequence. All error handling
       is context specific.

      </para></note>
    ]]>
    

    <![ %Annote [
      <note><title>Annotation (Only First Error)</title><para>
       Like &OGL; &AL; will ignore subsequent errors once an
       error conditation has been encountered.
      </para></note>
    ]]>

    <para>
      Error codes can be mapped to strings. The GetString function
      returns a pointer to a constant (literal) string that is 
      identical to the identifier used for the enumeration value,
      as defined in the specification. 
    </para>

    <![ %Annote [
      <note><title>Annotation/ Verbose Error String</title><para>
        There is no need to maintain a separate GetErrorString
        function (inspired by the proposed gluGetErrorStrings) 
        as the existing GetString entry point can be used.
      </para></note>
    ]]> 
   

    <para>
    <table>
    <title>Error Conditions</title>
    <tgroup cols="2" align="left" colsep=1 rowsep=1>
    <colspec colname=c1>
    <colspec colname=c2>
    <thead>
    <row>
       <entry>Name</>
       <entry>Description</>        
    </row>
    </thead>
    <tbody>
    <row>
       <entry>NO_ERROR</>
       <entry>"No Error" token.</>  
    </row>
    <row>
       <entry>INVALID_NAME</>
       <entry>Invalid Name parameter.</>  
    </row>
    <row>
       <entry>INVALID_ENUM</>
       <entry>Invalid parameter.</> 
    </row>
    <row>
       <entry>INVALID_VALUE</>
       <entry>Invalid enum parameter value.</>  
    </row>
    <row>
       <entry>INVALID_OPERATION</>
       <entry>Illegal call.</>  
    </row>
    <row>
       <entry>OUT_OF_MEMORY</>
       <entry>Unable to allocate memory.</>  
    </row>
    </tbody>
    </tgroup>
    </table>
      The table summarizes the AL errors. Currently, when an error flag
      is set, results of AL operations are undefined only if OUT_OF_MEMORY
      has occured. In other cases, the command generating the error is
      ignored so that it has no effect on AL state or output buffer
      contents. If the error generating command returns a value,
      it returns zero. If the generating command modifies values
      through a pointer argument, no change is made to these values.
      These error semantics apply only to AL errors, not to system errors
      such as memory access errors.
    </para>
    <para>
       Several error generation conditions are implicit in the description
       of the various AL commands. First, if a command that requires
       an enumerated value is passed a value that is not one of those
       specified as allowable for that command, the error INVALID_ENUM
       results. This is the case even if the argument is a pointer to
       a symbolic constant if that value is not allowable for the given 
       command.
       This will occur whether the value is allowable for other functions,
       or an invalid integer value.
    </para>
    <para>
       Integer parameters that are used as names for &AL; objects
       such as Buffers and Sources are checked for validity. If an invalid
       name parameter is specified in an &AL; command, an
       INVALID_NAME error will be generated, and the command is ignored.
    </para>
    <para>
       If a negative integer is provided where an argument of type
       &sizei; is specified, the error INVALID_VALUE results. The same
       error will result from attempts to set integral and floating
       point values for attributes exceeding the legal range for
       these. The specification does not guarantee that the implementation 
       emits INVALID_VALUE if a &NaN; or &Infty; value is 
       passed in for a &float; or &double; argument (as the specification 
       does not enforce possibly expensive testing of floating point
       values).
    </para>

   <para>
      Commands can be invalid. For example, certain commands might not be
      applicable to a given object. There are also illegal combinations
      of tokens and values as arguments to a command.  &AL; responds to any 
      such illegal command with an INVALID_OPERATION error.  
    </para>

     <![ %Scratch [
       <para>
         No longer true except for extensions. To be avoided
         in general:    &AL; has
         mutually exclusive commands operating on similar objects.
         One example is treating a streaming buffer as a 
         non-streaming buffer, another is appending data to a 
         non-streaming buffer. 
       </para>
    ]]>

    <para>
       If memory is exhausted as a side effect of the execution of an
       AL command, either on system level or by exhausting the allocated
       resources at AL's internal disposal, the error OUT_OF_MEMORY
       may be generated. This can also happen independent of recent
       commands if &AL; has to request memory for an internal task
       and fails to allocate the required memory from the operating
       system.
    </para>
    <para>
       Otherwise errors are generated only for conditions that are 
       explicitely described in this specification.
    </para>

   
    <![ %RFC [
       <note id="rfc-bk000807-01"><title>RFC: INVALID_SIZE?</title><para>  
           Specific error case in which the size argument is
           negative, or mismatches internal conditions for a getter?
      </para></note>
    ]]>


    <![ %RFC [
       <note id="rfc-bk000802-03"><title>RFC: INVALID_POINTER?</title><para>  
         GL seemingly does not specify a response to NULL pointer
         destinations, and does not assign an error case. INVALID_VALUE
         could be used, also we could introduce a separate INVALID_POINTER.
         Is there a good reason not to catch these cases? 
      </para></note>
    ]]>
   
  
    </sect1>



    <sect1 id="control">
    <title>Controlling AL Execution</title>
   <para>
     The application can temporarily disable certain AL capabilities 
     on a per Context basis. This allows the driver implementation 
     to optimize for certain subsets of operations.
      Enabling and disabling capabilities is handled using a function
      pair. 
      <funcsynopsis><funcprototype> 
      <funcdef> &void; <function> Enable </function></funcdef>
      <paramdef> &enum; <parameter> target </parameter></paramdef>      
      </funcprototype></funcsynopsis>
     <funcsynopsis><funcprototype> 
      <funcdef> &void; <function> Disable </function></funcdef>
      <paramdef> &enum; <parameter> target </parameter></paramdef>      
      </funcprototype></funcsynopsis>
     The application can also query whether a given capability is
     currently enabled or not.
      <funcsynopsis><funcprototype> 
      <funcdef> &bool; <function> IsEnabled </function></funcdef>
      <paramdef> &enum; <parameter> target </parameter></paramdef>      
      </funcprototype></funcsynopsis>
     If the token used to specify target is not legal,
     an  INVALID_ENUM error will be generated.
   </para>
   <para>
     At this time, this mechanism is not used. There are no valid
     targets.
    </para>
    <![ %Annote [
      <note><title>Annotation (Enable/Disable)</title><para>
          Currently, &AL; is controlled exploiting existing
          commands. For example, to disable sound output but
          not processing, the Listener can be muted setting
          GAIN to zero. Selecting NONE as the distance model
          disables distance attenuation. Setting DOPPLER_FACTOR
          to zero disables the Doppler Effect. A redundant
          mechanism to accomplish the same is not needed.
       </para></note>
    ]]>
 
    </sect1>

    <sect1 id="objects">
    <title>Object Paradigm</title>
    <para>
     &AL; is an object-oriented API, but it does not expose classes, structs,
     or other explicit data structures to the application. 
    </para>


    <sect2 id="object-overview-categories">
     <title>Object Categories</title>
    <para>
     &AL; has three primary categories of Objects: 
     <itemizedlist>
       <listitem>
       <para>
          one unique Listener per Context
       </para>
       </listitem>
       <listitem> 
       <para>
          multiple Buffers shared among Contexts
       </para>
       </listitem>
       <listitem> 
       <para>
          multiple Sources, each local to a Context
       </para>
       </listitem> 
     </itemizedlist>
     In the following, "{Object}" will stand for either Source, 
     Listener, or Buffer.    
    </para>
    </sect2>

    <sect2 id="object-overview-dynamic">
     <title>Static vs. Dynamic Objects</title>
    <para>
     The vast majority of &AL; objects are dynamic, and will be created
     on application demand. There are also &AL; objects that do not have 
     to be created, and can not be created, on application demand. 
     Currently, the Listener is the only such static object in &AL;. 

    </para>
    </sect2>

    <sect2>
     <title>Object Names</title>
    <para>
     Dynamic Objects are manipulated using an integer, which in 
     analogy to &OGL; is referred to as the object's "name". These 
     are of type unsigned integer (uint). Names can be valid
     beyond the lifetime of the context they were requested,
     if the objects in question can be shared among contexts.
     No guarantees or assumptions are 
     made in the specification about the precise values or their distribution,
     over the lifetime of the application. As objects might be shared
     Names are guaranteed to be 
     unique within a class of &AL; objects, but no guarantees are made
     across different classes of objects. Objects like the Listener that
     are unique (singletons) do not require, and do not have, an integer "name".
    </para>
    </sect2>


    <sect2>
    <title>Requesting Object Names</title>
    <para>
     &AL; provides calls to obtain Object Names. The application requests 
     a number of Objects of a given category using Gen{Object}s.
     If the number n of Objects requested is negative,
     an INVALID_VALUE error will caused. The actual values of the
     Names returned are implementation dependent. No guarantees on 
     range or value are made. Unlike &OGL; &OAL does not offer alternative 
     means to define (bind) a Name.
    </para>
    <para>
     Allocation of Object Names does not imply immediate allocation of
     resources or creation of Objects: the implementation is free to 
     defer this until a given Object is actually used in mutator calls. 
     The Names are written at the memory location specified by the caller.
      <funcsynopsis><funcprototype> 
      <funcdef> void <function> Gen{Object}s </function></funcdef>
      <paramdef> &sizei; <parameter> n </parameter></paramdef>
      <paramdef> &uint;* <parameter> objectNames </parameter></paramdef>
      </funcprototype></funcsynopsis>
    </para>
    <para>
      Requesting zero names is a legal NOP. Requesting a negative
      number of names causes an INVALID_VALUE error. 
      &AL; will respond with an OUT_OF_MEMORY if the application 
      requests too many objects. The specification does not guarantee
      that the &AL; implementation will allocate all resources
      needed for the actual objects at the time the names are
      reserved. In many cases (Buffers) this could only be
      implemented by worst case estimation. Allocation of names
      does not guarantee that all the named objects can actually
      be used.
    </para>


    <![ %Scratch [
    <note><para>
      We do not re-use Names under any circumstance. Do we require
      implementations throwing OUT_OF_MERMORY errors on allocation of
      Names? No - we don't even specify buffer sizes. Ambiguity - could
      an implementation throw OOM because of no names, or OOM because
      of a (worst case) estimate of object sizes? Do we need OUT_OF_NAMES?   
    </para></note>
    ]]>


    <![ %Scratch [
     <warning><para>
       The current headers include a sizei return parameter:
        "Returns the number of ids actually allocated."
       This violates the "failed commands are NOPs" design
       and introduces ambiguity in error handling, and has
       thus been changed breaking backwards compatibility.
     </para></warning>
     ]]>

    <![ %Annote [
      <note><title>Annotation (No application selected Names)</title><para>
           Unlike GL, applications are not free to choose Names, all
           Names have to be requested. Aside from possible benefits for
           the implementation, and avoidance of errors in projects
           that have many modules using the AL implementation (a problem
           encountered in GL, when the two generation mechanisms are
           mixed), this also leaves open the door to feed different
           kinds of objects by Name through the same API entry points. 
       </para></note>
    ]]>
 
    <![ %Annote [
      <note><title>Annotate (Negative/zero sizei)</title><para>
         The specification does not guarantee that sizei is an
         unsigned integer, but legal values have to be non-negative.
         However, requesting zero names is a legal NOP. 
      </para></note>
    ]]>

     <![ %RFC [
     <note id=rfc-bk000626-02><title>RFC: Resource Release Hint</title><para>
      Do we need a hint that resource release has to be done on DeleteXXX,
       instead of leaving this housekeeping to &AL;?
     </para></note>
     <note id=rfc-bk000626-03><title>RFC: Zero Name</title><para>
      Do we reserve the name "0"? &OGL; provides an alternative mechanism
      which lets the application pick texture names, which we discarded
      because it is prone to create error conditions when mixing both 
      approaches. As all our names are generated using GenXXXX, there
      is no real need to treat "0" special.
     </para></note>
     ]]>

   </sect2>


   <sect2>
   <title>Releasing Object Names</title>
   <para>
     &AL; provides calls to the application to release Object Names
     using Delete{Object}s, implicitly requesting deletion of the 
     Objects associated with the Names released. If the number n of Objects named 
     is negative, an INVALID_VALUE error will be caused.
     If one or more of the specified Names is not valid, an INVALID_NAME 
     error will be caused. Implementation behavior following any error 
     is undefined. 
   </para>
   <para>
     Once deleted (even if an error occured on deletion), the Names are 
     no longer valid for use with any &AL; function calls including
     calls to Delete{Objects}s. Any such use will cause an INVALID_NAME 
     error. 
   </para>
   <para>
     The &AL; implementation is free to defer actual release of 
     resources. Ideally, resources should be released as soon as
     possible, but no guarantees are made.
      <funcsynopsis><funcprototype> 
      <funcdef>&void;<function>Delete{Object}s</function></funcdef>
      <paramdef>&sizei;<parameter>n</parameter></paramdef>
      <paramdef>&uint;*<parameter>objectNames</parameter></paramdef>
      </funcprototype></funcsynopsis>
    </para>
   
    <![ %Annote [
      <note><title>Annotation</title><para>
      GenXXX and DeleteXXX can not reasonably be expected to be used 
      for controlling driver-side resource management from the
      application. A driver might never release a Source once allocated
      during the lifetime of the application.   
    </para></note>
    ]]>

    <![ %RFC [
       <note id="rfc-bk000724-18"><title>RFC: Deletion Errors</title><para>  
          chasan@acm.org:  
          What happens if an active source (or its associated buffer) is deleted? 
          The source should be stopped? Or the delete operation is invalid?
      </para></note>
    ]]>

   </sect2>


   <sect2>
   <title>Validating an Object Name</title>
   <para>
     &AL; provides calls to validate the Name of an Object.
     The application can verify whether an Object Name is valid
     using the Is{Object} query. There is no vector (array)
     version of this function as it defeats the purpose of
     unambiguous (in)valdiation. Returns &TRUE; if id is a
     valid Object Name, and &FALSE; otherwise. Object Names are 
     valid between request (Gen{Object}s) and release (Delete{Object}s).
     Is{Object} does not distinguish between invalid and deleted Names. 
      <funcsynopsis><funcprototype> 
      <funcdef>&bool;<function>Is{Object}</function></funcdef>
      <paramdef>&uint;<parameter>objectName</parameter></paramdef>
      </funcprototype></funcsynopsis>
    </para>
    <![ %RFC [
    <note><title>RFC/bk000504:</title><para>
      If zero is a valid name, this function will have to accept
      it without an actyual object (or only an internal dummy)
      being associated with it. I recommend that implementations
      never return "0" as an object name.
    </para></note>
    ]]>
   </sect2>


   <sect2>
   <title>Setting Object Attributes</title>
   <para>
     For &AL; Objects, calls to control their attributes are provided.
     These depend on the actual properties of a given Object
     Category. The precise API is discussed for each category,
     below. Each &AL; command affecting the state of
     a named Object is usually of the form 
      <funcsynopsis><funcprototype> 
      <funcdef> void <function> {Object}{n}{sifd}{v} </function></funcdef>
      <paramdef> &uint; <parameter> objectName </parameter></paramdef>
      <paramdef> &enum; <parameter> paramName </parameter></paramdef>
      <paramdef> &type; <parameter> values </parameter></paramdef>
      </funcprototype></funcsynopsis>
     In the case of unnamed (unique) Objects, the (integer) objectName 
     is omitted, as it is implied by the {Object} part of function name:
      <funcsynopsis><funcprototype> 
      <funcdef> void <function> {Object}{n}{sifd}{v} </function></funcdef>
      <paramdef> &enum; <parameter> paramName </parameter></paramdef>
      <paramdef> &type; <parameter> values </parameter></paramdef>
      </funcprototype></funcsynopsis>
     For example, the Listener3d command would not require an (integer)
     objectName argument.
   </para>
   <para>
      The objectName specifies the &AL; object affected by this call.
      Use of an invalid Name will cause an INVALID_NAME error. 
   </para>
   <para> 
      The Object's Attribute to be affected has to be named
      as paramName. &AL; parameters applicable to one category
      of Objects are not necessarily legal for another catetgory 
      of &AL; Objects. Specification of a parameter illegal for
      a given object will cause an INVALID_OPERATION error.  
    </para>
    <para>
      Not all possible values for a type will be legal for a 
      given objectName and parameterName. Use of an illegal value 
      or a NULL value pointer will cause an INVALID_VALUE error.
    </para>
    <para>
      Any command that causes an error is a NOP.
    </para>
   </sect2>

   <sect2>
   <title>Querying Object Attributes</title>
   <para>
     For named and for unique &AL; Objects, calls to query their
     current attributes are provided.
     These depend on the actual properties of a given Object
     Category. The performance of such queries is implementation
     dependent, no performance guarantees are made. The valid values for the 
     parameter paramName are identical to the ones legal for the complementing
     attribute setting function.
      <funcsynopsis><funcprototype> 
      <funcdef> void <function> Get{Object}{n}{sifd}{v} </function></funcdef>
      <paramdef> &uint; <parameter> objectName </parameter></paramdef>
      <paramdef> &enum; <parameter> paramName </parameter></paramdef>
      <paramdef> &type;* <parameter> destination </parameter></paramdef>
      </funcprototype></funcsynopsis>
     For unnamed unique Objects, the objectName is omitted as it is 
     implied by the function name:
      <funcsynopsis><funcprototype> 
      <funcdef> void <function> Get{Object}{n}{sifd}{v} </function></funcdef>
      <paramdef> &enum; <parameter> paramName </parameter></paramdef>
      <paramdef> &type;* <parameter> destination </parameter></paramdef>
      </funcprototype></funcsynopsis>
    </para>
    <para>
     The precise API is discussed for each category separately, below.
     Unlike their matching mutators, Query functions for non-scalar 
     properties (vectors etc.) are only available in array form.
   </para>
   <para>
     Use of an invalid Name will cause an INVALID_NAME error. 
     Specification of an illegal parameter type (token) will cause 
     an INVALID_ENUM error.  A call with a destination
     NULL pointer will be quietly ignored. The &AL; state will not 
     be affected by errors. In case of errors, destination memory 
     will not be changed.
    </para>
   </sect2>


   <sect2>
    <title>Object Attributes</title>

    <para>
      Attributes affecting the processing of sounds can be set for various
      &AL; Object categories, or might change as an effect of &AL; calls.
      The vast majority of these Object properties are specific to the
      &AL; Object category, in question, but some are applicable to two
      or more categories, and are listed separately.
    </para>
    <para>
      The general form in which this document describes parameters is
    <table>
    <title>{Object} Parameters</title>
    <tgroup cols="4" align="left" colsep=1 rowsep=1>
    <colspec colname=c1>
    <colspec colname=c2>
    <colspec colname=c3>
    <colspec colname=c4>
    <thead>
    <row>
       <entry>&Par;</>
       <entry>&Sig;</>
       <entry>&Val</>
       <entry>&Def;</>        
    </row>
    </thead>
    <tbody>
    <row>
       <entry>paramName</>
       <entry>T</>
       <entry> range or set </>
       <entry> scalar or n-tupel </>        
    </row>
    </tbody>
    </tgroup>
    </table>
    Description:
        The description specifies additional restrictions and details.
        paramName is given as the &AL; enum defined as its name.
        T can be a list of legal signatures, usually the array form
        as well as the flat (unfolded) form.
    </para>


    <![ %RFC [
     <note id="rfc-bk000626-04"><title>RFC: Initial (Default) State</title><para>
      The default state of objects will have to be specified here.
      There will be no commands that allow the application to set
      other defaults.
     </para></note>
     ]]>
    </sect2>
    </sect1>
    </chapter>

