[Openal-devel] AL_SOURCE_RELATIVE

[Daniel PEACOCK]

Hi Richard,

When you enable Source Relative mode on a  Source its Position, Velocity
and Orientation all become relative to the Listener's parameters rather
than absolute values.   It is as if the Listener is positioned at 0,0,0
with a velocity of 0,0,0 and an orientation of 0,0,-1,0,1,0 (at then up).
Changing the Listeners position, velocity, and orientation will have no
impact on a Source Relative Source.

>> If the listener is at <0,0,-100> and the source is at <0,0,-50> with
velocity <0,0,100>
>>and AL_SOURCE_RELATIVE is OFF, then the source is in front of the
listener, travelling
>>outwards.

Assuming the default orientation for the Listener (0,0,-1,0,1,0) the Source
is actually behind the listener and is travelling away from it.

>>If AL_SOURCE_RELATIVE is then switched on and this is equivalent to
setting
>>the listener to <0,0,0>, then the source goes behind the listener,
travelling inwards. Is this right?

With Relative Mode on, the Source is in-front of the listener and
travelling towards it.

Dan
Creative Labs, Inc.

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             "Richard Furse"                                               
             <rf015d9821 at bluey                                             
             onder.co.uk>                                               To 
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                                                                   Subject 
                                       [Openal-devel] AL_SOURCE_RELATIVE   
             03/29/2008 11:10                                              
             AM                                                            
                                                                           
                                                                           
                                                                           
                                                                           




Hi there - I'm a bit confused about what AL_SOURCE_RELATIVE is supposed to
do. Does it just pretend that the listener is at <0,0,0> for the rest of
processing? This is what I'd thought.


The annotated documentation for 1.0 says that:


        SOURCE_RELATIVE does not affect velocity or orientation
calculation.


However, the 1.1 spec says that this:


        … indicates that the position, velocity, cone and direction
properties of a source are to be interpreted relative to the listener
position.


Specifically:
      Should the listener orientation information be disabled when
      AL_SOURCE_RELATIVE is enabled? i.e. should the coordinate flip back
      to the default up=<0,1,0>, at=<0,0,-1>? I had guessed the answer here
      is no.
      Should the listener's velocity be modelled as zero for the rest of
      processing? I had guessed the answer here is no.
      If the listener is at <0,0,-100> and the source is at <0,0,-50> with
      velocity <0,0,100> and AL_SOURCE_RELATIVE is OFF, then the source is
      in front of the listener, travelling outwards. If AL_SOURCE_RELATIVE
      is then switched on and this is equivalent to setting the listener to
      <0,0,0>, then the source goes behind the listener, travelling
      inwards. Is this right?
      I'm guessing whatever rule applies for the velocities also applies to
      cone vectors etc.



Sorry if this is a FAQ...


--Richard _______________________________________________
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