[Openal-devel] Re: Distance units

[pclare at sensaura.creative.com]

James Tomaschke <james at infosemi.com> wrote on 15/03/2005 00:45:03:
> 2) Near field effects (e.g. Sensaura's MacroFX).  Since this relates to
> actual human head sizes we have to know the units.
>
> 3) Air absorption.  This could be expressed unit-free -- but then it
makes
> it difficult to have standard reverb presets (assuming air absorption is
> part of the preset).
>
> 4) Multi-speaker HRTF processing.  Arguable whether this is necessary,
but
> at Sensaura we chose to use absolute distance information in the
> implementation of our MultiDrive algorithm.
>
> AL does not spec these out.  However, a vendor could add such support as
an
> extension, along with a distance unit specifier.  I think the proper
route would be to:
>   1. Let implementors create extensions to features not defined in the AL
spec.
>   2. Review and discuss them for the next AL spec.

Item 3 (air absorption) might be considered a candidate for an extension,
but items 2 and 4 are basic 3D rendering gain calculations.  The core API
should allow for such rendering without forcing the use of extensions.  It
would be alsmost like saying, for a graphics library, that core
functionality would let you draw a line from point A to point B on the
screen but that to make the line blue you must use an extension.


> Extensions are a good way to test ideas out before adding them into
stone.
> OpenGL has had very important features like multitexturing for quite some
time
> for it was adopted into the GL spec.  Let's see some HRTF extensions in
1.1..
> give the community time to work with it and give some feedback before we
> require every implementation to adopt it.

I don't disagree with the basic philosphy here and if we weren't currently
revising the spec that would be the way to go but since we now have a
chance of fixing things for the better we should sieze the opportunity.


> I would like to see more on the features you described, is there any way
to
> get them posted on:
> http://www.openal.org/extensions.html

MacroFX & MultiDrive are covered in various white papers on the Sensaura
web site.

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