[Gambas-user] OpenAL (gb.openal) example code

[Kevin Fishburne]

On 08/23/2015 12:43 AM, Kevin Fishburne wrote:
>
> Okay, I found this code:
>
> https://hackage.haskell.org/package/OpenAL-1.4.0.1/docs/src/Sound-OpenAL-AL-Listener.html
>
> with perhaps this being the pertinent information in its comments:
>
> -- | 'orientation' contains an \"at\" vector and an \"up\" vector, where the
> -- \"at\" vector represents the \"forward\" direction of the listener
> and the
> -- orthogonal projection of the \"up\" vector into the subspace
> perpendicular to
> -- the \"at\" vector represents the \"up\" direction for the listener.
> OpenAL
> -- expects two vectors that are linearly independent. These vectors are not
> -- expected to be normalized. If the two vectors are linearly dependent,
> -- behavior is undefined. The initial orientation is ('Vector3' 0 0 (-1),
> -- 'Vector3' 0 1 0), i.e. looking down the Z axis with the Y axis pointing
> -- upwards.
>
> I changed the listener orientation vector assignment line to this:
>
> Al.Listenerfv(Al.ORIENTATION, [0, 0, -1, 0, 1, 0])
>
> and it seems to work with Al.SOURCE_RELATIVE set to FALSE for both
> listener and source position changes. Yummy. Let me know if any of this
> sounds correct and I'll continue testing/experimentation.
>

I now have OpenAL working well but I need to know how to change the 
orientation of the coordinate system to reflect that used by my game. 
Normally in a 3D game the X axis is left/right, the Y axis is 
up/down/elevation, and the Z axis goes into the screen (in/out). In 
Sylph the Y axis goes into the screen and the Z axis is 
up/down/elevation. As you move into the screen the Y coordinates 
decrease. An easy way to think about it is a piece of graph paper where 
the upper-left corner is X:0, Y:0 and the bottom-right corner is X:100, 
Y:100. You start at the bottom, facing the top, and move along the Y 
axis toward the top.

I believe that

Al.Listenerfv(Al.ORIENTATION, [0, 0, -1, 0, 1, 0])

orients the audio environment using the traditional axes and not mine 
where the Z and Y axes are switched. I have no idea how to calculate the 
proper values for this statement to reflect the axes used in Sylph.

Here's another explanation of how the two vectors in Al.Listenerfv work:

http://stackoverflow.com/questions/7861306/clarification-on-openal-listener-orientation

If the answer is obvious to anyone reading this, please clue me in.

-- 
Kevin Fishburne
Eight Virtues
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