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

[Kevin Fishburne]

On 09/07/2015 01:42 AM, Kevin Fishburne wrote:
>
> 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.

I've only tested this on a 2.0 (stereo) audio setup, so there is some 
chance that the front and rear speakers will be reversed, but these are 
the two sets of values for the listener orientation for the two 
coordinate orientations I mentioned.

For a game where the Z axis goes "into" the screen and the Y axis is 
height/elevation (the normal way things are done), this works:

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

For a game where the Y axis goes "into" the screen and the Z axis is 
height/elevation (what Sylph uses), this works:

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

In a game where the camera's orientation is completely arbitrary (an FPS 
or flight sim, for example) the listener orientation should correspond 
to the "camera" orientation.

Something else to note about OpenAL is that if a sample/sound file is 
multichannel (stereo, for example) 3D positioning and doppler effects 
will be ignored and the sound will play equally on all speakers (like 
you were playing music in a media player). If you want a sound effect to 
use 3D positioning and doppler effects it must be mono (one channel). 
You can use a program like Audacity to check/correct this.

-- 
Kevin Fishburne
Eight Virtues
www: http://sales.eightvirtues.com
e-mail: sales at ...1887...
phone: (770) 853-6271