dsound: Simplify the calculation of sound attenuation due to distance.

dlls/dsound/sound3d.c

@@ -53,8 +53,6 @@
 #include "dsdriver.h"
 #include "dsound_private.h"
 
-/* default intensity level for human ears */
-#define DEFAULT_INTENSITY 0.000000000001f
 /* default velocity of sound in the air */
 #define DEFAULT_VELOCITY 340
 
@@ -167,9 +165,6 @@ void DSOUND_Calc3DBuffer(IDirectSoundBufferImpl *dsb)
 {
 	/* volume, at which the sound will be played after all calcs. */
 	D3DVALUE lVolume = 0;
-	/* intensity (used for distance related stuff) */
-	double flIntensity;
-	double flTemp;
 	/* stuff for distance related stuff calc. */
 	D3DVECTOR vDistance;
 	D3DVALUE flDistance = 0;
@@ -223,16 +218,8 @@ void DSOUND_Calc3DBuffer(IDirectSoundBufferImpl *dsb)
 	if (flDistance < dsb->ds3db_ds3db.flMinDistance)
 		flDistance = dsb->ds3db_ds3db.flMinDistance;
 	
-	/* the following formula is taken from my physics book. I think it's ok for the *real* world...i hope m$ does it that way */
-	lVolume += 10000; /* ms likes working with negative volume...i don't */
-	lVolume /= 1000; /* convert hundreths of dB into B */
-	/* intensity level (loudness) = log10(Intensity/DefaultIntensity)...therefore */
-	flIntensity = pow(10,lVolume)*DEFAULT_INTENSITY;	
-	flTemp = (flDistance/dsb->ds3db_ds3db.flMinDistance)*(flDistance/dsb->ds3db_ds3db.flMinDistance);
-	flIntensity /= flTemp;
-	lVolume = log10(flIntensity/DEFAULT_INTENSITY);
-	lVolume *= 1000; /* convert back to hundreths of dB */
-	lVolume -= 10000; /* we need to do it in ms way */
+	/* attenuation proportional to the distance squared, converted to millibels as in lVolume*/
+	lVolume -= log10(flDistance/dsb->ds3db_ds3db.flMinDistance * flDistance/dsb->ds3db_ds3db.flMinDistance)*1000;
 	TRACE("dist. att: Distance = %f, MinDistance = %f => adjusting volume %d to %f\n", flDistance, dsb->ds3db_ds3db.flMinDistance, dsb->ds3db_lVolume, lVolume);
 
 	/* conning */