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-rw-r--r--Alc/panning.c27
1 files changed, 18 insertions, 9 deletions
diff --git a/Alc/panning.c b/Alc/panning.c
index bfdd47e2..619b89c6 100644
--- a/Alc/panning.c
+++ b/Alc/panning.c
@@ -143,17 +143,26 @@ void CalcDirectionCoeffs(const ALfloat dir[3], ALfloat spread, ALfloat coeffs[MA
* angle spread. See:
* http://www.ppsloan.org/publications/StupidSH36.pdf - Appendix A3
*
- * The gain of the source is compensated for size, so that the
- * loundness doesn't depend on the spread.
+ * When adjusted for N3D normalization instead of SN3D, these
+ * calculations are:
+ *
+ * ZH0 = -sqrt(pi) * (-1+ca);
+ * ZH1 = 0.5*sqrt(pi) * sa*sa;
+ * ZH2 = -0.5*sqrt(pi) * ca*(-1+ca)*(ca+1);
+ * ZH3 = -0.125*sqrt(pi) * (-1+ca)*(ca+1)*(5*ca*ca - 1);
+ * ZH4 = -0.125*sqrt(pi) * ca*(-1+ca)*(ca+1)*(7*ca*ca - 3);
+ * ZH5 = -0.0625*sqrt(pi) * (-1+ca)*(ca+1)*(21*ca*ca*ca*ca - 14*ca*ca + 1);
*
- * ZH0 = (-sqrt_pi * (-1.f + ca));
- * ZH1 = ( 0.5f*sqrtf(3.f)*sqrt_pi * sa*sa);
- * ZH2 = (-0.5f*sqrtf(5.f)*sqrt_pi * ca*(-1.f+ca)*(ca+1.f));
- * ZH3 = (-0.125f*sqrtf(7.f)*sqrt_pi * (-1.f+ca)*(ca+1.f)*(5.f*ca*ca-1.f));
- * solidangle = 2.f*F_PI*(1.f-ca)
- * size_normalisation_coef = 1.f/ZH0;
+ * The gain of the source is compensated for size, so that the
+ * loundness doesn't depend on the spread. That is, the factors are
+ * scaled so that ZH0 remains 1 regardless of the spread. Thus:
*
- * This is then adjusted for N3D normalization over SN3D.
+ * ZH0 = 1.0f;
+ * ZH1 = 0.5f * (ca+1.0f);
+ * ZH2 = 0.5f * (ca+1.0f)*ca;
+ * ZH3 = 0.125f * (ca+1.0f)*(5.0f*ca*ca - 1.0f);
+ * ZH4 = 0.125f * (ca+1.0f)*(7.0f*ca*ca - 3.0f)*ca;
+ * ZH5 = 0.0625f * (ca+1.0f)*(21.0f*ca*ca*ca*ca - 14.0f*ca*ca + 1.0f);
*/
ALfloat ca = cosf(spread * 0.5f);