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Merge pull request #8366 from kencooke/master

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optimized distance-attnuation calculation
This commit is contained in:
Brad Hefta-Gaub 2016-08-05 16:45:35 -07:00 committed by GitHub
commit 7cbc0bcabe
1 changed files with 58 additions and 1 deletions
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59
assignment-client/src/audio/AudioMixer.cpp
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@ -100,6 +100,63 @@ AudioMixer::AudioMixer(ReceivedMessage& message) :
const float ATTENUATION_BEGINS_AT_DISTANCE = 1.0f;
const int IEEE754_MANT_BITS = 23;
const int IEEE754_EXPN_BIAS = 127;
//
// for x > 0.0f, returns log2(x)
// for x <= 0.0f, returns large negative value
//
// abs |error| < 8e-3, smooth (exact for x=2^N) for NPOLY=3
// abs |error| < 2e-4, smooth (exact for x=2^N) for NPOLY=5
// rel |error| < 0.4 from precision loss very close to 1.0f
//
static inline float fastlog2(float x) {
union { float f; int32_t i; } mant, bits = { x };
// split into mantissa and exponent
mant.i = (bits.i & ((1 << IEEE754_MANT_BITS) - 1)) | (IEEE754_EXPN_BIAS << IEEE754_MANT_BITS);
int32_t expn = (bits.i >> IEEE754_MANT_BITS) - IEEE754_EXPN_BIAS;
mant.f -= 1.0f;
// polynomial for log2(1+x) over x=[0,1]
//x = (-0.346555386f * mant.f + 1.346555386f) * mant.f;
x = (((-0.0821307180f * mant.f + 0.321188984f) * mant.f - 0.677784014f) * mant.f + 1.43872575f) * mant.f;
return x + expn;
}
//
// for -126 <= x < 128, returns exp2(x)
//
// rel |error| < 3e-3, smooth (exact for x=N) for NPOLY=3
// rel |error| < 9e-6, smooth (exact for x=N) for NPOLY=5
//
static inline float fastexp2(float x) {
union { float f; int32_t i; } xi;
// bias such that x > 0
x += IEEE754_EXPN_BIAS;
//x = MAX(x, 1.0f);
//x = MIN(x, 254.9999f);
// split into integer and fraction
xi.i = (int32_t)x;
x -= xi.i;
// construct exp2(xi) as a float
xi.i <<= IEEE754_MANT_BITS;
// polynomial for exp2(x) over x=[0,1]
//x = (0.339766028f * x + 0.660233972f) * x + 1.0f;
x = (((0.0135557472f * x + 0.0520323690f) * x + 0.241379763f) * x + 0.693032121f) * x + 1.0f;
return x * xi.f;
}
float AudioMixer::gainForSource(const PositionalAudioStream& streamToAdd,
const AvatarAudioStream& listeningNodeStream, const glm::vec3& relativePosition, bool isEcho) {
float gain = 1.0f;
@ -148,7 +205,7 @@ float AudioMixer::gainForSource(const PositionalAudioStream& streamToAdd,
g = (g > 1.0f) ? 1.0f : g;
// calculate the distance coefficient using the distance to this node
float distanceCoefficient = exp2f(log2f(g) * log2f(distanceBetween/ATTENUATION_BEGINS_AT_DISTANCE));
float distanceCoefficient = fastexp2(fastlog2(g) * fastlog2(distanceBetween/ATTENUATION_BEGINS_AT_DISTANCE));
// multiply the current attenuation coefficient by the distance coefficient
gain *= distanceCoefficient;