1 files changed, 95 insertions, 0 deletions
diff --git a/core/mixer.cpp b/core/mixer.cpp
new file mode 100644
index 00000000..066c57bd
--- /dev/null
+++ b/core/mixer.cpp
@@ -0,0 +1,95 @@
+
+#include "config.h"
+
+#include "mixer.h"
+
+#include <cmath>
+
+#include "alnumbers.h"
+#include "devformat.h"
+#include "device.h"
+#include "mixer/defs.h"
+
+struct CTag;
+
+
+MixerOutFunc MixSamplesOut{Mix_<CTag>};
+MixerOneFunc MixSamplesOne{Mix_<CTag>};
+
+
+std::array<float,MaxAmbiChannels> CalcAmbiCoeffs(const float y, const float z, const float x,
+    const float spread)
+{
+    std::array<float,MaxAmbiChannels> coeffs{CalcAmbiCoeffs(y, z, x)};
+
+    if(spread > 0.0f)
+    {
+        /* Implement the spread by using a spherical source that subtends the
+         * angle spread. See:
+         * http://www.ppsloan.org/publications/StupidSH36.pdf - Appendix A3
+         *
+         * 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);
+         *
+         * The gain of the source is compensated for size, so that the
+         * loudness doesn't depend on the spread. Thus:
+         *
+         * 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);
+         */
+        const float ca{std::cos(spread * 0.5f)};
+        /* Increase the source volume by up to +3dB for a full spread. */
+        const float scale{std::sqrt(1.0f + al::numbers::inv_pi_v<float>/2.0f*spread)};
+
+        const float ZH0_norm{scale};
+        const float ZH1_norm{scale * 0.5f * (ca+1.f)};
+        const float ZH2_norm{scale * 0.5f * (ca+1.f)*ca};
+        const float ZH3_norm{scale * 0.125f * (ca+1.f)*(5.f*ca*ca-1.f)};
+
+        /* Zeroth-order */
+        coeffs[0]  *= ZH0_norm;
+        /* First-order */
+        coeffs[1]  *= ZH1_norm;
+        coeffs[2]  *= ZH1_norm;
+        coeffs[3]  *= ZH1_norm;
+        /* Second-order */
+        coeffs[4]  *= ZH2_norm;
+        coeffs[5]  *= ZH2_norm;
+        coeffs[6]  *= ZH2_norm;
+        coeffs[7]  *= ZH2_norm;
+        coeffs[8]  *= ZH2_norm;
+        /* Third-order */
+        coeffs[9]  *= ZH3_norm;
+        coeffs[10] *= ZH3_norm;
+        coeffs[11] *= ZH3_norm;
+        coeffs[12] *= ZH3_norm;
+        coeffs[13] *= ZH3_norm;
+        coeffs[14] *= ZH3_norm;
+        coeffs[15] *= ZH3_norm;
+    }
+
+    return coeffs;
+}
+
+void ComputePanGains(const MixParams *mix, const float*RESTRICT coeffs, const float ingain,
+    const al::span<float,MaxAmbiChannels> gains)
+{
+    auto ambimap = mix->AmbiMap.cbegin();
+
+    auto iter = std::transform(ambimap, ambimap+mix->Buffer.size(), gains.begin(),
+        [coeffs,ingain](const BFChannelConfig &chanmap) noexcept -> float
+        { return chanmap.Scale * coeffs[chanmap.Index] * ingain; }
+    );
+    std::fill(iter, gains.end(), 0.0f);
+}