LibAudio: Replace log_pan with a constant power panning algoritm

This little functional change uses the most common algorithm for panning
audio, known as constant power panning. It makes it so that the total
output power (not directly the sample value, i.e. the peak) stays the
same no matter how the audio is panned.

1 files changed, 11 insertions, 7 deletions

diff --git a/Userland/Libraries/LibAudio/Sample.h b/Userland/Libraries/LibAudio/Sample.h
index 23faf6244a..50e3c84907 100644
--- a/Userland/Libraries/LibAudio/Sample.h
+++ b/Userland/Libraries/LibAudio/Sample.h
@@ -90,18 +90,22 @@ struct Sample {
         return new_frame;
     }
 
-    ALWAYS_INLINE Sample& log_pan(double const pan)
+    // Constant power panning
+    ALWAYS_INLINE Sample& pan(double const position)
     {
-        left *= linear_to_log(min(pan * -1 + 1.0, 1.0));
-        right *= linear_to_log(min(pan + 1.0, 1.0));
+        double const pi_over_2 = AK::Pi<double> * 0.5;
+        double const root_over_2 = AK::sqrt(2.0) * 0.5;
+        double const angle = position * pi_over_2 * 0.5;
+        left *= root_over_2 * (AK::cos(angle) - AK::sin(angle));
+        right *= root_over_2 * (AK::cos(angle) + AK::sin(angle));
         return *this;
     }
 
-    ALWAYS_INLINE Sample log_pan(double const pan) const
+    ALWAYS_INLINE Sample panned(double const position) const
     {
-        Sample new_frame { left, right };
-        new_frame.log_pan(pan);
-        return new_frame;
+        Sample new_sample { left, right };
+        new_sample.pan(position);
+        return new_sample;
     }
 
     constexpr Sample& operator*=(double const mult)