From fa839e3fc9b92a4642d50c28bc607eb97e9ac1df Mon Sep 17 00:00:00 2001
From: Tom Brazier <tom_github@firstsolo.net>
Date: Sat, 10 Jun 2023 16:59:18 +0100
Subject: Change to a quadratic curve for alpha and use a scale where 3 * drift
 speed results in alpha == 1.0

---
 filter-nm/ftnoir_filter_nm.cpp        | 10 ++++++----
 filter-nm/ftnoir_filter_nm.h          |  8 ++++----
 filter-nm/ftnoir_nm_filtercontrols.ui |  4 ++--
 3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/filter-nm/ftnoir_filter_nm.cpp b/filter-nm/ftnoir_filter_nm.cpp
index 5d274790..b222184b 100644
--- a/filter-nm/ftnoir_filter_nm.cpp
+++ b/filter-nm/ftnoir_filter_nm.cpp
@@ -42,17 +42,19 @@ void filter_nm::filter(const double* input, double* output)
         const double pos_tau = 1. / *s.pos_responsiveness;
         double alpha = dt / (dt + pos_tau);
         last_pos_speed += (pos_speed - last_pos_speed) * alpha;
-        alpha *= min(1.0, VectorLength(last_pos_speed) / *s.pos_drift_speed);
+        const double factor_pos = min(1.0, VectorLength(last_pos_speed) / (*s.pos_drift_speed * 3.0));
+        alpha *= factor_pos * factor_pos;
         last_pos_out += (position - last_pos_out) * alpha;
 
         const tQuat rot_delta = QuatDivide(rotation, last_rot_in);
-        const double ms_per_s = 1000.0;             // angular speed quaternions need to be small to work so use °/ms
-        const tQuat rot_speed = Slerp(tQuat(), rot_delta, 1.0 / dt / ms_per_s);
+        constexpr double ms_per_s = 1000.0;             // angular speed quaternions need to be small to work so use °/ms
+        const tQuat rot_speed = Slerp(tQuat(), rot_delta, 1.0 / ms_per_s / dt );
         const double rot_tau = 1. / *s.rot_responsiveness;
         alpha = dt / (dt + rot_tau);
         last_rot_speed = Slerp(last_rot_speed, rot_speed, alpha);
         const double angular_speed = AngleBetween(tQuat(), last_rot_speed) * ms_per_s;
-        alpha *= min(1.0, angular_speed / *s.rot_drift_speed);
+        const double factor_rot = min(1.0, angular_speed / (*s.rot_drift_speed * 3.0));
+        alpha *= factor_rot * factor_rot;
         last_rot_out = Slerp(last_rot_out, rotation, alpha);
     }
 
diff --git a/filter-nm/ftnoir_filter_nm.h b/filter-nm/ftnoir_filter_nm.h
index 7bf012a6..84775207 100644
--- a/filter-nm/ftnoir_filter_nm.h
+++ b/filter-nm/ftnoir_filter_nm.h
@@ -24,10 +24,10 @@ struct settings_nm : opts
 
     settings_nm() :
         opts("nm-filter"),
-        pos_responsiveness(value<slider_value>(b, "pos-responsiveness", { 15.0, .0, 20.0 })),
-        rot_responsiveness(value<slider_value>(b, "rot-responsiveness", { 18.0, .0, 20.0 })),
-        pos_drift_speed(value<slider_value>(b, "pos-drift-speed", { 30.0, 1.0, 200.0 })),
-        rot_drift_speed(value<slider_value>(b, "rot-drift-speed", { 45.0, 1.0, 400.0 }))
+        pos_responsiveness(value<slider_value>(b, "pos-responsiveness", { 13.0, .0, 20.0 })),
+        rot_responsiveness(value<slider_value>(b, "rot-responsiveness", { 16.0, .0, 20.0 })),
+        pos_drift_speed(value<slider_value>(b, "pos-drift-speed", { 5.0, 0.1, 50.0 })),
+        rot_drift_speed(value<slider_value>(b, "rot-drift-speed", { 7.0, 0.1, 50.0 }))
     {
     }
 };
diff --git a/filter-nm/ftnoir_nm_filtercontrols.ui b/filter-nm/ftnoir_nm_filtercontrols.ui
index ad307daf..7e317e74 100644
--- a/filter-nm/ftnoir_nm_filtercontrols.ui
+++ b/filter-nm/ftnoir_nm_filtercontrols.ui
@@ -171,7 +171,7 @@
          <number>1</number>
         </property>
         <property name="maximum">
-         <number>400</number>
+         <number>500</number>
         </property>
         <property name="orientation">
          <enum>Qt::Horizontal</enum>
@@ -220,7 +220,7 @@
          <number>1</number>
         </property>
         <property name="maximum">
-         <number>200</number>
+         <number>500</number>
         </property>
         <property name="orientation">
          <enum>Qt::Horizontal</enum>
-- 
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