Add friction feature to motion tab

#344

src/tabcontrollers/MoveCenterTabController.cpp

@@ -464,6 +464,12 @@ int MoveCenterTabController::smoothTurnRate() const
         settings::IntSetting::PLAYSPACE_smoothTurnRate );
 }
 
+int MoveCenterTabController::frictionPercent() const
+{
+    return settings::getSetting(
+        settings::IntSetting::PLAYSPACE_frictionPercent );
+}
+
 void MoveCenterTabController::setSmoothTurnRate( int value, bool notify )
 {
     settings::setSetting( settings::IntSetting::PLAYSPACE_smoothTurnRate,
@@ -475,6 +481,17 @@ void MoveCenterTabController::setSmoothTurnRate( int value, bool notify )
     }
 }
 
+void MoveCenterTabController::setFrictionPercent( int value, bool notify )
+{
+    settings::setSetting( settings::IntSetting::PLAYSPACE_frictionPercent,
+                          value );
+
+    if ( notify )
+    {
+        emit frictionPercentChanged( value );
+    }
+}
+
 bool MoveCenterTabController::adjustChaperone() const
 {
     return settings::getSetting(
@@ -1929,12 +1946,6 @@ void MoveCenterTabController::gravityToggleAction(
 
 void MoveCenterTabController::gravityReverseAction( bool gravityReverseHeld )
 {
-    // detect new press or new release
-    if ( ( gravityReverseHeld && !m_gravityReversed )
-         || ( !gravityReverseHeld && m_gravityReversed ) )
-    {
-        setGravityStrength( gravityStrength() * -1.0f );
-    }
     m_gravityReversed = gravityReverseHeld;
 }
 
@@ -2374,6 +2385,50 @@ void MoveCenterTabController::updateHandTurn(
 
 void MoveCenterTabController::updateGravity()
 {
+    float currentGravity = gravityStrength();
+    if ( m_gravityReversed )
+    {
+        currentGravity *= -1.0f;
+    }
+    double secondsSinceLastGravityUpdate
+        = std::chrono::duration<double>( std::chrono::steady_clock::now()
+                                         - m_lastGravityUpdateTimePoint )
+              .count();
+
+    // apply friction
+    if ( frictionPercent() > 0 )
+    {
+        // if we have friction and all velocity components are less than
+        // halt speed, we stop.
+        if ( abs( m_velocity[0] ) < k_frictionHalt_mps
+             && abs( m_velocity[1] ) < k_frictionHalt_mps
+             && abs( m_velocity[2] ) < k_frictionHalt_mps )
+        {
+            m_velocity[0] = 0.0;
+            m_velocity[1] = 0.0;
+            m_velocity[2] = 0.0;
+        }
+        else
+        {
+            // frictionPercent() * 10 is scaler such that at 90fps we
+            // reduce from terminal velocity (50m/s) to about 1mm/s in 1
+            // second using 100% friction. This is an arbitrary scaler,
+            // but doing a more accurate job would require a performance
+            // hit of the math pow() function to an arbitrary exponent.
+            double frictionVelocityMultiplier
+                = ( 100.0
+                    - ( static_cast<double>( frictionPercent() * 10 )
+                        * secondsSinceLastGravityUpdate ) )
+                  / 100.0;
+            frictionVelocityMultiplier
+                = std::clamp( frictionVelocityMultiplier, 0.0, 1.0 );
+
+            m_velocity[0] *= frictionVelocityMultiplier;
+            m_velocity[1] *= frictionVelocityMultiplier;
+            m_velocity[2] *= frictionVelocityMultiplier;
+        }
+    }
+
     // prevent velocity underflow
     if ( std::isnan( m_velocity[0] ) )
     {
@@ -2405,23 +2460,18 @@ void MoveCenterTabController::updateGravity()
         m_velocity[2] = 0.0;
     }
 
-    double secondsSinceLastGravityUpdate
-        = std::chrono::duration<double>( std::chrono::steady_clock::now()
-                                         - m_lastGravityUpdateTimePoint )
-              .count();
-
     // are we falling?
     // note: up is negative y
-    // note: set to always fall if gravity reversed (strength < 0)
-    if ( ( m_offsetY < m_gravityFloor ) || ( gravityStrength() < 0 ) )
+    // note: set to always fall if gravity reversed (currentGravity < 0)
+    if ( ( m_offsetY < m_gravityFloor ) || ( currentGravity < 0 ) )
     {
         // check if we're about to land
-        // note: we don't land if gravity is reversed (strength < 0)
+        // note: we don't land if gravity is reversed (currentGravity < 0)
         if ( ( m_offsetY
                    + static_cast<float>( m_velocity[1]
                                          * secondsSinceLastGravityUpdate )
                >= m_gravityFloor )
-             && gravityStrength() >= 0 )
+             && currentGravity >= 0 )
         {
             // get ratio of how much from y velocity applied to overcome y
             // offset and get down to ground.
@@ -2462,7 +2512,7 @@ void MoveCenterTabController::updateGravity()
             // accelerate downward velocity for the next update
             // note: downward is positive y
             m_velocity[1] = m_velocity[1]
-                            + ( static_cast<double>( gravityStrength() )
+                            + ( static_cast<double>( currentGravity )
                                 * secondsSinceLastGravityUpdate );
             return;
         }