A bunch of FlightIntegrator and VesselPrecalculate optimizations, mai…

…nly relevant in large part count situations. More can be done : I didn't touch yet stuff specific to aero situations (drag, conduction occlusion...) and there is probably something to be done about Integrate()

GameData/KSPCommunityFixes/Settings.cfg

@@ -420,6 +420,10 @@ KSP_COMMUNITY_FIXES
   // state synchronization and caching solar panels scaled space raycasts results.
   OptimizedModuleRaycasts = true
 
+  // General micro-optimization of FlightIntegrator and VesselPrecalculate, significantely increase
+  // framerate in large part count situations.
+  FlightPerf = true
+
   // ##########################
   // Modding
   // ##########################

KSPCommunityFixes/KSPCommunityFixes.csproj

@@ -139,6 +139,7 @@
     <Compile Include="Performance\DisableMapUpdateInFlight.cs" />
     <Compile Include="Performance\DragCubeGeneration.cs" />
     <Compile Include="Performance\FastLoader.cs" />
+    <Compile Include="Performance\FlightPerf.cs" />
     <Compile Include="Performance\IMGUIOptimization.cs" />
     <Compile Include="Performance\LocalizerPerf.cs" />
     <Compile Include="Performance\LowerMinPhysicsDTPerFrame.cs" />

KSPCommunityFixes/Library/Numerics.cs

@@ -1,4 +1,5 @@
-using System.Runtime.CompilerServices;
+using System;
+using System.Runtime.CompilerServices;
 using UnityEngine;
 
 namespace KSPCommunityFixes.Library
@@ -16,6 +17,48 @@ public static void Add(ref this Vector3d v, Vector3d other)
             v.z += other.z;
         }
 
+        /// <summary>
+        /// Return a QuaternionD representing a rotation from a Vector3d to another
+        /// </summary>
+        public static QuaternionD FromToRotation(Vector3d from, Vector3d to)
+        {
+            double d = Vector3d.Dot(from, to);
+            double qw = Math.Sqrt(from.sqrMagnitude * to.sqrMagnitude) + d;
+            double x, y, z, sqrMag;
+            if (qw < 1e-12)
+            {
+                // vectors are 180 degrees apart
+                x = from.x;
+                y = from.y;
+                z = -from.z;
+                sqrMag = x * x + y * y + z * z;
+                if (sqrMag != 1.0)
+                {
+                    double invNorm = 1.0 / Math.Sqrt(sqrMag);
+                    x *= invNorm;
+                    y *= invNorm;
+                    z *= invNorm;
+                }
+                return new QuaternionD(x, y, z, 0.0);
+            }
+
+            Vector3d axis = Vector3d.Cross(from, to);
+            x = axis.x;
+            y = axis.y;
+            z = axis.z;
+            sqrMag = x * x + y * y + z * z + qw * qw;
+            if (sqrMag != 1.0)
+            {
+                double invNorm = 1.0 / Math.Sqrt(sqrMag);
+                x *= invNorm;
+                y *= invNorm;
+                z *= invNorm;
+                qw *= invNorm;
+            }
+
+            return new QuaternionD(x, y, z, qw);
+        }
+
         /// <summary>
         /// Cast a Matrix4x4 to a Matrix4x4D
         /// </summary>
@@ -50,6 +93,15 @@ public static Vector3d MultiplyVector(ref this Matrix4x4D m, Vector3d vector)
                 m.m20 * vector.x + m.m21 * vector.y + m.m22 * vector.z);
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Vector3d MultiplyPoint3x4(ref this Matrix4x4D m, double x, double y, double z)
+        {
+            return new Vector3d(
+                m.m00 * x + m.m01 * y + m.m02 * z + m.m03,
+                m.m10 * x + m.m11 * y + m.m12 * z + m.m13,
+                m.m20 * x + m.m21 * y + m.m22 * z + m.m23);
+        }
+
         /// <summary>
         /// Evaluate whether a given integral value is a power of 2.
         /// </summary>