Optimise VectorLine camera projection for improved Map View performance

[Halbann]

Orbit rendering takes up a significant majority of the frame time with a large number of orbit lines visible in the Map View, which is mainly caused by camera projection done by VectorLine.

This patch improves performance by caching the camera's projection matrix multiplied with its view matrix once per frame, and replacing calls to different camera projection functions in VectorLine with our cached versions.

Will write a full description with some benchmarking results when the patch is more complete.

[gotmachine]

I would recommend validating your results by comparing them to the original method results.
You can gate that validation code behind a file level #if def, and use ULP based equality comparisons (Numerics.AlmostEqual(), with maybe an ULP of 5 in this this case), see an example here :

KSPCommunityFixes/KSPCommunityFixes/Performance/FlightIntegratorPerf.cs

Lines 684 to 729 in 93b57a1

	#if DEBUG_UPDATEAERO
	private static float kspcf_rb_AngularDrag;
	private static float kspcf_dynamicPressurekPa;
	private static Vector3 kspcf_dragVectorDir;
	private static float kspcf_dragScalar;
	private static Vector3 kspcf_liftForce;
	private static float kspcf_liftScalar;
	private static void FlightIntegrator_UpdateAerodynamics_DebugPrefix(FlightIntegrator __instance, Part part)
	{
	FlightIntegrator_UpdateAerodynamics_Override(__instance, part);
	kspcf_dynamicPressurekPa = (float)part.dynamicPressurekPa; // comparing as float since this is computed from floats
	kspcf_dragVectorDir = part.dragVectorDir;
	kspcf_dragScalar = part.dragScalar;
	kspcf_liftForce = part.DragCubes.LiftForce;
	kspcf_liftScalar = part.bodyLiftScalar;
	}
	private static void FlightIntegrator_UpdateAerodynamics_DebugPostfix(Part part)
	{
	float stock_rb_angularDrag = part.rb.IsNotNullOrDestroyed() ? part.rb.angularDrag : 0f;
	float stock_dynamicPressurekPa = (float)part.dynamicPressurekPa; // comparing as float since this is computed from floats
	Vector3 stock_dragVectorDir = part.dragVectorDir;
	float stock_dragScalar = part.dragScalar;
	Vector3 stock_liftForce = part.DragCubes.LiftForce;
	float stock_liftScalar = part.bodyLiftScalar;
	if (!Numerics.AlmostEqual(stock_rb_angularDrag, kspcf_rb_AngularDrag, 20))
	Debug.Log($"[FIAeroDebug] Mismatching RB angularDrag : {Math.Abs(stock_rb_angularDrag - kspcf_rb_AngularDrag)}");
	if (!Numerics.AlmostEqual(stock_dynamicPressurekPa, kspcf_dynamicPressurekPa, 20))
	Debug.Log($"[FIAeroDebug] Mismatching dynamicPressurekPa : {Math.Abs(stock_dynamicPressurekPa - kspcf_dynamicPressurekPa)}");
	if (stock_dragVectorDir != kspcf_dragVectorDir)
	Debug.Log($"[FIAeroDebug] Mismatching dragVectorDir : {(stock_dragVectorDir - kspcf_dragVectorDir).magnitude}");
	if (!Numerics.AlmostEqual(stock_dragScalar, kspcf_dragScalar, 20))
	Debug.Log($"[FIAeroDebug] Mismatching dragScalar : {Math.Abs(stock_dragScalar - kspcf_dragScalar)}");
	if (stock_liftForce != kspcf_liftForce)
	Debug.Log($"[FIAeroDebug] Mismatching liftForce : {(stock_liftForce - kspcf_liftForce).magnitude}");
	if (!Numerics.AlmostEqual(stock_liftScalar, kspcf_liftScalar, 20))
	Debug.Log($"[FIAeroDebug] Mismatching liftScalar : {Math.Abs(stock_liftScalar - kspcf_liftScalar)}");
	}
	#endif