//===========================================================================
   //
   // AlignToPlane
   // Original code written by ZZYZX
   //
   //===========================================================================

	static void AlignToPlane(Actor a = null, double pitchAdjust = 0, bool ceiling = false, double adjustSpeed = 1.0)
	{
		if (!a) return;
		double ceilingAdjust = 0;
		Vector3 fnormal;
		if (!ceiling)
		{
		 fnormal = a.CurSector.FloorPlane.Normal;
		}
		else
		{
		 fnormal = a.CurSector.CeilingPlane.Normal;
		 ceilingAdjust = 180.0;
		}
		Vector2 fnormalp1 = (fnormal.x != 0 || fnormal.y != 0) ? (fnormal.x, fnormal.y).Unit() : (0, 0);
		Vector2 fnormalp2 = ((fnormal.x, fnormal.y).Length(), fnormal.z);
		double dang = a.Angle;
		double fang = atan2(fnormalp1.y, fnormalp1.x);
		double fpitch = atan2(fnormalp2.x, fnormalp2.y);
		double ddiff1 = sin(fang - (dang - pitchAdjust));
		double ddiff2 = cos(fang - dang);

		double pitchTarget = (fpitch * ddiff2 - pitchAdjust) + ceilingAdjust;
		double rollTarget = -fpitch * ddiff1 + ceilingAdjust;
		double angleTarget = dang + ceilingAdjust;

		if(a.Pitch < pitchTarget)
		{
			a.Pitch += adjustSpeed;
			if(a.Pitch > pitchTarget)
			{
				a.Pitch = pitchTarget;
			}
		}
		else if(a.Pitch > pitchTarget)
		{
			a.Pitch -= adjustSpeed;
			if(a.Pitch < pitchTarget)
			{
				a.Pitch = pitchTarget;
			}
		}
		if(a.Roll < rollTarget)
		{
			a.Roll += adjustSpeed;
			if(a.Roll > rollTarget)
			{
				a.Roll = rollTarget;
			}
		}
		else if(a.Roll > rollTarget)
		{
			a.Roll -= adjustSpeed;
			if(a.Roll < rollTarget)
			{
				a.Roll = rollTarget;
			}
		}
		if(a.Angle < angleTarget)
		{
			a.Angle += adjustSpeed;
			if(a.Angle > angleTarget)
			{
				a.Angle = angleTarget;
			}
		}
		else if(a.Angle > angleTarget)
		{
			a.Angle -= adjustSpeed;
			if(a.Angle < angleTarget)
			{
				a.Angle = angleTarget;
			}
		}
	}