Added VelIntercept.

- Uses the same code as Thing_ProjectileIntercept to aim and move the projectile.
  - targ: The actor the caller will aim at.
  - speed: Used for calculating the new angle/pitch and adjusts the speed accordingly. Default is -1 (current speed).
  - aimpitch: If true, aims the pitch in the travelling direction. Default is true.
  - oldvel: If true, does not replace the velocity with the specified speed. Default is false.

- Split the code from Thing_ProjectileIntercept and have that function call VelIntercept.

src/p_things.cpp

@@ -171,6 +171,85 @@ bool P_Thing_Move (int tid, AActor *source, int mapspot, bool fog)
 	return false;
 }
 
+// [MC] Was part of P_Thing_Projectile, now its own function for use in ZScript.
+// Aims mobj at targ based on speed and targ's velocity.
+void VelIntercept(AActor *targ, AActor *mobj, double speed, bool aimpitch = false, bool oldvel = false)
+{
+	if (targ == nullptr || mobj == nullptr)	return;
+
+	if (speed > 0 && !targ->Vel.isZero())
+	{
+		DVector3 aim = mobj->Vec3To(targ);
+		aim.Z += targ->Height / 2;
+		// Aiming at the target's position some time in the future
+		// is basically just an application of the law of sines:
+		//     a/sin(A) = b/sin(B)
+		// Thanks to all those on the notgod phorum for helping me
+		// with the math. I don't think I would have thought of using
+		// trig alone had I been left to solve it by myself.
+
+		bool nolead = false;
+		DVector3 tvel = targ->Vel;
+		if (!(targ->flags & MF_NOGRAVITY) && targ->waterlevel < 3)
+		{ // If the target is subject to gravity and not underwater,
+		  // assume that it isn't moving vertically. Thanks to gravity,
+		  // even if we did consider the vertical component of the target's
+		  // velocity, we would still miss more often than not.
+			tvel.Z = 0.0;
+			nolead = !!(targ->Vel.X == 0 && targ->Vel.Y == 0);
+		}
+		if (!nolead)
+		{
+			double dist = aim.Length();
+			double targspeed = tvel.Length();
+			double ydotx = -aim | tvel;
+			double a = g_acos(clamp(ydotx / targspeed / dist, -1.0, 1.0));
+			double multiplier = double(pr_leadtarget.Random2())*0.1 / 255 + 1.1;
+			double sinb = -clamp(targspeed*multiplier * g_sin(a) / speed, -1.0, 1.0);
+			DVector3 prevel = mobj->Vel;
+			// Use the cross product of two of the triangle's sides to get a
+			// rotation vector.
+			DVector3 rv(tvel ^ aim);
+			// The vector must be normalized.
+			rv.MakeUnit();
+			// Now combine the rotation vector with angle b to get a rotation matrix.
+			DMatrix3x3 rm(rv, g_cos(g_asin(sinb)), sinb);
+			// And multiply the original aim vector with the matrix to get a
+			// new aim vector that leads the target.
+			DVector3 aimvec = rm * aim;
+			// And make the projectile follow that vector at the desired speed.
+			mobj->Vel = aimvec * (speed / dist);
+			mobj->AngleFromVel();
+			if (oldvel)
+			{
+				mobj->Vel = prevel;
+			}
+			if (aimpitch) // [MC] Ripped right out of A_FaceMovementDirection
+			{
+				const DVector2 velocity = mobj->Vel.XY();
+				mobj->Angles.Pitch = -VecToAngle(velocity.Length(), mobj->Vel.Z);
+			}
+		}
+		else
+		{
+			mobj->Angles.Yaw = mobj->AngleTo(targ);
+			mobj->Vel = aim.Resized(speed);
+		}
+	}
+}
+
+DEFINE_ACTION_FUNCTION(AActor, VelIntercept)
+{
+	PARAM_SELF_PROLOGUE(AActor);
+	PARAM_OBJECT_NOT_NULL(targ, AActor);
+	PARAM_FLOAT_DEF(speed);
+	PARAM_BOOL_DEF(aimpitch);
+	PARAM_BOOL_DEF(oldvel);
+	if (speed < 0)	speed = self->Speed;
+	VelIntercept(targ, self, speed, aimpitch, oldvel);
+	return 0;
+}
+
 bool P_Thing_Projectile (int tid, AActor *source, int type, const char *type_name, DAngle angle,
 	double speed, double vspeed, int dest, AActor *forcedest, int gravity, int newtid,
 	bool leadTarget)
@@ -252,58 +331,11 @@ bool P_Thing_Projectile (int tid, AActor *source, int type, const char *type_nam
 					}
 					mobj->target = spot;
 
-					if (targ != NULL)
+					if (targ != nullptr)
 					{
-						DVector3 aim = mobj->Vec3To(targ);
+						if (leadTarget)
-						aim.Z += targ->Height / 2;
-
-						if (leadTarget && speed > 0 && !targ->Vel.isZero())
 						{
-							// Aiming at the target's position some time in the future
+							VelIntercept(targ, mobj, speed);
-							// is basically just an application of the law of sines:
-							//     a/sin(A) = b/sin(B)
-							// Thanks to all those on the notgod phorum for helping me
-							// with the math. I don't think I would have thought of using
-							// trig alone had I been left to solve it by myself.
-
-							DVector3 tvel = targ->Vel;
-							if (!(targ->flags & MF_NOGRAVITY) && targ->waterlevel < 3)
-							{ // If the target is subject to gravity and not underwater,
-							  // assume that it isn't moving vertically. Thanks to gravity,
-							  // even if we did consider the vertical component of the target's
-							  // velocity, we would still miss more often than not.
-								tvel.Z = 0.0;
-								if (targ->Vel.X == 0 && targ->Vel.Y == 0)
-								{
-									goto nolead;
-								}
-							}
-							double dist = aim.Length();
-							double targspeed = tvel.Length();
-							double ydotx = -aim | tvel;
-							double a = g_acos (clamp (ydotx / targspeed / dist, -1.0, 1.0));
-							double multiplier = double(pr_leadtarget.Random2())*0.1/255+1.1;
-							double sinb = -clamp (targspeed*multiplier * g_sin(a) / speed, -1.0, 1.0);
-
-							// Use the cross product of two of the triangle's sides to get a
-							// rotation vector.
-							DVector3 rv(tvel ^ aim);
-							// The vector must be normalized.
-							rv.MakeUnit();
-							// Now combine the rotation vector with angle b to get a rotation matrix.
-							DMatrix3x3 rm(rv, g_cos(g_asin(sinb)), sinb);
-							// And multiply the original aim vector with the matrix to get a
-							// new aim vector that leads the target.
-							DVector3 aimvec = rm * aim;
-							// And make the projectile follow that vector at the desired speed.
-							mobj->Vel = aimvec * (speed / dist);
-							mobj->AngleFromVel();
-						}
-						else
-						{
-nolead:
-							mobj->Angles.Yaw = mobj->AngleTo(targ);
-							mobj->Vel = aim.Resized (speed);
 						}
 						if (mobj->flags2 & MF2_SEEKERMISSILE)
 						{

wadsrc/static/zscript/actor.txt

@@ -683,6 +683,7 @@ class Actor : Thinker native
 	native clearscope vector2 Vec2Angle(double length, double angle, bool absolute = false) const;
 	native clearscope vector2 Vec2Offset(double x, double y, bool absolute = false) const;
 	native clearscope vector3 Vec2OffsetZ(double x, double y, double atz, bool absolute = false) const;
+	native void VelIntercept(Actor targ, double speed = -1, bool aimpitch = true, bool oldvel = false);
 	native void VelFromAngle(double speed = 0, double angle = 0);
 	native void Vel3DFromAngle(double speed, double angle, double pitch);
 	native void Thrust(double speed = 0, double angle = 0);