Add feature to customize how CMs are launched (scp-fs2open#7224)

Author: MjnMixael

code/cmeasure/cmeasure.cpp

@@ -25,36 +25,50 @@ const float CMEASURE_DETONATE_DISTANCE = 40.0f;
 
 //Used to set a countermeasure velocity after being launched from a ship as a countermeasure
 //ie not as a primary or secondary.
-void cmeasure_set_ship_launch_vel(object *objp, object *parent_objp, int arand)
+void cmeasure_set_ship_launch_vel(object* objp, object* parent_objp, int arand)
 {
-	vec3d vel, rand_vec;
+	vec3d vel;
+	vec3d rand_vec;
+	vec3d world_dir;
 
-	//Get cmeasure rear velocity in world
-	vm_vec_scale_add(&vel, &parent_objp->phys_info.vel, &parent_objp->orient.vec.fvec, -25.0f);
+	weapon* wp = &Weapons[objp->instance];
+	auto* wip = &Weapon_info[wp->weapon_info_index];
+
+	// Start with parent velocity
+	vel = parent_objp->phys_info.vel;
+
+	// Normalize direction
+	vec3d local_dir = wip->cm_launch_vec;
+	if (vm_vec_mag_squared(&local_dir) > 0.0f) {
+		vm_vec_normalize(&local_dir);
+	}
 
-	//Get random velocity vector
-	static_randvec(arand+1, &rand_vec);
+	// Convert from ship to world space
+	vm_vec_unrotate(&world_dir, &local_dir, &parent_objp->orient);
 
-	//Add it to the rear velocity
-	vm_vec_scale_add2(&vel, &rand_vec, 2.0f);
+	// Apply launch impulse
+	vm_vec_scale_add2(&vel, &world_dir, wip->cm_launch_speed);
+
+	// Add random variance
+	static_randvec(arand + 1, &rand_vec);
+	vm_vec_scale_add2(&vel, &rand_vec, wip->cm_launch_variance);
 
 	objp->phys_info.vel = vel;
 
 	//Zero out this stuff so it isn't moving
 	vm_vec_zero(&objp->phys_info.rotvel);
 	vm_vec_zero(&objp->phys_info.max_vel);
 	vm_vec_zero(&objp->phys_info.max_rotvel);
-	
+
 	// blow out his reverse thrusters. Or drag, same thing.
 	objp->phys_info.rotdamp = 10000.0f;
 	objp->phys_info.side_slip_time_const = 10000.0f;
 
-	objp->phys_info.max_vel.xyz.z = -25.0f;
-	vm_vec_copy_scale(&objp->phys_info.desired_vel, &objp->orient.vec.fvec, objp->phys_info.max_vel.xyz.z );
+	// Desired velocity should align with launch direction, not hardcoded backward
+	vm_vec_copy_scale(&objp->phys_info.desired_vel, &world_dir, wip->cm_launch_speed);
 
 	// if this cmeasure has a single segment trail, let the trail know since we just changed the velocity
 	// yeah this is hacky but that's what this function gets for CHANGING the velocity on objects with a ""CONSTANT VELOCITY""
-	weapon* wp = &Weapons[objp->instance];
 	if (wp->trail_ptr && wp->trail_ptr->single_segment) {
 		wp->trail_ptr->vel[0] = objp->phys_info.vel;
 		wp->trail_ptr->vel[1] = objp->phys_info.vel;

code/weapon/weapon.h

@@ -627,6 +627,9 @@ struct weapon_info
 	float cm_heat_effectiveness;
 	float cm_effective_rad;
 	float cm_detonation_rad;
+	vec3d cm_launch_vec;
+	float cm_launch_speed;
+	float cm_launch_variance;
 	bool  cm_kill_single;       // should the countermeasure kill just the single decoyed missile within CMEASURE_DETONATE_DISTANCE?
 	int   cmeasure_timer_interval;	// how many milliseconds between pulses
 	int cmeasure_firewait;						// delay in milliseconds between countermeasure firing --wookieejedi

code/weapon/weapons.cpp

@@ -2842,6 +2842,26 @@ int parse_weapon(int subtype, bool replace, const char *filename)
 		if (optional_string("+Missile Detonation Radius:"))
 			stuff_float(&wip->cm_detonation_rad);
 
+		if (optional_string("+Launch Vector:")) {
+			stuff_vec3d(&wip->cm_launch_vec);
+		}
+
+		if (optional_string("+Launch Speed:")) {
+			stuff_float(&wip->cm_launch_speed);
+			if (wip->cm_launch_speed < 0) {
+				Warning(LOCATION, "Countermeasure launch speed for weapon \'%s\' should be non-negative. Value will not be used.", wip->name);
+				wip->cm_launch_speed = 25.0f;
+			}
+		}
+
+		if (optional_string("+Launch Variance:")) {
+			stuff_float(&wip->cm_launch_variance);
+			if (wip->cm_launch_variance < 0) {
+				Warning(LOCATION, "Countermeasure launch variance for weapon \'%s\' should be non-negative. Value will not be used.", wip->name);
+				wip->cm_launch_variance = 2.0f;
+			}
+		}
+
 		if (optional_string("+Single Missile Kill:"))
 			stuff_boolean(&wip->cm_kill_single);
 
@@ -9684,6 +9704,9 @@ void weapon_info::reset()
 	this->cm_heat_effectiveness = 1.0f;
 	this->cm_effective_rad = MAX_CMEASURE_TRACK_DIST;
 	this->cm_detonation_rad = CMEASURE_DETONATE_DISTANCE;
+	this->cm_launch_vec = {{{0.0f, 0.0f, -1.0f}}};
+	this->cm_launch_speed = 25.0f;
+	this->cm_launch_variance = 2.0f;
 	this->cm_kill_single = false;
 	this->cmeasure_timer_interval = 0;
 	this->cmeasure_firewait = CMEASURE_WAIT;