Adds a new element, Self-Knockback. (#47938)

* Adds a new element, Self-Knockback.

* Squashes a potential edgecase runtime in projectile_selfknockback before it can even happen.

* Allows item_selfknockback to interact with dense turfs now.

* Made self-knockback utilize the Element Bespoke flag to allow custom force and speed values on attachment.

* fixes newline issue, adds a usage comment.

* fixes the newline issue in self-knockback for real this time, thanks TortoiseGit.

* i swear on god almighty if this doesn't fix the newline issue, i'll eat a shoe.

* Testing newline lint

code/__DEFINES/components.dm

@@ -306,6 +306,7 @@
 // /obj/projectile signals (sent to the firer)
 #define COMSIG_PROJECTILE_ON_HIT "projectile_on_hit"			// from base of /obj/projectile/proc/on_hit(): (atom/movable/firer, atom/target, Angle)
 #define COMSIG_PROJECTILE_BEFORE_FIRE "projectile_before_fire" 			// from base of /obj/projectile/proc/fire(): (obj/projectile, atom/original_target)
+#define COMSIG_PROJECTILE_FIRE "projectile_fire"				// from the base of /obj/projectile/proc/fire(): ()
 #define COMSIG_PROJECTILE_PREHIT "com_proj_prehit"				// sent to targets during the process_hit proc of projectiles
 
 // /obj/mecha signals

code/datums/elements/selfknockback.dm

@@ -0,0 +1,60 @@
+/datum/element/selfknockback
+	element_flags = ELEMENT_BESPOKE
+	id_arg_index = 2
+	var/override_throw_val
+	var/override_speed_val
+
+/* Adds the ability to put recoil on various things, throwing the user back proportional to the force and speed set.
+Important note: Force/Throw_Amount, is how far you want to throw a user. By default, it is calculated based on damage below.
+Speed_Amount, is a measure of how long it will take a user to get thrown to the target. By default, it is calculated by
+clamping the Knockback_Force value below. */
+/datum/element/selfknockback/Attach(datum/target, throw_amount, speed_amount)
+	. = ..()
+	if(isitem(target))
+		RegisterSignal(target, COMSIG_ITEM_AFTERATTACK, .proc/Item_SelfKnockback)
+	else if(isprojectile(target))
+		RegisterSignal(target, COMSIG_PROJECTILE_FIRE, .proc/Projectile_SelfKnockback)
+	else	
+		return ELEMENT_INCOMPATIBLE
+	
+	override_throw_val = throw_amount
+	override_speed_val = speed_amount
+	
+/datum/element/selfknockback/Detach(datum/source, force)
+	. = ..()
+	UnregisterSignal(source, list(COMSIG_ITEM_AFTERATTACK, COMSIG_PROJECTILE_FIRE))
+
+/datum/element/selfknockback/proc/Get_Knockback_Force(default_force)
+	if(override_throw_val)
+		return override_throw_val
+	else
+		return default_force
+
+/datum/element/selfknockback/proc/Get_Knockback_Speed(default_speed)
+	if(override_speed_val)
+		return override_speed_val
+	else
+		return default_speed
+
+/datum/element/selfknockback/proc/Item_SelfKnockback(obj/item/I, atom/attacktarget, mob/usertarget, proximity_flag)
+	if(isturf(attacktarget) && !attacktarget.density)
+		return
+	if(proximity_flag || (get_dist(attacktarget, usertarget) <= I.reach))
+		var/knockback_force = Get_Knockback_Force(CLAMP(CEILING((I.force / 10), 1), 1, 5))
+		var/knockback_speed = Get_Knockback_Speed(CLAMP(knockback_force, 1, 5))
+
+		var/target_angle = Get_Angle(attacktarget, usertarget)
+		var/move_target = get_ranged_target_turf(usertarget, angle2dir(target_angle), knockback_force)
+		usertarget.throw_at(move_target, knockback_force, knockback_speed)
+		usertarget.visible_message("<span class='warning'>[usertarget] gets thrown back by the force of \the [I] impacting \the [attacktarget]!</span>", "<span class='warning'>The force of \the [I] impacting \the [attacktarget] sends you flying!</span>")
+
+/datum/element/selfknockback/proc/Projectile_SelfKnockback(obj/projectile/P)
+	if(!P.firer)
+		return
+
+	var/knockback_force = Get_Knockback_Force(CLAMP(CEILING((P.damage / 10), 1), 1, 5))
+	var/knockback_speed = Get_Knockback_Speed(CLAMP(knockback_force, 1, 5))
+
+	var/atom/movable/knockback_target = P.firer
+	var/move_target = get_edge_target_turf(knockback_target, angle2dir(P.original_angle+180))
+	knockback_target.throw_at(move_target, knockback_force, knockback_speed)

code/modules/projectiles/projectile.dm

@@ -392,6 +392,7 @@
 	trajectory = new(starting.x, starting.y, starting.z, pixel_x, pixel_y, Angle, SSprojectiles.global_pixel_speed)
 	last_projectile_move = world.time
 	fired = TRUE
+	SEND_SIGNAL(src, COMSIG_PROJECTILE_FIRE)
 	if(hitscan)
 		process_hitscan()
 	if(!(datum_flags & DF_ISPROCESSING))

tgstation.dme

@@ -512,6 +512,7 @@
 #include "code\datums\elements\digitalcamo.dm"
 #include "code\datums\elements\earhealing.dm"
 #include "code\datums\elements\firestacker.dm"
+#include "code\datums\elements\selfknockback.dm"
 #include "code\datums\elements\snail_crawl.dm"
 #include "code\datums\helper_datums\events.dm"
 #include "code\datums\helper_datums\getrev.dm"