[MIRROR] Infrared Emitters use beam datums (As God intended) (#1539)

* Infrared Emitters use beam datums (As God intended)  (#82094)

## About The Pull Request

Fixes #64459 
Fixes #82052  , probably
Fixes #79747 , probably
Fixes #81443 

Infrared emitters now use beam datums instead of making their own
effects and trying to `Move` it out until it hits something

This means 

1. Infrared emitters are (probably) more responsive
2. Infrared emitters (probably) react to less things they shouldn't
react to (such as projectiles)

This also means

- Infrared emitters (when visible) are emissive (and glow in the dark
slightly). Kinda neat? If you don't want it you can obviously just make
it invisible
- You can limbo under beams? Maybe you can do that already? IDK

Other notes

- Beams no longer set their beam component's `x`, `y` directly, now
using `forceMove`


![image](https://github.com/tgstation/tgstation/assets/51863163/1d516703-1f95-4c8e-a83b-89acaf20e5af)


![image](https://github.com/tgstation/tgstation/assets/51863163/ddb8eb51-f787-4def-82bd-8c2b878327f6)


https://github.com/tgstation/tgstation/assets/51863163/29b76b58-ef36-4c4a-a3b2-017b625389dd

## Changelog

:cl: Melbert
refactor: Infrared emitters now function better (or at least more how
you would expect them) (hopefully). Report any oddities
/:cl:

* Infrared Emitters use beam datums (As God intended)

---------

Co-authored-by: MrMelbert <[email protected]>

code/__DEFINES/dcs/signals/signals_beam.dm

@@ -1,3 +1,12 @@
 /// Called before beam is redrawn
 #define COMSIG_BEAM_BEFORE_DRAW "beam_before_draw"
 	#define BEAM_CANCEL_DRAW (1 << 0)
+
+/// Sent to a beam when an atom enters any turf the beam covers: (obj/effect/ebeam/hit_beam, atom/movable/entered)
+#define COMSIG_BEAM_ENTERED "beam_entered"
+
+/// Sent to a beam when an atom exits any turf the beam covers: (obj/effect/ebeam/hit_beam, atom/movable/exited)
+#define COMSIG_BEAM_EXITED "beam_exited"
+
+/// Sent to a beam when any turf the beam covers changes: (list/datum/callback/post_change_callbacks)
+#define COMSIG_BEAM_TURFS_CHANGED "beam_turfs_changed"

code/datums/beam.dm

@@ -163,16 +163,16 @@
 			Pixel_y = round(cos(Angle)+32*cos(Angle)*(N+16)/32)
 
 		//Position the effect so the beam is one continous line
-		var/a
+		var/final_x = segment.x
+		var/final_y = segment.y
 		if(abs(Pixel_x)>32)
-			a = Pixel_x > 0 ? round(Pixel_x/32) : CEILING(Pixel_x/32, 1)
-			segment.x += a
+			final_x += Pixel_x > 0 ? round(Pixel_x/32) : CEILING(Pixel_x/32, 1)
 			Pixel_x %= 32
 		if(abs(Pixel_y)>32)
-			a = Pixel_y > 0 ? round(Pixel_y/32) : CEILING(Pixel_y/32, 1)
-			segment.y += a
+			final_y += Pixel_y > 0 ? round(Pixel_y/32) : CEILING(Pixel_y/32, 1)
 			Pixel_y %= 32
 
+		segment.forceMove(locate(final_x, final_y, segment.z))
 		segment.pixel_x = origin_px + Pixel_x
 		segment.pixel_y = origin_py + Pixel_y
 		CHECK_TICK
@@ -194,6 +194,7 @@
 		return
 	var/mutable_appearance/emissive_overlay = emissive_appearance(icon, icon_state, src)
 	emissive_overlay.transform = transform
+	emissive_overlay.alpha = alpha
 	. += emissive_overlay
 
 /obj/effect/ebeam/Destroy()
@@ -202,9 +203,69 @@
 
 /obj/effect/ebeam/singularity_pull()
 	return
+
 /obj/effect/ebeam/singularity_act()
 	return
 
+/// A beam subtype used for advanced beams, to react to atoms entering the beam
+/obj/effect/ebeam/reacting
+	/// If TRUE, atoms that exist in the beam's loc when inited count as "entering" the beam
+	var/react_on_init = FALSE
+
+/obj/effect/ebeam/reacting/Initialize(mapload, beam_owner)
+	. = ..()
+	var/static/list/loc_connections = list(
+		COMSIG_ATOM_ENTERED = PROC_REF(on_entered),
+		COMSIG_ATOM_EXITED = PROC_REF(on_exited),
+		COMSIG_TURF_CHANGE = PROC_REF(on_turf_change),
+	)
+	AddElement(/datum/element/connect_loc, loc_connections)
+
+	if(!isturf(loc) || isnull(owner) || mapload || !react_on_init)
+		return
+
+	for(var/atom/movable/existing as anything in loc)
+		beam_entered(existing)
+
+/obj/effect/ebeam/reacting/proc/on_entered(datum/source, atom/movable/entered)
+	SIGNAL_HANDLER
+
+	if(isnull(owner))
+		return
+
+	beam_entered(entered)
+
+/obj/effect/ebeam/reacting/proc/on_exited(datum/source, atom/movable/exited)
+	SIGNAL_HANDLER
+
+	if(isnull(owner))
+		return
+
+	beam_exited(exited)
+
+/obj/effect/ebeam/reacting/proc/on_turf_change(datum/source, path, new_baseturfs, flags, list/datum/callback/post_change_callbacks)
+	SIGNAL_HANDLER
+
+	if(isnull(owner))
+		return
+
+	beam_turfs_changed(post_change_callbacks)
+
+/// Some atom entered the beam's line
+/obj/effect/ebeam/reacting/proc/beam_entered(atom/movable/entered)
+	SHOULD_CALL_PARENT(TRUE)
+	SEND_SIGNAL(owner, COMSIG_BEAM_ENTERED, src, entered)
+
+/// Some atom exited the beam's line
+/obj/effect/ebeam/reacting/proc/beam_exited(atom/movable/exited)
+	SHOULD_CALL_PARENT(TRUE)
+	SEND_SIGNAL(owner, COMSIG_BEAM_EXITED, src, exited)
+
+/// Some turf the beam covers has changed to a new turf type
+/obj/effect/ebeam/reacting/proc/beam_turfs_changed(list/datum/callback/post_change_callbacks)
+	SHOULD_CALL_PARENT(TRUE)
+	SEND_SIGNAL(owner, COMSIG_BEAM_TURFS_CHANGED, post_change_callbacks)
+
 /**
  * This is what you use to start a beam. Example: origin.Beam(target, args). **Store the return of this proc if you don't set maxdist or time, you need it to delete the beam.**
  *
@@ -221,5 +282,3 @@
 	var/datum/beam/newbeam = new(src,BeamTarget,icon,icon_state,time,maxdistance,beam_type, beam_color, emissive, override_origin_pixel_x, override_origin_pixel_y, override_target_pixel_x, override_target_pixel_y )
 	INVOKE_ASYNC(newbeam, TYPE_PROC_REF(/datum/beam/, Start))
 	return newbeam
-
-

code/modules/antagonists/heretic/magic/fire_blast.dm

@@ -31,7 +31,7 @@
 
 /datum/action/cooldown/spell/charged/beam/fire_blast/send_beam(atom/origin, mob/living/carbon/to_beam, bounces = 4)
 	// Send a beam from the origin to the hit mob
-	origin.Beam(to_beam, icon_state = "solar_beam", time = beam_duration, beam_type = /obj/effect/ebeam/fire)
+	origin.Beam(to_beam, icon_state = "solar_beam", time = beam_duration, beam_type = /obj/effect/ebeam/reacting/fire)
 
 	// If they block the magic, the chain wont necessarily stop,
 	// but likely will (due to them not catching on fire)
@@ -141,25 +141,11 @@
 	owner.adjustStaminaLoss(2 * tick_damage * seconds_between_ticks)
 
 // The beam fireblast spits out, causes people to walk through it to be on fire
-/obj/effect/ebeam/fire
+/obj/effect/ebeam/reacting/fire
 	name = "fire beam"
 
-/obj/effect/ebeam/fire/Initialize(mapload)
+/obj/effect/ebeam/reacting/fire/beam_entered(atom/movable/entered)
 	. = ..()
-	var/static/list/loc_connections = list(
-		COMSIG_ATOM_ENTERED = PROC_REF(on_entered),
-	)
-	AddElement(/datum/element/connect_loc, loc_connections)
-
-	if(!isturf(loc) || mapload) // idk if this would ever be maploaded but you never know
-		return
-
-	for(var/mob/living/living_mob in loc)
-		on_entered(entered = living_mob)
-
-/obj/effect/ebeam/fire/proc/on_entered(datum/source, atom/movable/entered)
-	SIGNAL_HANDLER
-
 	if(!isliving(entered))
 		return
 	var/mob/living/living_entered = entered