Fixes observe issues with parallax (#25561)

This fixes #25479 plus a runtime that happens when you observe a mob whose player has ghosted that results in a comically incorrect HUD for the observer.

HUDs are a fucking mess still to the surprise of nobody

code/_onclick/hud/hud.dm

@@ -141,10 +141,9 @@
 /datum/hud/proc/show_hud(version = 0,mob/viewmob)
 	if(!ismob(mymob))
 		return 0
-	if(!mymob.client)
-		return 0
-
 	var/mob/screenmob = viewmob || mymob
+	if(!screenmob.client)
+		return 0
 
 	screenmob.client.screen = list()
 
@@ -166,7 +165,7 @@
 			if(infodisplay.len)
 				screenmob.client.screen += infodisplay
 
-			mymob.client.screen += hide_actions_toggle
+			screenmob.client.screen += hide_actions_toggle
 
 			if(action_intent)
 				action_intent.screen_loc = initial(action_intent.screen_loc) //Restore intent selection to the original position
@@ -210,7 +209,7 @@
 	mymob.update_action_buttons(1)
 	reorganize_alerts()
 	mymob.reload_fullscreen()
-	create_parallax()
+	update_parallax_pref(screenmob)
 
 
 /datum/hud/human/show_hud(version = 0,mob/viewmob)

code/_onclick/hud/parallax.dm

@@ -11,9 +11,10 @@
 	var/parallax_layers_max = 3
 	var/parallax_animate_timer
 
-/datum/hud/proc/create_parallax()
-	var/client/C = mymob.client
-	if (!apply_parallax_pref())
+/datum/hud/proc/create_parallax(mob/viewmob)
+	var/mob/screenmob = viewmob || mymob
+	var/client/C = screenmob.client
+	if (!apply_parallax_pref(viewmob)) //don't want shit computers to crash when specing someone with insane parallax, so use the viewer's pref
 		return
 
 	if(!length(C.parallax_layers_cached))
@@ -27,7 +28,10 @@
 		C.parallax_layers.len = C.parallax_layers_max
 
 	C.screen |= (C.parallax_layers)
-	var/obj/screen/plane_master/PM = plane_masters["[PLANE_SPACE]"]
+	var/obj/screen/plane_master/PM = screenmob.hud_used.plane_masters["[PLANE_SPACE]"]
+	if(screenmob != mymob)
+		C.screen -= locate(/obj/screen/plane_master/parallax_white) in C.screen
+		C.screen += PM
 	PM.color = list(
 		0, 0, 0, 0,
 		0, 0, 0, 0,
@@ -37,15 +41,20 @@
 		)
 
 
-/datum/hud/proc/remove_parallax()
-	var/client/C = mymob.client
+/datum/hud/proc/remove_parallax(mob/viewmob)
+	var/mob/screenmob = viewmob || mymob
+	var/client/C = screenmob.client
 	C.screen -= (C.parallax_layers_cached)
-	var/obj/screen/plane_master/PM = plane_masters["[PLANE_SPACE]"]
+	var/obj/screen/plane_master/PM = screenmob.hud_used.plane_masters["[PLANE_SPACE]"]
+	if(screenmob != mymob)
+		C.screen -= locate(/obj/screen/plane_master/parallax_white) in C.screen
+		C.screen += PM
 	PM.color = initial(PM.color)
 	C.parallax_layers = null
 
-/datum/hud/proc/apply_parallax_pref()
-	var/client/C = mymob.client
+/datum/hud/proc/apply_parallax_pref(mob/viewmob)
+	var/mob/screenmob = viewmob || mymob
+	var/client/C = screenmob.client
 	if(C.prefs)
 		var/pref = C.prefs.parallax
 		if (isnull(pref))
@@ -75,9 +84,9 @@
 	C.parallax_layers_max = 3
 	return TRUE
 
-/datum/hud/proc/update_parallax_pref()
-	remove_parallax()
-	create_parallax()
+/datum/hud/proc/update_parallax_pref(mob/viewmob)
+	remove_parallax(viewmob)
+	create_parallax(viewmob)
 
 // This sets which way the current shuttle is moving (returns true if the shuttle has stopped moving so the caller can append their animation)
 /datum/hud/proc/set_parallax_movedir(new_parallax_movedir, skip_windups)

code/modules/client/preferences.dm

@@ -1210,12 +1210,12 @@ var/list/preferences_datums = list()
 				if("parallaxup")
 					parallax = Wrap(parallax + 1, PARALLAX_INSANE, PARALLAX_DISABLE + 1)
 					if (parent && parent.mob && parent.mob.hud_used)
-						parent.mob.hud_used.update_parallax_pref()
+						parent.mob.hud_used.update_parallax_pref(parent.mob)
 
 				if("parallaxdown")
 					parallax = Wrap(parallax - 1, PARALLAX_INSANE, PARALLAX_DISABLE + 1)
 					if (parent && parent.mob && parent.mob.hud_used)
-						parent.mob.hud_used.update_parallax_pref()
+						parent.mob.hud_used.update_parallax_pref(parent.mob)
 
 				if("save")
 					save_preferences()

code/modules/mob/dead/observer/observer.dm

@@ -805,7 +805,7 @@ This is the proc mobs get to turn into a ghost. Forked from ghostize due to comp
 		if(mob_eye.hud_used)
 			LAZYINITLIST(mob_eye.observers)
 			mob_eye.observers |= src
-			mob_eye.hud_used.show_hud(1,src)
+			mob_eye.hud_used.show_hud(mob_eye.hud_used.hud_version, src)
 			observetarget = mob_eye
 
 /mob/dead/observer/verb/register_pai_candidate()