Implements fuel fires

Implements liquid fuel fires using the liquid fuel cleanable decal objects.
Rewrites zburn to be more sane, replaces convoluted calculations with straightforward reaction limit.
Fixes issue with liquid fuel spreading caused by thee object being deleted.
Prevents zones from being repeatedly added to the active fire zones list, and processed repeatedly.

code/ZAS/Fire.dm

@@ -20,7 +20,7 @@ atom/proc/temperature_expose(datum/gas_mixture/air, exposed_temperature, exposed
 turf/proc/hotspot_expose(exposed_temperature, exposed_volume, soh = 0)
 
 
-turf/simulated/hotspot_expose(exposed_temperature, exposed_volume, soh)
+/turf/simulated/hotspot_expose(exposed_temperature, exposed_volume, soh)
 	if(fire_protection > world.time-300)
 		return 0
 	if(locate(/obj/fire) in src)
@@ -35,37 +35,35 @@ turf/simulated/hotspot_expose(exposed_temperature, exposed_volume, soh)
 	if(air_contents.check_combustability(liquid))
 		igniting = 1
 
-		create_fire(1000)
+		create_fire(vsc.fire_firelevel_multiplier)
 	return igniting
 
 /zone/proc/process_fire()
-	if(!air.check_combustability())
+	var/datum/gas_mixture/burn_gas = air.remove_ratio(vsc.fire_consuption_rate, fire_tiles.len)
+
+	var/firelevel = burn_gas.zburn(src, fire_tiles, force_burn = 1, no_check = 1)
+	//world << "[src]: firelevel [firelevel]"
+
+	air.merge(burn_gas)
+
+	if(firelevel)
+		for(var/turf/T in fire_tiles)
+			if(T.fire)
+				T.fire.firelevel = firelevel
+			else
+				var/obj/effect/decal/cleanable/liquid_fuel/fuel = locate() in T
+				fire_tiles -= T
+				fuel_objs -= fuel
+	else
 		for(var/turf/simulated/T in fire_tiles)
 			if(istype(T.fire))
 				T.fire.RemoveFire()
 			T.fire = null
 		fire_tiles.Cut()
+		fuel_objs.Cut()
 
 	if(!fire_tiles.len)
 		air_master.active_fire_zones.Remove(src)
-		return
-
-	var/datum/gas_mixture/burn_gas = air.remove_ratio(vsc.fire_consuption_rate, fire_tiles.len)
-	var/gm = burn_gas.group_multiplier
-
-	burn_gas.group_multiplier = 1
-	burn_gas.zburn(force_burn = 1, no_check = 1)
-	burn_gas.group_multiplier = gm
-
-	air.merge(burn_gas)
-
-	var/firelevel = air.calculate_firelevel()
-
-	for(var/turf/T in fire_tiles)
-		if(T.fire)
-			T.fire.firelevel = firelevel
-		else
-			fire_tiles -= T
 
 /turf/proc/create_fire(fl)
 	return 0
@@ -79,8 +77,12 @@ turf/simulated/hotspot_expose(exposed_temperature, exposed_volume, soh)
 		return 1
 
 	fire = new(src, fl)
-	zone.fire_tiles |= src
 	air_master.active_fire_zones |= zone
+	
+	var/obj/effect/decal/cleanable/liquid_fuel/fuel = locate() in src
+	zone.fire_tiles |= src
+	if(fuel) zone.fuel_objs += fuel
+	
 	return 0
 
 /obj/fire
@@ -121,8 +123,8 @@ turf/simulated/hotspot_expose(exposed_temperature, exposed_volume, soh)
 		SetLuminosity(3)
 
 	//im not sure how to implement a version that works for every creature so for now monkeys are firesafe
-	for(var/mob/living/carbon/human/M in loc)
-		M.FireBurn(firelevel, air_contents.temperature, air_contents.return_pressure())  //Burn the humans!
+	for(var/mob/living/L in loc)
+		L.FireBurn(firelevel, air_contents.temperature, air_contents.return_pressure())  //Burn the mobs!
 
 	loc.fire_act(air_contents, air_contents.temperature, air_contents.volume)
 	for(var/atom/A in loc)
@@ -137,10 +139,11 @@ turf/simulated/hotspot_expose(exposed_temperature, exposed_volume, soh)
 				if(!enemy_tile.zone || enemy_tile.fire)
 					continue
 
-				if(!enemy_tile.zone.fire_tiles.len)
-					var/datum/gas_mixture/acs = enemy_tile.return_air()
-					if(!acs || !acs.check_combustability())
-						continue
+				//if(!enemy_tile.zone.fire_tiles.len) TODO - optimize
+				var/datum/gas_mixture/acs = enemy_tile.return_air()
+				var/obj/effect/decal/cleanable/liquid_fuel/liquid = locate() in enemy_tile
+				if(!acs || !acs.check_combustability(liquid))
+					continue
 
 				//If extinguisher mist passed over the turf it's trying to spread to, don't spread and
 				//reduce firelevel.
@@ -169,85 +172,117 @@ turf/simulated/hotspot_expose(exposed_temperature, exposed_volume, soh)
 
 /obj/fire/Del()
 	if (istype(loc, /turf/simulated))
-		SetLuminosity(0)
-
-		loc = null
-	air_master.active_hotspots.Remove(src)
+		RemoveFire()
 
 	..()
 
 /obj/fire/proc/RemoveFire()
 	if (istype(loc, /turf))
 		SetLuminosity(0)
+		
 		loc = null
 	air_master.active_hotspots.Remove(src)
 
 
-turf/simulated/var/fire_protection = 0 //Protects newly extinguished tiles from being overrun again.
-turf/proc/apply_fire_protection()
-turf/simulated/apply_fire_protection()
+/turf/simulated/var/fire_protection = 0 //Protects newly extinguished tiles from being overrun again.
+/turf/proc/apply_fire_protection()
+/turf/simulated/apply_fire_protection()
 	fire_protection = world.time
 
-
-datum/gas_mixture/proc/zburn(obj/effect/decal/cleanable/liquid_fuel/liquid, force_burn, no_check = 0)
+//Returns the firelevel
+/datum/gas_mixture/proc/zburn(zone/zone, force_burn, no_check = 0)
 	. = 0
-	if((temperature > PHORON_MINIMUM_BURN_TEMPERATURE || force_burn) && (no_check ||check_recombustability(liquid)))
+	if((temperature > PHORON_MINIMUM_BURN_TEMPERATURE || force_burn) && (no_check ||check_recombustability(zone? zone.fuel_objs : null)))
+		var/gas_fuel = 0 //in the case of mixed gas/liquid fires, the gas burns first.
+		var/liquid_fuel = 0
 		var/total_fuel = 0
 		var/total_oxidizers = 0
 
+		//*** Get the fuel and oxidizer amounts
 		for(var/g in gas)
 			if(gas_data.flags[g] & XGM_GAS_FUEL)
-				total_fuel += gas[g]
+				gas_fuel += gas[g]
 			if(gas_data.flags[g] & XGM_GAS_OXIDIZER)
 				total_oxidizers += gas[g]
+		gas_fuel *= group_multiplier
+		total_oxidizers *= group_multiplier
 
-		if(liquid)
 		//Liquid Fuel
-			if(liquid.amount <= 0.1)
-				del liquid
-			else
-				total_fuel += liquid.amount
+		if(zone)
+			for(var/obj/effect/decal/cleanable/liquid_fuel/fuel in zone.fuel_objs)
+				liquid_fuel += fuel.amount*LIQUIDFUEL_AMOUNT_TO_MOL
 
-		if(total_fuel == 0)
+		total_fuel = gas_fuel + liquid_fuel
+		if(total_fuel <= 0.005)
 			return 0
 
-		//Calculate the firelevel.
-		var/firelevel = calculate_firelevel(liquid, total_fuel, total_oxidizers, force = 1)
+		//*** Determine how fast the fire burns
 
-		//get the current inner energy of the gas mix
+		//calculate the firelevel.
+		var/firelevel = calculate_firelevel(zone? zone.fuel_objs : null, total_fuel, total_oxidizers, force = 1)
+
+		//get the current thermal energy of the gas mix
 		//this must be taken here to prevent the addition or deletion of energy by a changing heat capacity
 		var/starting_energy = temperature * heat_capacity()
 
-		//determine the amount of oxygen used
-		var/used_oxidizers = min(total_oxidizers, total_fuel / 2)
+		//determine how far the reaction can progress
+		var/reaction_limit = min(total_oxidizers*(FIRE_REACTION_FUEL_AMOUNT/FIRE_REACTION_OXIDIZER_AMOUNT), total_fuel) //stoichiometric limit
 		
-		//determine the amount of fuel actually used
-		var/used_fuel_ratio = min(2 * total_oxidizers , total_fuel) / total_fuel
-		total_fuel = total_fuel * used_fuel_ratio
+		//determine the actual rate of reaction, as measured by the amount of fuel reacting
 		
-		var/total_reactants = total_fuel + used_oxidizers
+		//vapour fuels are extremely volatile! The reaction progress is a percentage of the total fuel (similar to old zburn).
+		var/gas_reaction_progress = max(0.2*group_multiplier, (firelevel/vsc.fire_firelevel_multiplier)*gas_fuel)*FIRE_GAS_BURNRATE_MULT
+		//liquid fuels are not as volatile, and the reaction progress depends on the size of the area that is burning (which is sort of accounted for by firelevel). Having more fuel means a longer burn.
+		var/liquid_reaction_progress = (firelevel/vsc.fire_firelevel_multiplier)*FIRE_LIQUID_BURNRATE_MULT
 		
-		//determine the amount of reactants actually reacting
-		var/used_reactants_ratio = min(max(total_reactants * firelevel / vsc.fire_firelevel_multiplier, 0.2), total_reactants) / total_reactants
+		//world << "liquid_reaction_progress = [liquid_reaction_progress]"
+		//world << "gas_reaction_progress = [gas_reaction_progress]"
+		
+		var/total_reaction_progress = gas_reaction_progress + liquid_reaction_progress
+		if(total_reaction_progress <= 0)
+			return 0
+		
+		var/used_fuel = min(total_reaction_progress, reaction_limit)
+		var/used_oxidizers = used_fuel*(FIRE_REACTION_OXIDIZER_AMOUNT/FIRE_REACTION_FUEL_AMOUNT)
+		//world << "used_fuel = [used_fuel]; used_oxidizers = [used_oxidizers]; reaction_limit=[reaction_limit]"
+		
+		//*** Remove fuel and oxidizer, add carbon dioxide and heat
 		
 		//remove and add gasses as calculated
-		remove_by_flag(XGM_GAS_OXIDIZER, used_oxidizers * used_reactants_ratio)
-		remove_by_flag(XGM_GAS_FUEL, total_fuel * used_reactants_ratio)
+		var/used_gas_fuel = min(used_fuel*(gas_reaction_progress/total_reaction_progress), gas_fuel) //remove in proportion to the relative reaction progress
+		var/used_liquid_fuel = between(0, used_fuel-used_gas_fuel, liquid_fuel)
 		
-		adjust_gas("carbon_dioxide", max(total_fuel*used_reactants_ratio, 0))
+		//remove_by_flag() and adjust_gas() handle the group_multiplier for us.
+		remove_by_flag(XGM_GAS_OXIDIZER, used_oxidizers)
+		remove_by_flag(XGM_GAS_FUEL, used_gas_fuel)
+		adjust_gas("carbon_dioxide", used_oxidizers)
 
-		if(liquid)
-			liquid.amount -= (liquid.amount * used_fuel_ratio * used_reactants_ratio) * 5 // liquid fuel burns 5 times as quick
+		//As a simplification, we remove fuel equally from all fuel sources. It might be that some fuel sources have more fuel, some have less, but whatever.
+		if(zone && zone.fuel_objs.len)
+			var/fuel_to_remove = used_liquid_fuel/(zone.fuel_objs.len*LIQUIDFUEL_AMOUNT_TO_MOL) //convert back to liquid volume units
+			//world << "used gas fuel = [used_gas_fuel]; used other fuel = [used_fuel-used_gas_fuel]; fuel_to_remove = [fuel_to_remove]"
+			var/liquidonly = !check_combustability()
+			for(var/O in zone.fuel_objs)
+				var/obj/effect/decal/cleanable/liquid_fuel/fuel = O
+				if(!istype(fuel))
+					zone.fuel_objs -= fuel
+					continue
 				
-			if(liquid.amount <= 0) del liquid
+				fuel.amount -= fuel_to_remove
+				if(fuel.amount <= 0)
+					zone.fuel_objs -= fuel
+					if(liquidonly)
+						var/turf/T = fuel.loc
+						if(istype(T) && T.fire) del(T.fire)
+					del(fuel)
 
 		//calculate the energy produced by the reaction and then set the new temperature of the mix
-		temperature = (starting_energy + vsc.fire_fuel_energy_release * total_fuel) / heat_capacity()
+		temperature = (starting_energy + vsc.fire_fuel_energy_release * used_fuel) / heat_capacity()
 
 		update_values()
-		. = total_reactants * used_reactants_ratio
+		return firelevel
 
-datum/gas_mixture/proc/check_recombustability(obj/effect/decal/cleanable/liquid_fuel/liquid)
+datum/gas_mixture/proc/check_recombustability(list/fuel_objs)
 	. = 0
 	for(var/g in gas)
 		if(gas_data.flags[g] & XGM_GAS_OXIDIZER && gas[g] >= 0.1)
@@ -257,7 +292,7 @@ datum/gas_mixture/proc/check_recombustability(obj/effect/decal/cleanable/liquid_
 	if(!.)
 		return 0
 
-	if(liquid)
+	if(fuel_objs && fuel_objs.len)
 		return 1
 
 	. = 0
@@ -266,7 +301,7 @@ datum/gas_mixture/proc/check_recombustability(obj/effect/decal/cleanable/liquid_
 			. = 1
 			break
 
-datum/gas_mixture/proc/check_combustability(obj/effect/decal/cleanable/liquid_fuel/liquid)
+/datum/gas_mixture/proc/check_combustability(obj/effect/decal/cleanable/liquid_fuel/liquid=null)
 	. = 0
 	for(var/g in gas)
 		if(gas_data.flags[g] & XGM_GAS_OXIDIZER && QUANTIZE(gas[g] * vsc.fire_consuption_rate) >= 0.1)
@@ -285,20 +320,12 @@ datum/gas_mixture/proc/check_combustability(obj/effect/decal/cleanable/liquid_fu
 			. = 1
 			break
 
-datum/gas_mixture/proc/calculate_firelevel(obj/effect/decal/cleanable/liquid_fuel/liquid, total_fuel = null, total_oxidizers = null, force = 0)
+//Returns a value between 0 and vsc.fire_firelevel_multiplier
+/datum/gas_mixture/proc/calculate_firelevel(list/fuel_objs, total_fuel, total_oxidizers, force = 0)
 	//Calculates the firelevel based on one equation instead of having to do this multiple times in different areas.
 	var/firelevel = 0
 
-	if(force || check_recombustability(liquid))
-		if(isnull(total_fuel))
-			for(var/g in gas)
-				if(gas_data.flags[g] & XGM_GAS_FUEL)
-					total_fuel += gas[g]
-				if(gas_data.flags[g] & XGM_GAS_OXIDIZER)
-					total_oxidizers += gas[g]
-			if(liquid)
-				total_fuel += liquid.amount
-
+	if(force || check_recombustability(fuel_objs))
 		var/total_combustables = (total_fuel + total_oxidizers)
 
 		if(total_combustables > 0)

code/ZAS/Zone.dm

@@ -44,6 +44,7 @@ Class Procs:
 /zone/var/invalid = 0
 /zone/var/list/contents = list()
 /zone/var/list/fire_tiles = list()
+/zone/var/list/fuel_objs = list()
 
 /zone/var/needs_update = 0
 
@@ -72,8 +73,10 @@ Class Procs:
 	T.zone = src
 	contents.Add(T)
 	if(T.fire)
+		var/obj/effect/decal/cleanable/liquid_fuel/fuel = locate() in T
 		fire_tiles.Add(T)
-		air_master.active_fire_zones.Add(src)
+		air_master.active_fire_zones |= src
+		if(fuel) fuel_objs += fuel
 	T.update_graphic(air.graphic)
 
 /zone/proc/remove(turf/simulated/T)
@@ -85,6 +88,9 @@ Class Procs:
 #endif
 	contents.Remove(T)
 	fire_tiles.Remove(T)
+	if(T.fire)
+		var/obj/effect/decal/cleanable/liquid_fuel/fuel = locate() in T
+		fuel_objs -= fuel
 	T.zone = null
 	T.update_graphic(graphic_remove = air.graphic)
 	if(contents.len)

code/ZAS/_gas_mixture_xgm.dm

@@ -301,7 +301,7 @@
 
 
 /datum/gas_mixture/proc/react(atom/dump_location)
-	zburn(null)
+	zburn(null, force_burn=0, no_check=0) //could probably just call zburn() here with no args but I like being explicit.
 
 
 //Rechecks the gas_mixture and adjusts the graphic list if needed.

code/game/machinery/atmoalter/canister.dm

@@ -199,9 +199,7 @@ update_flag
 	else
 		can_label = 0
 
-	if(air_contents.temperature > PHORON_FLASHPOINT)
-		air_contents.zburn()
-	return
+	air_contents.react() //cooking up air cans - add phoron and oxygen, then heat above PHORON_MINIMUM_BURN_TEMPERATURE
 
 /obj/machinery/portable_atmospherics/canister/return_air()
 	return air_contents

code/game/objects/effects/decals/Cleanable/fuel.dm

@@ -1,10 +1,10 @@
-obj/effect/decal/cleanable/liquid_fuel
+/obj/effect/decal/cleanable/liquid_fuel
 	//Liquid fuel is used for things that used to rely on volatile fuels or phoron being contained to a couple tiles.
 	icon = 'icons/effects/effects.dmi'
 	icon_state = "fuel"
 	layer = TURF_LAYER+0.2
 	anchored = 1
-	var/amount = 1 //Basically moles.
+	var/amount = 1
 
 	New(turf/newLoc,amt=1,nologs=0)
 		if(!nologs)
@@ -16,25 +16,34 @@ obj/effect/decal/cleanable/liquid_fuel
 		for(var/obj/effect/decal/cleanable/liquid_fuel/other in newLoc)
 			if(other != src)
 				other.amount += src.amount
+				
+				var/oldsrc = src
+				src = null
 				spawn other.Spread()
-				del src
+				del(oldsrc)
 
 		Spread()
 		. = ..()
 
-	proc/Spread()
+	proc/Spread(exclude=list())
 		//Allows liquid fuels to sometimes flow into other tiles.
-		if(amount < 5.0) return
+		if(amount < 15) return //lets suppose welder fuel is fairly thick and sticky. For something like water, 5 or less would be more appropriate.
 		var/turf/simulated/S = loc
 		if(!istype(S)) return
 		for(var/d in cardinal)
-			if(rand(25))
-				var/turf/simulated/target = get_step(src,d)
-				var/turf/simulated/origin = get_turf(src)
-				if(origin.CanPass(null, target, 0, 0) && target.CanPass(null, origin, 0, 0))
-					if(!locate(/obj/effect/decal/cleanable/liquid_fuel) in target)
-						new/obj/effect/decal/cleanable/liquid_fuel(target, amount*0.25,1)
-						amount *= 0.75
+			var/turf/simulated/target = get_step(src,d)
+			var/turf/simulated/origin = get_turf(src)
+			if(origin.CanPass(null, target, 0, 0) && target.CanPass(null, origin, 0, 0))
+				var/obj/effect/decal/cleanable/liquid_fuel/other_fuel = locate() in target
+				if(other_fuel)
+					other_fuel.amount += amount*0.25
+					if(!(other_fuel in exclude))
+						exclude += src
+						other_fuel.Spread(exclude)
+				else
+					new/obj/effect/decal/cleanable/liquid_fuel(target, amount*0.25,1)
+				amount *= 0.75
+						
 
 	flamethrower_fuel
 		icon_state = "mustard"

code/game/objects/items/weapons/tanks/tanks.dm

@@ -246,7 +246,7 @@
 
 /obj/item/weapon/tank/process()
 	//Allow for reactions
-	air_contents.react()
+	air_contents.react() //cooking up air tanks - add phoron and oxygen, then heat above PHORON_MINIMUM_BURN_TEMPERATURE
 	check_status()
 
 

code/setup.dm

@@ -122,12 +122,19 @@
 #define CARBON_LIFEFORM_FIRE_DAMAGE     4
 
 // Phoron fire properties.
-#define PHORON_MINIMUM_BURN_TEMPERATURE    (T0C +  100)
-#define PHORON_FLASHPOINT                  (T0C +  246)
-#define PHORON_UPPER_TEMPERATURE           (T0C + 1370)
-#define PHORON_MINIMUM_OXYGEN_NEEDED       2
-#define PHORON_MINIMUM_OXYGEN_PHORON_RATIO 20
-#define PHORON_OXYGEN_FULLBURN             10
+#define PHORON_MINIMUM_BURN_TEMPERATURE    (T0C +  126) //400 K - autoignite temperature in tanks and canisters - enclosed environments I guess
+#define PHORON_FLASHPOINT                  (T0C +  246) //519 K - autoignite temperature in air if that ever gets implemented.
+
+//These control the mole ratio of oxidizer and fuel used in the combustion reaction
+#define FIRE_REACTION_OXIDIZER_AMOUNT	3
+#define FIRE_REACTION_FUEL_AMOUNT		2
+
+//These control the speed at which fire burns
+#define FIRE_GAS_BURNRATE_MULT			1
+#define FIRE_LIQUID_BURNRATE_MULT		0.5
+
+//How many moles of fuel are contained within one solid/liquid fuel volume unit
+#define LIQUIDFUEL_AMOUNT_TO_MOL		1  //mol/volume unit
 
 #define T0C  273.15 //    0.0 degrees celcius
 #define T20C 293.15 //   20.0 degrees celcius