Inverse square law for radiation damage

diff --git a/technic/machines/HV/nuclear_reactor.lua b/technic/machines/HV/nuclear_reactor.lua
index b240a9ddbdaec2a57d7ce652e2a9be7545f2a6fc..7244a0f115a93d862246d6a936422ab9ff67921c 100644 (file)
--- a/technic/machines/HV/nuclear_reactor.lua
+++ b/technic/machines/HV/nuclear_reactor.lua
@@ -12,6 +12,15 @@ local fuel_type    = "technic:uranium_fuel" -- The reactor burns this stuff
 
 local S = technic.getter
 
+if not vector.distance_square then
+       vector.distance_square = function (u, v)
+               local dx = v.x - u.x
+               local dy = v.y - u.y
+               local dz = v.z - u.z
+               return dx*dx + dy*dy + dz*dz
+       end
+end
+
 -- FIXME: recipe must make more sense like a rod recepticle, steam chamber, HV generator?
 minetest.register_craft({
        output = 'technic:hv_nuclear_reactor_core',
@@ -211,7 +220,7 @@ minetest.register_node("technic:hv_nuclear_reactor_core_active", {
        tiles = {"technic_hv_nuclear_reactor_core.png", "technic_hv_nuclear_reactor_core.png",
                 "technic_hv_nuclear_reactor_core.png", "technic_hv_nuclear_reactor_core.png",
                 "technic_hv_nuclear_reactor_core.png", "technic_hv_nuclear_reactor_core.png"},
-       groups = {snappy=2, choppy=2, oddly_breakable_by_hand=2, technic_machine=1, radioactive=2, not_in_creative_inventory=1},
+       groups = {snappy=2, choppy=2, oddly_breakable_by_hand=2, technic_machine=1, radioactive=3, not_in_creative_inventory=1},
        legacy_facedir_simple = true,
        sounds = default.node_sound_wood_defaults(),
        drop="technic:hv_nuclear_reactor_core",
@@ -257,15 +266,46 @@ technic.register_machine("HV", "technic:hv_nuclear_reactor_core_active", technic
 
 -- radioactive materials that can result from destroying a reactor
 
+local assumed_abdomen_offset = vector.new(0, 1, 0)
+local assumed_abdomen_offset_length = vector.length(assumed_abdomen_offset)
+
 minetest.register_abm({
        nodenames = {"group:radioactive"},
        interval = 1,
        chance = 1,
        action = function (pos, node)
-               for r = 1, minetest.registered_nodes[node.name].groups.radioactive do
-                       for _, o in ipairs(minetest.get_objects_inside_radius(pos, r*2)) do
-                               if o:is_player() then
-                                       o:set_hp(math.max(o:get_hp() - 1, 0))
+               -- Damage depends on distance between the radiation source
+               -- and the player, with an inverse square relationship.
+               -- The "radioactive" group value is the distance in
+               -- metres from a node at which a player will be damaged by
+               -- 1 HP/s.  Or, equivalently, it is the square root of the
+               -- damage rate in HP/s that a player 1 m away will take.
+               local strength = minetest.registered_nodes[node.name].groups.radioactive
+               -- Damage is processed at rates down to 0.25 HP/s,
+               -- which is attained at twice the 1 HP/s distance.
+               for _, o in ipairs(minetest.get_objects_inside_radius(pos, strength*2 + assumed_abdomen_offset_length)) do
+                       if o:is_player() then
+                               -- If the player is very close, swimming
+                               -- in radioactive liquid, then the nominal
+                               -- distance could go to zero, but in
+                               -- that case we model the player's body
+                               -- displacing the liquid and increasing
+                               -- the effective distance to non-zero.
+                               -- The minimum effective distance is set
+                               -- to the maximum distance one can get
+                               -- from the node centre within the node,
+                               -- so that swimming in radioactive liquid
+                               -- gives a uniform effective distance.
+                               local dist_sq = math.max(0.75, vector.distance_square(pos, vector.add(o:getpos(), assumed_abdomen_offset)))
+                               local dmg_rate = strength*strength/dist_sq
+                               if dmg_rate >= 0.25 then
+                                       local dmg_int = math.floor(dmg_rate)
+                                       if math.random() < dmg_rate-dmg_int then
+                                               dmg_int = dmg_int + 1
+                                       end
+                                       if dmg_int > 0 then
+                                               o:set_hp(math.max(o:get_hp() - dmg_int, 0))
+                                       end
                                end
                        end
                end
@@ -305,7 +345,7 @@ for _, state in ipairs({ "flowing", "source" }) do
                        liquid = 2,
                        hot = 3,
                        igniter = 1,
-                       radioactive = (state == "source" and 3 or 2),
+                       radioactive = (state == "source" and 4 or 3),
                        not_in_creative_inventory = (state == "flowing" and 1 or nil),
                },
        })
@@ -325,7 +365,7 @@ minetest.register_node("technic:chernobylite_block", {
         description = S("Chernobylite Block"),
        tiles = { "technic_chernobylite_block.png" },
        is_ground_content = true,
-       groups = { cracky=1, radioactive=1, level=2 },
+       groups = { cracky=1, radioactive=2, level=2 },
        sounds = default.node_sound_stone_defaults(),
        light_source = 2,