Rebalance radiation shielding

Squeeze the range of material shielding values.  The strongest shielding
materials get weaker, and weaker shielding materials, especially low-end
ones such as dirt, get stronger.  The radioactivity of the active
reactor core is increased so that the standard shielding is (still)
only narrowly sufficient.

diff --git a/technic/machines/HV/nuclear_reactor.lua b/technic/machines/HV/nuclear_reactor.lua
index 19a3c99208456a6e40755652e3f9e2e2341a8477..31252a749571e2045afa72d18880dc9745ce98cb 100644 (file)
--- a/technic/machines/HV/nuclear_reactor.lua
+++ b/technic/machines/HV/nuclear_reactor.lua
@@ -293,7 +293,7 @@ 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 = {cracky=1, technic_machine=1, radioactive=7000, not_in_creative_inventory=1},
+       groups = {cracky=1, technic_machine=1, radioactive=11000, not_in_creative_inventory=1},
        legacy_facedir_simple = true,
        sounds = default.node_sound_wood_defaults(),
        drop="technic:hv_nuclear_reactor_core",
@@ -548,14 +548,18 @@ end
 --
 -- Shielding is assessed by sampling every 0.25 m along the path
 -- from the source to the player, ignoring the source node itself.
--- The summed radiation resistance values from the sampled nodes yield
--- a measure of the total amount of radiation resistance on the path.
--- As in reality, shielding causes exponential attenuation of radiation.
--- However, the effect is scaled down relative to real life: each
--- metre-point of shielding, corresponding to a real-life halving of
--- radiation, reduces radiation by 0.01 nepers (a factor of about 1.01).
--- This scales down the difference between shielded and unshielded safe
--- distances, avoiding the latter becoming impractically large.
+-- The summed shielding values from the sampled nodes yield a measure
+-- of the total amount of shielding on the path.  As in reality,
+-- shielding causes exponential attenuation of radiation.  However, the
+-- effect is scaled down relative to real life.  A metre of a node with
+-- radiation resistance value R yields attenuation of sqrt(R)*0.1 nepers.
+-- (In real life it would be about R*0.69 nepers, by the definition
+-- of the radiation resistance values.)  The sqrt part of this formula
+-- scales down the differences between shielding types, reflecting the
+-- game's simplification of making expensive materials such as gold
+-- readily available in cubic metres.  The multiplicative factor in the
+-- formula scales down the difference between shielded and unshielded
+-- safe distances, avoiding the latter becoming impractically large.
 --
 -- Damage is processed at rates down to 0.25 HP/s, which in the absence of
 -- shielding is attained at the distance specified by the "radioactive"
@@ -565,6 +569,7 @@ end
 -- need to be considered.
 local assumed_abdomen_offset = vector.new(0, 1, 0)
 local assumed_abdomen_offset_length = vector.length(assumed_abdomen_offset)
+local cache_scaled_shielding = {}
 minetest.register_abm({
        nodenames = {"group:radioactive"},
        interval = 1,
@@ -578,15 +583,21 @@ minetest.register_abm({
                                local dist = math.sqrt(dist_sq)
                                local dirstep = dist == 0 and vector.new(0,0,0) or vector.divide(rel, dist*4)
                                local intpos = pos
-                               local resistance = 0
+                               local shielding = 0
                                for intdist = 0.25, dist, 0.25 do
                                        intpos = vector.add(intpos, dirstep)
                                        local intnodepos = vector.round(intpos)
                                        if not vector.equals(intnodepos, pos) then
-                                               resistance = resistance + node_radiation_resistance(minetest.get_node(intnodepos).name)
+                                               local sname = minetest.get_node(intnodepos).name
+                                               local sval = cache_scaled_shielding[sname]
+                                               if not sval then
+                                                       sval = math.sqrt(node_radiation_resistance(sname)) * -0.025
+                                                       cache_scaled_shielding[sname] = sval
+                                               end
+                                               shielding = shielding + sval
                                        end
                                end
-                               local dmg_rate = 0.25e-6 * strength*strength * math.exp(-0.0025*resistance) / math.max(0.75, dist_sq)
+                               local dmg_rate = 0.25e-6 * strength*strength * math.exp(shielding) / math.max(0.75, dist_sq)
                                if dmg_rate >= 0.25 then
                                        local dmg_int = math.floor(dmg_rate)
                                        if math.random() < dmg_rate-dmg_int then