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local Pos = require"common.coords".Pos
local class = require"common.class"
local bit = require"bit"
local tau = 2*math.pi
math.randomseed(os.time())
local function hash_list(t)
local h = #t
for _,x in ipairs(t) do
x = bit.bxor(bit.rshift(x,16),x) * 0x7feb352d
x = bit.bxor(bit.rshift(x,15),x) * 0x846ca68b
x = bit.bxor(bit.rshift(x,16),x)
h = bit.bxor(h,x + 0x9e3779b9 + bit.lshift(h,6) + bit.rshift(h,2))
end
return h
end
local function hash_to_unit_vec(t)
local h = hash_list(t)
math.randomseed(h)
local theta = math.random()*tau
return Pos:make(math.cos(theta),math.sin(theta))
end
local function lerp(a,b,t) return (1-t)*a + t*b end
local function smoothstep(x)
if x<0 then return 0 end
if x>1 then return 1 end
return x*x*(3 - 2*x)
end
local function slerp(a,b,t) return lerp(a,b,smoothstep(t)) end
local PerlinNoise = class()
function PerlinNoise.make(cls,seed)
return setmetatable({seed=seed},cls)
end
function PerlinNoise.vertex(self,ix,iy)
return hash_to_unit_vec{ix,iy,self.seed}
end
function PerlinNoise.at(self,x,y)
local x0 = math.floor(x)
local y0 = math.floor(y)
local x1 = x0 + 1
local y1 = y0 + 1
local v00 = self:vertex(x0,y0)
local v01 = self:vertex(x0,y1)
local v10 = self:vertex(x1,y0)
local v11 = self:vertex(x1,y1)
local p = function(...) return Pos:make(...) end
local d00 = v00:dot(p(x-x0,y-y0))
local d01 = v01:dot(p(x-x0,y-y1))
local d10 = v10:dot(p(x-x1,y-y0))
local d11 = v11:dot(p(x-x1,y-y1))
local q0 = slerp(d00,d01,y-y0)
local q1 = slerp(d10,d11,y-y0)
local z = slerp(q0,q1,x-x0)
return z
end
local NoiseAgg = class()
function NoiseAgg.make(cls,things)
return setmetatable({things=things or {}},cls)
end
function NoiseAgg.at(self,x,y)
local n = 0
local t = 0
assert(#self.things>0,"can't generate noise with no noise things")
for _,thing in ipairs(self.things) do
local gen,scale,amp = thing.gen,thing.scale,thing.amp
n = n + amp
t = t + gen:at(x/scale,y/scale)*amp
end
return t/n
end
return {PerlinNoise=PerlinNoise,NoiseAgg=NoiseAgg}
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