mapgen_rivers/polygons.lua

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local X = mapgen_rivers.grid.size.x
local Z = mapgen_rivers.grid.size.y
local function index(x, z)
return z*X+x+1
end
local settings = mapgen_rivers.settings
local blocksize = tonumber(settings:get('blocksize'))
local min_catchment = tonumber(settings:get('min_catchment'))
local map_offset = {x=0, z=0}
if settings:get_bool('center') then
map_offset.x = blocksize*X/2
map_offset.z = blocksize*Z/2
end
-- Localize for performance
local floor, ceil, min, max, abs = math.floor, math.ceil, math.min, math.max, math.abs
min_catchment = min_catchment / (blocksize*blocksize)
local wpower = settings:get('river_widening_power')
local wfactor = 1/(2*blocksize * min_catchment^wpower)
local function river_width(flow)
flow = abs(flow)
if flow < min_catchment then
return 0
end
return min(wfactor * flow ^ wpower, 1)
end
local noise_heat -- Need a large-scale noise here so no heat blend
local elevation_chill = settings:get_bool('elevation_chill')
local function get_temperature(x, y, z)
local pos = {x=x, y=z}
return noise_heat:get2d(pos) - y*elevation_chill
end
local glaciers = settings:get_bool('glaciers')
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local glacier_factor = tonumber(settings:get('glacier_factor'))
local init = false
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-- On map generation, determine into which polygon every point (in 2D) will fall.
-- Also store polygon-specific data
local function make_polygons(minp, maxp)
local grid = mapgen_rivers.grid
local dem = grid.dem
local lakes = grid.lakes
local dirs = grid.dirs
local rivers = grid.rivers
local offset_x = grid.offset_x
local offset_z = grid.offset_y
if not init then
if glaciers then
noise_heat = minetest.get_perlin(mapgen_rivers.noise_params.heat)
end
init = true
end
local chulens = maxp.x - minp.x + 1
local polygons = {}
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-- Determine the minimum and maximum coordinates of the polygons that could be on the chunk, knowing that they have an average size of 'blocksize' and a maximal offset of 0.5 blocksize.
local xpmin, xpmax = max(floor((minp.x+map_offset.x)/blocksize - 0.5), 0), min(ceil((maxp.x+map_offset.x)/blocksize + 0.5), X-2)
local zpmin, zpmax = max(floor((minp.z+map_offset.z)/blocksize - 0.5), 0), min(ceil((maxp.z+map_offset.z)/blocksize + 0.5), Z-2)
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-- Iterate over the polygons
for xp = xpmin, xpmax do
for zp=zpmin, zpmax do
local iA = index(xp, zp)
local iB = index(xp+1, zp)
local iC = index(xp+1, zp+1)
local iD = index(xp, zp+1)
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-- Extract the vertices of the polygon
local poly_x = {
(offset_x[iA]+xp) * blocksize - map_offset.x,
(offset_x[iB]+xp+1) * blocksize - map_offset.x,
(offset_x[iC]+xp+1) * blocksize - map_offset.x,
(offset_x[iD]+xp) * blocksize - map_offset.x,
}
local poly_z = {
(offset_z[iA]+zp) * blocksize - map_offset.z,
(offset_z[iB]+zp) * blocksize - map_offset.z,
(offset_z[iC]+zp+1) * blocksize - map_offset.z,
(offset_z[iD]+zp+1) * blocksize - map_offset.z,
}
local polygon = {x=poly_x, z=poly_z, i={iA, iB, iC, iD}}
local bounds = {} -- Will be a list of the intercepts of polygon edges for every Z position (scanline algorithm)
-- Calculate the min and max Z positions
local zmin = max(floor(min(unpack(poly_z)))+1, minp.z)
local zmax = min(floor(max(unpack(poly_z))), maxp.z)
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-- And initialize the arrays
for z=zmin, zmax do
bounds[z] = {}
end
local i1 = 4
for i2=1, 4 do -- Loop on 4 edges
local z1, z2 = poly_z[i1], poly_z[i2]
-- Calculate the integer Z positions over which this edge spans
local lzmin = floor(min(z1, z2))+1
local lzmax = floor(max(z1, z2))
if lzmin <= lzmax then -- If there is at least one position in it
local x1, x2 = poly_x[i1], poly_x[i2]
-- Calculate coefficient of the equation defining the edge: X=aZ+b
local a = (x1-x2) / (z1-z2)
local b = (x1 - a*z1)
for z=max(lzmin, minp.z), min(lzmax, maxp.z) do
-- For every Z position involved, add the intercepted X position in the table
table.insert(bounds[z], a*z+b)
end
end
i1 = i2
end
for z=zmin, zmax do
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-- Now sort the bounds list
local zlist = bounds[z]
table.sort(zlist)
local c = floor(#zlist/2)
for l=1, c do
-- Take pairs of X coordinates: all positions between them belong to the polygon.
local xmin = max(floor(zlist[l*2-1])+1, minp.x)
local xmax = min(floor(zlist[l*2]), maxp.x)
local i = (z-minp.z) * chulens + (xmin-minp.x) + 1
for x=xmin, xmax do
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-- Fill the map at these places
polygons[i] = polygon
i = i + 1
end
end
end
local poly_dem = {dem[iA], dem[iB], dem[iC], dem[iD]}
polygon.dem = poly_dem
polygon.lake = {lakes[iA], lakes[iB], lakes[iC], lakes[iD]}
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-- Now, rivers.
-- Load river flux values for the 4 corners
local riverA = river_width(rivers[iA])
local riverB = river_width(rivers[iB])
local riverC = river_width(rivers[iC])
local riverD = river_width(rivers[iD])
if glaciers then -- Widen the river
if get_temperature(poly_x[1], poly_dem[1], poly_z[1]) < 0 then
riverA = min(riverA*glacier_factor, 1)
end
if get_temperature(poly_x[2], poly_dem[2], poly_z[2]) < 0 then
riverB = min(riverB*glacier_factor, 1)
end
if get_temperature(poly_x[3], poly_dem[3], poly_z[3]) < 0 then
riverC = min(riverC*glacier_factor, 1)
end
if get_temperature(poly_x[4], poly_dem[4], poly_z[4]) < 0 then
riverD = min(riverD*glacier_factor, 1)
end
end
polygon.river_corners = {riverA, 1-riverB, 2-riverC, 1-riverD}
-- Flow directions
local dirA, dirB, dirC, dirD = dirs[iA], dirs[iB], dirs[iC], dirs[iD]
-- Determine the river flux on the edges, by testing dirs values
local river_west = (dirA==1 and riverA or 0) + (dirD==3 and riverD or 0)
local river_north = (dirA==2 and riverA or 0) + (dirB==4 and riverB or 0)
local river_east = 1 - (dirB==1 and riverB or 0) - (dirC==3 and riverC or 0)
local river_south = 1 - (dirD==2 and riverD or 0) - (dirC==4 and riverC or 0)
polygon.rivers = {river_west, river_north, river_east, river_south}
end
end
return polygons
end
return make_polygons