Minetest-WorldEditAdditions/worldeditadditions/lib/erode/snowballs.lua

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local wea = worldeditadditions
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local wea_c = worldeditadditions_core
local Vector3 = wea_c.Vector3
-- Test command: //multi //fp set1 1313 6 5540 //fp set2 1338 17 5521 //erode snowballs
local function snowball(heightmap, normalmap, heightmap_size, startpos, params)
local sediment = 0
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local pos = Vector3.new(startpos.x, 0, startpos.z) -- X/Z
local pos_prev = Vector3.new(pos.x, 0, pos.z) -- X/Z
local velocity = Vector3.new(
(math.random() * 2 - 1) * params.init_velocity,
0,
(math.random() * 2 - 1) * params.init_velocity
) -- X/Z
local heightmap_length = #heightmap
-- print("[snowball] startpos ("..pos.x..", "..pos.z.."), velocity: ("..velocity.x..", "..velocity.z..")")
local hist_velocity = {}
for i = 1, params.max_steps do
local x = pos.x
local z = pos.z
local hi = math.floor(z+0.5)*heightmap_size.x + math.floor(x+0.5)
-- Stop if we go out of bounds
if x < 0 or z < 0
or x >= heightmap_size.x-1 or z >= heightmap_size.z-1 then
-- print("[snowball] hit edge; stopping at ("..x..", "..z.."), (bounds @ "..(heightmap_size.x-1)..", "..(heightmap_size.z-1)..")", "x", x, "/", heightmap_size.x-1, "z", z, "/", heightmap_size.z-1)
return true, i
end
if #hist_velocity > 0 and i > 5
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and wea_c.average(hist_velocity) < 0.03 then
-- print("[snowball] It looks like we've stopped")
return true, i
end
if normalmap[hi].y == 1 then return true, i end
if hi > heightmap_length then return false, "Out-of-bounds on the array, hi: "..hi..", heightmap_length: "..heightmap_length end
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-- NOTE: We need to decide whether we want to keep the precomputed normals as we have now, or whether we want to dynamically compute them at the time of request.
-- print("[snowball] sediment", sediment, "rate_deposit", params.rate_deposit, "normalmap[hi].z", normalmap[hi].z)
local step_deposit = sediment * params.rate_deposit * normalmap[hi].z
local step_erode = params.rate_erosion * (1 - normalmap[hi].z) * math.min(1, i*params.scale_iterations)
-- Erode / Deposit, but only if we are on a different node than we were in the last step
if math.floor(pos_prev.x) ~= math.floor(x)
and math.floor(pos_prev.z) ~= math.floor(z) then
heightmap[hi] = heightmap[hi] + (step_deposit - step_erode)
end
velocity.x = params.friction * velocity.x + normalmap[hi].x * params.speed
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velocity.y = 0 -- Just in case
velocity.z = params.friction * velocity.z + normalmap[hi].y * params.speed
-- print("[snowball] now at ("..x..", "..z..") velocity "..velocity:length_squared()..", sediment "..sediment)
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local new_vel_sq = velocity:length_squared()
if new_vel_sq > 1 then
-- print("[snowball] velocity squared over 1, normalising")
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velocity = velocity:normalise()
end
table.insert(hist_velocity, new_vel_sq)
if #hist_velocity > params.velocity_hist_count then table.remove(hist_velocity, 1) end
pos_prev.x = x
pos_prev.z = z
pos.x = pos.x + velocity.x
pos.z = pos.z + velocity.z
sediment = sediment + (step_erode - step_deposit) -- Needs to be erosion - deposit, which is the opposite to the above
end
return true, params.max_steps
end
--[[
2D erosion algorithm based on snowballs
Note that this *mutates* the given heightmap.
@source https://jobtalle.com/simulating_hydraulic_erosion.html
]]--
function wea.erode.snowballs(heightmap_initial, heightmap, heightmap_size, region_height, params_custom)
local params = {
rate_deposit = 0.03, -- 0.03
rate_erosion = 0.04, -- 0.04
friction = 0.07,
speed = 1,
max_steps = 80,
velocity_hist_count = 3,
init_velocity = 0.25,
scale_iterations = 0.04,
maxdiff = 0.4,
count = 25000
}
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-- Apply the custom settings
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wea_c.table.apply(params_custom, params)
-- print("[erode/snowballs] params: ")
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-- print(wea_c.format.map(params))
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local normals = wea_c.terrain.calculate_normals(heightmap, heightmap_size)
local stats_steps = {}
for i = 1, params.count do
-- print("[snowballs] starting snowball ", i)
local success, steps = snowball(
heightmap, normals, heightmap_size,
{
x = math.random() * (heightmap_size.x - 1),
z = math.random() * (heightmap_size.z - 1)
},
params
)
table.insert(stats_steps, steps)
if not success then return false, "Error: Failed at snowball "..i..":"..steps end
end
-- print("[snowballs] "..#stats_steps.." snowballs simulated, max "..params.max_steps.." steps, averaged ~"..wea.average(stats_steps).."")
-- Round everything to the nearest int, since you can't really have
-- something like .141592671 of a node
-- Note that we do this after *all* the erosion is complete
local clamp_limit = math.floor(region_height * params.maxdiff + 0.5)
for i,v in ipairs(heightmap) do
heightmap[i] = math.floor(heightmap[i] + 0.5)
if heightmap[i] < 0 then heightmap[i] = 0 end
-- Limit the distance to params.maxdiff% of the region height
if math.abs(heightmap_initial[i] - heightmap[i]) > region_height * params.maxdiff then
if heightmap_initial[i] - heightmap[i] > 0 then
heightmap[i] = heightmap_initial[i] - clamp_limit
else
heightmap[i] = heightmap_initial[i] + clamp_limit
end
end
end
if not params.noconv then
local success, matrix = wea.get_conv_kernel("gaussian", 3, 3)
if not success then return success, matrix end
local matrix_size = Vector3.new(3, 0, 3)
wea.conv.convolve(
heightmap, heightmap_size,
matrix,
matrix_size
)
end
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return true, ""..#stats_steps.." snowballs simulated, max "..params.max_steps.." steps (averaged ~"..wea_c.average(stats_steps).." steps)"
end