Added margin with a settable width near grid border

Elevation gets closer to -50 when approaching the border

pregenerate.lua

@@ -14,6 +14,38 @@ local time_step = mapgen_rivers.settings.evol_time_step
 local niter = math.ceil(time/time_step)
 time_step = time / niter
 
+local use_margin = true
+local margin_width = 2000 / blocksize
+local margin_elev = -200
+
+local function margin(dem, width, elev)
+	local X, Y = dem.X, dem.Y
+	for i=1, width do
+		local c1 = ((i-1)/width) ^ 0.5
+		local c2 = (1-c1) * elev
+		local index = (i-1)*X + 1
+		for x=1, X do
+			dem[index] = dem[index] * c1 + c2
+			index = index + 1
+		end
+		index = i
+		for y=1, Y do
+			dem[index] = dem[index] * c1 + c2
+			index = index + X
+		end
+		index = X*(Y-i) + 1
+		for x=1, X do
+			dem[index] = dem[index] * c1 + c2
+			index = index + 1
+		end
+		index = X-i + 1
+		for y=1, Y do
+			dem[index] = dem[index] * c1 + c2
+			index = index + X
+		end
+	end
+end
+
 local function pregenerate(keep_loaded)
 	local grid = mapgen_rivers.grid
 	local size = grid.size
@@ -31,6 +63,10 @@ local function pregenerate(keep_loaded)
 	dem.X = size.x
 	dem.Y = size.y
 
+	if use_margin then
+		margin(dem, margin_width, margin_elev)
+	end
+
 	local model = EvolutionModel(evol_params)
 	model.dem = dem
 	local ref_dem = model:define_isostasy(dem)
@@ -46,6 +82,9 @@ local function pregenerate(keep_loaded)
 		if i < niter then
 			if tectonic_step ~= 0 then
 				nobj_base:get_3d_map_flat({x=0, y=tectonic_step*i, z=0}, ref_dem)
+				if use_margin then
+					margin(ref_dem, margin_width, margin_elev)
+				end
 			end
 			model:isostasy()
 		end