Add backend functionality for metaballs

Implementing a frontend command sounds like a headache to me

worldeditadditions/init.lua

@@ -59,6 +59,7 @@ dofile(wea.modpath.."/lib/scale.lua")
 dofile(wea.modpath.."/lib/spiral_square.lua")
 dofile(wea.modpath.."/lib/spiral_circle.lua")
 dofile(wea.modpath.."/lib/dome.lua")
+dofile(wea.modpath.."/lib/metaballs.lua")
 dofile(wea.modpath.."/lib/conv/conv.lua")
 dofile(wea.modpath.."/lib/erode/erode.lua")
 dofile(wea.modpath.."/lib/noise/init.lua")

worldeditadditions/lib/metaballs.lua

@@ -0,0 +1,63 @@
+local wea = worldeditadditions
+local Vector3 = wea.Vector3
+
+-- ███    ███ ███████ ████████  █████  ██████   █████  ██      ██      ███████
+-- ████  ████ ██         ██    ██   ██ ██   ██ ██   ██ ██      ██      ██
+-- ██ ████ ██ █████      ██    ███████ ██████  ███████ ██      ██      ███████
+-- ██  ██  ██ ██         ██    ██   ██ ██   ██ ██   ██ ██      ██           ██
+-- ██      ██ ███████    ██    ██   ██ ██████  ██   ██ ███████ ███████ ███████
+--- Renders 2 or more metaballs with the given node and threshold value.
+-- direction the point should point.
+-- @param	metaballs		[{pos: Vector3, radius: number}]	Aa list of metaballs to render. Each metaball should be a table with 2 properties: pos - the position of the centre of the metaball as a Vector3, and radius - the radius of the metaball.
+-- @param	replace_node	string		The fully qualified name of the node to use to make the dome with.
+function worldeditadditions.metaballs(metaballs, replace_node, threshold)
+	local pos1, pos2
+	if not threshold then threshold = 1 end
+	
+	for i,metaball in ipairs(metaballs) do
+		local pos1_c = metaball.pos - metaball.radius
+		local pos2_c = metaball.pos + metaball.radius
+		if i == 1 then
+			pos1 = pos1_c
+			pos2 = pos2_c
+		end
+		pos1 = Vector3.min(pos1, pos1_c)
+		pos2 = Vector3.max(pos2, pos2_c)
+	end
+	
+	-- pos2 will always have the highest co-ordinates now
+	
+	-- Fetch the nodes in the specified area
+	local manip, area = worldedit.manip_helpers.init(pos1, pos2)
+	local data = manip:get_data()
+	
+	local node_id_replace = minetest.get_content_id(replace_node)
+	
+	
+	local replaced = 0
+	for z = pos2.z, pos1.z, -1 do
+		for y = pos2.y, pos1.y, -1 do
+			for x = pos2.x, pos1.x, -1 do
+				local pos_here = Vector3.new(x, y, z)
+				
+				local metaball_sum = 0
+				for i,metaball in ipairs(metaballs) do
+					local distance_sq = (metaball.pos - pos_here):length_squared()
+					local radius_sq = metaball.radius * metaball.radius
+					local falloff = (1 / (distance_sq/radius_sq)) ^ 2
+					metaball_sum = metaball_sum + falloff
+				end
+				
+				if metaball_sum <= threshold then
+					data[area:index(x, y, z)] = node_id_replace
+					replaced = replaced + 1
+				end
+			end
+		end
+	end
+	
+	-- Save the modified nodes back to disk & return
+	worldedit.manip_helpers.finish(manip, data)
+	
+	return true, replaced
+end