Mount Gen: cone can be used as truncated cone. Closes #1893

mods/lord/World/mountgen/algorithms/cone.lua

@@ -1,7 +1,11 @@
-local math_max, math_sqrt, math_floor
-    = math.max, math.sqrt, math.floor
+local math_min, math_max, math_floor, math_ceil, math_sqrt, math_tan, math_rad
+    = math.min, math.max, math.floor, math.ceil, math.sqrt, math.tan, math.rad
 
 
+local MIN_CONE_FOOT_DIAMETER = 3
+
+--- @param diameter number
+--- @return number[][]
 local function fill_with_zeroes(diameter)
 	local map = {}
 	for i = 1, diameter do
@@ -12,27 +16,38 @@ local function fill_with_zeroes(diameter)
 	return map
 end
 
----Generate mountain as cone
----@param diameter number desired width of the mountain
----@param height   number mountain height
----@return table, number, number "height map, map size, center_coordinate"
-mountgen.cone = function(diameter, height)
-	diameter = math_max(diameter, 1)
-	height   = math_max(height, 1)
+--- Generate mountain as cone
+--- @param top_pos Position
+--- @param config  table
+--- @return table, number, number "height map, map size, center_coordinate"
+mountgen.cone = function(top_pos, config)
+	local H = top_pos.y - config.Y0                        -- height of truncated cone
+	local W = 2 * (config.TOP_RADIUS + math_ceil(          -- width (diameter) of cone foot
+		H * math_tan( math_rad(90 - config.ANGLE) )
+	))
+
+	local diameter = math_max(W, MIN_CONE_FOOT_DIAMETER)
+	local radius   = diameter / 2
+	local height   = math_ceil( radius * math_tan( math_rad(config.ANGLE) ) )  -- height of full cone (not truncated)
 
-	local height_map = fill_with_zeroes(diameter)
+	local height_map_size   = math_min(W, 2 * config.MAX_RADIUS)
+	local height_map_radius = math_floor(height_map_size / 2)
+	local height_map        = fill_with_zeroes(height_map_size)
 
-	local radius = diameter / 2
-	local l0     = math_sqrt(radius^2 + radius^2)
+	local l0 = math_sqrt(radius^2 + radius^2)
+
+	for z = 0, height_map_size - 1 do
+		for x = 0, height_map_size - 1 do
+			local px = x - height_map_radius
+			local pz = z - height_map_radius
 
-	for z = 0, diameter - 1 do
-		for x = 0, diameter - 1 do
-			local px = x - radius
-			local pz = z - radius
 			local l  = math_sqrt(px^2 + pz^2)
-			local h  = height * (1 - 2 * l / l0)
-			mountgen.set_value(height_map, z, x, h)
+			if l <= height_map_radius then
+				local h  = height * (1 - 2 * l / l0)
+				mountgen.set_value(height_map, z, x, math_min(h, H))
+			end
 		end
 	end
-	return height_map, diameter, math_floor(radius) + 1
+
+	return height_map, height_map_size, height_map_radius
 end

mods/lord/World/mountgen/mountgen.lua

@@ -60,26 +60,27 @@ mountgen.mountgen = function(top, config)
 		return
 	end
 
-	local y1 = config.Y0
-	local y2 = top.y
-	local H = y2 - y1
-	local W = math_ceil(2 * H * math_tan(config.ANGLE * 3.141 / 180 / 2)) + 3
-
 	local height_map, width, center
 	if method_name == "cone" then
-		height_map, width, center = mountgen.cone(W, H)
+
+		height_map, width, center = mountgen.cone(top, config)
+
 	elseif method_name == "diamond-square" then
+
+		local H = top.y - config.Y0
+		local W = math_ceil(2 * H * math_tan(math.rad(90 - config.ANGLE))) + 3
 		height_map, width, center = mountgen.diamond_square(W, H,
 			config.rk_thr,
 			config.rk_small,
 			config.rk_big)
+
 	else
 		minetest.log("error", "unknown method: " .. tostring(method_name))
 		return
 	end
 
-	local p1 = { x = top.x + 1 - center, y = y1, z = top.z + 1 - center }
-	local p2 = { x = top.x + width - center, y = y2 + 16, z = top.z + width - center }
+	local p1 = { x = top.x + 1 - center, y = config.Y0, z = top.z + 1 - center }
+	local p2 = { x = top.x + width - center, y = top.y + 16, z = top.z + width - center }
 
 	local chunks = mountgen.list_chunks(p1, p2)
 	local voxel_manip = minetest.get_voxel_manip(p1, p2)

mods/lord/World/mountgen/ui.lua

@@ -4,9 +4,14 @@ local esc = minetest.formspec_escape
 mountgen = {
 	required_priv = "server",
 	config = {
-		ANGLE = 120,
+		-- for cone:
+		TOP_RADIUS = 10,
+		MAX_RADIUS = 20,
+		-- /for cone
+
+		ANGLE = 60,
 		Y0 = 0,
-		METHOD = "diamond-square",
+		METHOD = "cone",
 		SNOW_LINE = 50,
 		SNOW_LINE_RAND = 4,
 		GRASS_PERCENT = 10,
@@ -91,7 +96,7 @@ local function validate_config(config)
 			return false
 		end
 	end
-	if config.ANGLE >= 180 then
+	if config.ANGLE < 15 or config.ANGLE > 90 then
 		return false
 	end
 	return true