Remove "full" grid loading method

I see no reason to let the choice between a greedy and a lighter loading method, so better remove it to simplify the code.

gridio.lua

@@ -7,42 +7,12 @@ local sbyte, schar = string.byte, string.char
 local unpk = unpack
 
 -- Loading files
-local function load_full_map(filename, bytes, signed, size, converter)
-	local file = io.open(worldpath .. filename, 'rb')
-	local data = file:read('*all')
-	if #data < bytes*size then
-		data = minetest.decompress(data)
-	end
-
-	local map = {}
-
-	for i=1, size do
-		local i0 = (i-1)*bytes+1
-		local elements = {data:byte(i0, i1)}
-		local n = sbyte(data, i0)
-		if signed and n >= 128 then
-			n = n - 256
-		end
-
-		for j=1, bytes-1 do
-			n = n*256 + sbyte(data, i0+j)
-		end
-
-		map[i] = n
-	end
-	file:close()
-
-	if converter then
-		for i=1, size do
-			map[i] = converter(map[i])
-		end
-	end
-
-	return map
-end
 
+-- Never load the full map during mapgen. Instead, create an empty lookup table
+-- and read the file on-the-fly when an element is requested for the first time,
+-- using __index metamethod.
 local loader_mt = {
-	__index = function(loader, i)
+	__index = function(loader, i) -- Called when accessing a missing key
 		local file = loader.file
 		local bytes = loader.bytes
 		file:seek('set', (i-1)*bytes)
@@ -60,12 +30,13 @@ local loader_mt = {
 		if loader.conv then
 			n = loader.conv(n)
 		end
+		-- Cache key for next use
 		loader[i] = n
 		return n
 	end,
 }
 
-local function interactive_loader(filename, bytes, signed, size, converter)
+function mapgen_rivers.load_file(filename, bytes, signed, size, converter)
 	local file = io.open(worldpath .. filename, 'rb')
 	if file then
 		converter = converter or false
@@ -73,24 +44,8 @@ local function interactive_loader(filename, bytes, signed, size, converter)
 	end
 end
 
-local load_methods = {
-	full        = load_full_map,
-	interactive = interactive_loader,
-}
-
-function mapgen_rivers.load_file(...)
-	local load_method = mapgen_rivers.settings.load_method
-	local load_func = load_methods[load_method]
-	if load_func then
-		return load_func(...)
-	else
-		minetest.log("error", ("[mapgen_rivers] Unknown load method %s"):format(load_method))
-	end
-end
-
 -- Writing files
 function mapgen_rivers.write_file(filename, data, bytes)
-	local size = #data
 	local file = io.open(worldpath .. filename, 'wb')
 
 	local bytelist = {}
@@ -98,7 +53,7 @@ function mapgen_rivers.write_file(filename, data, bytes)
 		bytelist[j] = 0
 	end
 
-	for i=1, size do
+	for i=1, #data do
 		local n = floor(data[i])
 		data[i] = n
 		for j=bytes, 2, -1 do

gridmanager.lua

@@ -31,44 +31,12 @@ local grid_maps_list = {
 	offset_y = {bytes=1, signed=true, conv=offset_conv},
 }
 
-local function apply_grid_conversion(grid)
-	if grid.load_method ~= "full" then
-		minetest.log("warning", ("Could not apply data conversion for load method %s"):format(grid.load_method))
-		return false
-	end
-	if grid.conv_applied then
-		return true
-	end
-
-	local size = grid.size.x * grid.size.y
-	for mapname, params in pairs(grid_maps_list) do
-		local conv = params.conv
-		if conv then
-			local map = grid[mapname]
-			for i=1, size do
-				map[i] = conv(map[i])
-			end
-		end
-	end
-	grid.conv_applied = true
-
-	return true
-end
-
 function mapgen_rivers.try_load_grid(grid)
-	local load_method = mapgen_rivers.settings.load_method
-
-	-- First, check whether a grid is already loaded with the appropriate method
-	if mapgen_rivers.grid and mapgen_rivers.grid.load_method == load_method then
-		if not mapgen_rivers.grid.conv_applied then
-			apply_grid_conversion(mapgen_rivers.grid)
-		end
+	-- First, check whether a grid is already loaded
+	if mapgen_rivers.grid then
 		return true
 	-- Then, check the provided argument is a valid grid
-	elseif grid and grid.load_method == load_method then
-		if not mapgen_rivers.grid.conv_applied then
-			apply_grid_conversion(grid)
-		end
+	elseif grid then
 		mapgen_rivers.grid = grid
 		on_grid_loaded_callback(grid)
 		return true
@@ -85,21 +53,15 @@ function mapgen_rivers.try_load_grid(grid)
 		return false
 	end
 
-	if load_method == "full" then
-		minetest.log("action", '[mapgen_rivers] Loading full grid')
-	elseif load_method == "interactive" then
-		minetest.log("action", '[mapgen_rivers] Loading grid as interactive loaders')
-	end
+	minetest.log("action", '[mapgen_rivers] Loading grid')
 
 	grid = {
-		load_method = load_method,
 		size = {x=x, y=z},
 	}
 
 	for map, params in pairs(grid_maps_list) do
 		grid[map] = mapgen_rivers.load_file(map, params.bytes, params.signed, x*z, params.conv)
 	end
-	grid.conv_applied = true
 
 	mapgen_rivers.grid = grid
 	on_grid_loaded_callback(grid)
@@ -115,7 +77,6 @@ function mapgen_rivers.generate_grid()
 	local xsize = math.floor(mapgen_rivers.settings.map_x_size / blocksize)
 	local zsize = math.floor(mapgen_rivers.settings.map_z_size / blocksize)
 	grid.size = {x=xsize, y=zsize}
-	grid.conv_applied = false
 
 	if not mapgen_rivers.pregenerate then
 		minetest.log("error", "[mapgen_rivers] Pre-generation function is not available.")
@@ -130,11 +91,6 @@ end
 function mapgen_rivers.write_grid(grid)
 	minetest.mkdir(world_data)
 
-	if grid.conv_applied then
-		minetest.log("error", '[mapgen_rivers] Could not write grid if data conversion is already done')
-		return false
-	end
-
 	for map, params in pairs(grid_maps_list) do
 		mapgen_rivers.write_file(map, grid[map], params.bytes)
 	end

init.lua

@@ -21,6 +21,6 @@ minetest.register_on_mods_loaded(function()
 
 		local grid = mapgen_rivers.generate_grid()
 		mapgen_rivers.write_grid(grid)
-		mapgen_rivers.try_load_grid(grid) -- Reload if needed
+		mapgen_rivers.try_load_grid() -- Reload if needed
 	end
 end)

pregenerate.lua

@@ -110,7 +110,5 @@ function mapgen_rivers.pregenerate(grid)
 	grid.offset_x = offset_x
 	grid.offset_y = offset_y
 
-	grid.load_method = "full"
-	grid.conv_applied = false
 	collectgarbage()
 end

settings.lua

@@ -109,13 +109,8 @@ mapgen_rivers.settings = {
 	tectonic_speed = def_setting('tectonic_speed', 'number'),
 	evol_time = def_setting('evol_time', 'number'),
 	evol_time_step = def_setting('evol_time_step', 'number'),
-
-	load_all = mtsettings:get_bool('mapgen_rivers_load_all')
 }
 
-mapgen_rivers.settings.load_method =
-		mapgen_rivers.settings.load_all and "full" or "interactive"
-
 mapgen_rivers.noise_params = {
 	base = def_setting("np_base", "noise"),
 	distort_x = def_setting("np_distort_x", "noise"),

settings_default.json

@@ -25,7 +25,6 @@
 	"tectonic_speed": 70,
 	"evol_time": 10,
 	"evol_time_step": 1,
-	"load_all": false,
 
 	"np_base": {
 		"offset": 0,

settingtypes.txt

@@ -70,11 +70,6 @@ mapgen_rivers_glacier_widening_factor (Glacier widening factor) float 8.0 1.0 20
 #    This results in mountains being more covered by snow.
 mapgen_rivers_elevation_chill (Elevation chill) float 0.25 0.0 5.0
 
-#    If enabled, loads all grid data in memory at init time.
-#    If disabled, data will be loaded on request and cached in memory.
-#    It's recommended to disable it for very large maps (> 2000 grid nodes or so)
-mapgen_rivers_load_all (Load all data in memory) bool false
-
 [Landscape evolution parameters]
 
 #    Modelled landscape evolution time, in arbitrary units