Changed the way river width is determined in settings

- min_catchment now in square nodes instead of cells
- River widening power as input instead of calculating it from max_catchment

polygons.lua

@@ -90,11 +90,9 @@ if mapgen_rivers.settings.center then
 	map_offset.z = blocksize*Z/2
 end
 
--- Width coefficients: coefficients solving
---   wfactor * min_catchment ^ wpower = 1/(2*blocksize)
---   wfactor * max_catchment ^ wpower = 1
-local wpower = math.log(2*blocksize)/math.log(max_catchment/min_catchment)
-local wfactor = 1 / max_catchment ^ wpower
+local min_catchment = mapgen_rivers.settings.min_catchment / (blocksize*blocksize)
+local wpower = mapgen_rivers.settings.river_widening_power
+local wfactor = 1/(2*blocksize * min_catchment^wpower)
 local function river_width(flow)
 	flow = math.abs(flow)
 	if flow < min_catchment then

settings.lua

@@ -44,8 +44,8 @@ mapgen_rivers.settings = {
 	center = def_setting('center', 'bool', true),
 	blocksize = def_setting('blocksize', 'number', 15),
 	sea_level = tonumber(minetest.get_mapgen_setting('water_level')),
-	min_catchment = def_setting('min_catchment', 'number', 25),
-	max_catchment = def_setting('max_catchment', 'number', 40000),
+	min_catchment = def_setting('min_catchment', 'number', 3600),
+	river_widening_power = def_setting('river_widening_power', 'number', 0.5),
 	riverbed_slope = def_setting('riverbed_slope', 'number', 0.4),
 	distort = def_setting('distort', 'bool', true),
 	biomes = def_setting('biomes', 'bool', true),

settingtypes.txt

@@ -9,15 +9,15 @@ mapgen_rivers_center (Center map) bool true
 #    the actual size of the map will be 12000.
 mapgen_rivers_blocksize (Block size) float 15.0 2.0 100.0
 
-#    Minimal catchment area for a river to be drawn, in grid cells
-#    (1 cell = blocksize x blocksize).
+#    Minimal catchment area for a river to be drawn, in square nodes
 #    Lower value means bigger river density
-mapgen_rivers_min_catchment (Minimal catchment area) float 25.0 1.0 1000.0
+mapgen_rivers_min_catchment (Minimal catchment area) float 3600.0 100.0 1000000.0
 
-#    Catchment area in grid cells (1 grid cell = blocksize x blocksize)
-#    at which rivers reach their maximal width of 2*blocksize.
+#    Coefficient describing how rivers widen when merging.
+#    Riwer width is a power law W = a*D^p. D is river flow and p is this parameter.
 #    Higher value means a river needs to receive more tributaries to grow in width.
-mapgen_rivers_max_catchment (Maximal catchment area) float 40000.0 1000.0 10000000.0
+#    Note that a river can never exceed 2*blocksize.
+mapgen_rivers_river_widening_power (River widening power) float 0.5 0.0 1.0
 
 #    Lateral slope of the riverbed.
 #    Higher value means deeper rivers.