Faster watermap (#245)

* created simulation_test.py

* test for _watermap rng stability

* improved comments on test_watermap_rng_stability

* random_land can return a list

* typo in changelog

* test that random_land actually returns land

* missing whitespace

* decided that a recatangle is a better test case than a square w. r. t. indexing correctly.

* more missing whitespaces

* fixed comment to match code

* use faster random land

* random_land returns an array of length num_samples*2

* moved check for no land present outside of loop

* added test for calling watermap with no land

* comments and cleanup

CHANGELOG.md

@@ -1,6 +1,7 @@
 Version 0.20 (UNRELEASED)
 
 * Calculation of sea depth is now faster.
+* Hydrology simulation is now faster.
 
 Version 0.19
 

tests/simulation_test.py

@@ -6,13 +6,7 @@
 from worldengine.model.world import World, Size, GenerationParameters
 
 class TestSimulation(unittest.TestCase):
-
 
-    # The hydrology simulation indirectly calls the global rng.
-    # We want different implementations of _watermap 
-    # and internally called functions (especially random_land)
-    # to show the same rng behaviour and not contamine the state of the global rng
-    # should anyone else happen to rely on it.
     # This does only test that watermap leaves the rng in the state that the 
     # original implementation would have left it in and that a very small sample 
     # of results is the same as the original results.
@@ -26,7 +20,6 @@ class TestSimulation(unittest.TestCase):
     # have a finer grained picture.
 
     def test_watermap_rng_stabilty(self):
-
         seed=12345
         numpy.random.seed(seed)
 
@@ -56,8 +49,22 @@ def test_watermap_rng_stabilty(self):
         d = numpy.random.randint(0,100)
         self.assertEqual(d, 59)
 
+
+    def test_watermap_does_not_break_with_no_land(self):
+        seed=12345
+        numpy.random.seed(seed)
+
+        size = Size(16,8)
+
+        ocean = numpy.full((size.height, size.width), True, bool)
+
+        w = World("watermap",  size, seed, GenerationParameters(0, 1.0, 0))
+        w.ocean = ocean
+
+        data, t = WatermapSimulation._watermap(w, 200)
+
+
     def test_random_land_returns_only_land(self):
-
         size = Size(100,90)
 
         ocean = numpy.fromfunction(lambda y, x: y>=x, (size.height, size.width))

worldengine/model/world.py

@@ -397,7 +397,6 @@ def contains(self, pos):
     #
 
     def random_land(self, num_samples=1):
-
         if self.layers['ocean'].data.all():
             return None, None  # return invalid indices if there is no land at all
 

worldengine/simulations/hydrology.py

@@ -57,10 +57,21 @@ def droplet(world, pos, q, _watermap):
                 _watermap[y, x] += q
 
         _watermap_data = numpy.zeros((world.height, world.width), dtype=float)
-        for i in range(n):
-            x, y = world.random_land()  # will return None for x and y if no land exists
-            if x is not None and world.precipitations_at((x, y)) > 0:
-                droplet(world, (x, y), world.precipitations_at((x, y)), _watermap_data)
+
+        # This indirectly calls the global rng.
+        # We want different implementations of _watermap 
+        # and internally called functions (especially random_land)
+        # to show the same rng behaviour and not contamine the state of the global rng
+        # should anyone else happen to rely on it.
+
+        land_sample = world.random_land(n)
+
+        if land_sample[0] is not None:
+            for i in range(n):
+                x, y = land_sample[2*i], land_sample[2*i+1]
+                if world.precipitations_at((x, y)) > 0:
+                    droplet(world, (x, y), world.precipitations_at((x, y)), _watermap_data)
+
         ocean = world.layers['ocean'].data
         thresholds = dict()
         thresholds['creek'] = find_threshold_f(_watermap_data, 0.05, ocean=ocean)