Reduce octaves and add noise for 'jagged' edges

src/openrct2/util/Util.cpp

@@ -423,6 +423,15 @@ uint32_t util_rand()
     return _prng();
 }
 
+// Returns a random floating point number from the Standard Normal Distribution; mean of 0 and standard deviation of 1.
+// TODO: In C++20 this can be templated, where the standard deviation is passed as a value template argument.
+float util_rand_normal_distributed()
+{
+    thread_local std::mt19937 _prng{ std::random_device{}() };
+    thread_local std::normal_distribution<float> _distributor{ 0.0f, 1.0f };
+    return _distributor(_prng);
+}
+
 constexpr size_t CHUNK = 128 * 1024;
 
 // Compress the source to gzip-compatible stream, write to dest.

src/openrct2/util/Util.h

@@ -42,6 +42,7 @@ char* strcasestr(const char* haystack, const char* needle);
 bool str_is_null_or_empty(const char* str);
 
 uint32_t util_rand();
+float util_rand_normal_distributed();
 
 bool util_gzip_compress(FILE* source, FILE* dest);
 std::vector<uint8_t> Gzip(const void* data, const size_t dataLen);

src/openrct2/world/MapGen.cpp

@@ -338,8 +338,10 @@ static void mapgen_place_trees()
                 continue;
 
             // Use fractal noise to group tiles that are likely to spawn trees together
-            float noiseValue = std::clamp(fractal_noise(x, y, 0.025f, 8, 2.0f, 0.65f), -1.0f, 1.0f);
-            if (noiseValue < 0.0f)
+            float noiseValue = fractal_noise(x, y, 0.025f, 2, 2.0f, 0.65f);
+            // Reduces the range to rarely stray further than 0.5 from the mean.
+            float noiseOffset = util_rand_normal_distributed() * 0.25f;
+            if (noiseValue < noiseOffset)
                 continue;
 
             ObjectEntryIndex treeObjectEntryIndex = OBJECT_ENTRY_INDEX_NULL;