From 5b981712830767d7d9c4983175d662b5c8aa6c95 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Thu, 9 Apr 2026 15:18:19 +0300
Subject: [PATCH] Weather sim v2: use a fixed initial wind field + a small
 noise for all 8 climate snapshots

---
 examples/weather_v2.cpp | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/examples/weather_v2.cpp b/examples/weather_v2.cpp
index 6deba88c..b6409b30 100644
--- a/examples/weather_v2.cpp
+++ b/examples/weather_v2.cpp
@@ -44,7 +44,7 @@ auto make_perlin(random::generator & rng, int min_octave, int max_octave, float
 	return pcg::fractal<pcg::perlin<float, 2>>(std::move(octaves), std::move(weights));
 }
 
-void make_random_vector_field(random::generator & rng, util::ndarray<math::vector<float, 2>, 2> & result, int min_octave, int max_octave, float scale)
+void add_random_vector_field(random::generator & rng, util::ndarray<math::vector<float, 2>, 2> & result, int min_octave, int max_octave, float scale)
 {
 	auto noise_1 = make_perlin(rng, min_octave, max_octave, 2.f);
 	auto noise_2 = make_perlin(rng, min_octave, max_octave, 2.f);
@@ -54,7 +54,7 @@ void make_random_vector_field(random::generator & rng, util::ndarray<math::vecto
 		for (int x = 0; x < result.width(); ++x)
 		{
 			math::point p{(x + 0.5f) / result.height(), (y + 0.5f) / result.width()};
-			result(x, y) = math::normalized(math::vector{2.f * noise_1(p) - 1.f, 2.f * noise_2(p) - 1.f}) * scale;
+			result(x, y) += math::normalized(math::vector{2.f * noise_1(p) - 1.f, 2.f * noise_2(p) - 1.f}) * scale;
 		}
 	}
 }
@@ -176,7 +176,8 @@ struct solver
 	int stage = 0;
 	bool finished = false;
 
-	solver(util::ndarray<float, 2> const & terrain,	random::generator & rng, int season, int day_night, climate_snapshot & snapshot)
+	solver(util::ndarray<float, 2> const & terrain,	random::generator & rng, int season, int day_night, climate_snapshot & snapshot,
+		util::ndarray<math::vector<float, 2>, 2> const & base_wind_velocity)
 		: terrain(terrain)
 		, rng(rng)
 		, season(season)
@@ -191,7 +192,8 @@ struct solver
 		snapshot.humidity.resize({N, N}, 0.f);
 		new_humidity.resize({N, N}, 0.f);
 
-		make_random_vector_field(rng, initial_random_wind_velocity, 3, 6, 0.005f);
+		initial_random_wind_velocity = base_wind_velocity.copy();
+		add_random_vector_field(rng, initial_random_wind_velocity, 3, 6, 0.002f);
 
 		for (int y = 0; y < N; ++y)
 			for (int x = 0; x < N; ++x)
@@ -398,6 +400,8 @@ struct weather_app
 	// 1 - Day
 	int day_night = 0;
 
+	util::ndarray<math::vector<float, 2>, 2> base_wind_velocity;
+
 	climate_snapshot snapshots[4][2];
 	climate_snapshot average;
 	climate_snapshot display_snapshot;
@@ -417,13 +421,17 @@ struct weather_app
 		simulation_box = {{{0.f, N}, {0.f, N}}};
 
 		terrain.resize({N, N}, 0.f);
-		auto heightmap = gfx::read_image<std::uint8_t>(io::file_istream{std::filesystem::path{PSEMEK_EXAMPLES_DIR} / "heightmap_seed_3.png"});
+		auto heightmap = gfx::read_image<std::uint8_t>(io::file_istream{std::filesystem::path{PSEMEK_EXAMPLES_DIR} / "heightmap_seed_1.png"});
 		for (int y = 0; y < N; ++y)
 			for (int x = 0; x < N; ++x)
 				terrain(x, y) = ((heightmap(x, y) / 255.f) * 2048.f - 512.f) / 1024.f;
 
 		biomes_map = gfx::read_image<gfx::color_rgba>(io::file_istream{std::filesystem::path{PSEMEK_EXAMPLES_DIR} / "biomes.png"});
 
+		base_wind_velocity.resize({N, N}, math::vector{0.f, 0.f});
+
+		add_random_vector_field(rng, base_wind_velocity, 3, 6, 0.003f);
+
 		context.vsync(false);
 	}
 
@@ -473,13 +481,13 @@ struct weather_app
 		}
 
 		if (!solver && season < 4)
-			solver.emplace(terrain, rng, season, day_night, snapshots[season][day_night]);
+			solver.emplace(terrain, rng, season, day_night, snapshots[season][day_night], base_wind_velocity);
 
 		if (!paused)
 		{
 			if (solver)
 			{
-				for (int i = 0; i < 16; ++i)
+				for (int i = 0; i < 64; ++i)
 				{
 					solver->step();
 					if (solver->finished)
@@ -488,7 +496,7 @@ struct weather_app
 			}
 			else if (season == 4 && !rivers.queue.empty())
 			{
-				for (int i = 0; i < 16; ++i)
+				for (int i = 0; i < 64; ++i)
 				{
 					propagate_rivers();
 					if (rivers.queue.empty())