refactor: river (#10)

* fix: correct snowy grass block texture

* refactor: river generation

* fix: water placement error due to interpolation

* perf: improve river naturalness

* feat: add river tab item

* fix: path truncation

src/gameplay/river_worm.cpp

@@ -0,0 +1,53 @@
+#include "Cubed/gameplay/river_worm.hpp"
+
+#include "Cubed/constants.hpp"
+
+namespace Cubed {
+RiverWorm::RiverWorm() {}
+
+std::unordered_map<unsigned, RiverPath>& RiverWorm::paths() { return m_paths; }
+
+void RiverWorm::init(unsigned world_seed) {
+    m_seed = world_seed;
+    m_sum = 0;
+    m_random.init(m_seed);
+}
+
+void RiverWorm::reload(unsigned world_seed) {
+    m_seed = world_seed;
+    m_paths.clear();
+    init(world_seed);
+}
+
+void RiverWorm::add_path(const glm::vec3& pos, unsigned chunk_seed) {
+    m_paths.emplace(chunk_seed, RiverPath{m_seed, m_sum, pos});
+    m_sum++;
+}
+
+void RiverWorm::try_to_add_path(const ChunkPos& chunk_pos,
+                                unsigned chunk_seed) {
+    auto it = m_paths.find(chunk_seed);
+    if (it != m_paths.end()) {
+        return;
+    }
+    Random random{chunk_seed};
+    if (random.random_bool(static_cast<double>(m_probability))) {
+        const int CHUNK_MIN_X = chunk_pos.x * CHUNK_SIZE;
+        const int CHUNK_MIN_Z = chunk_pos.z * CHUNK_SIZE;
+        const int CHUNK_MAX_X = CHUNK_MIN_X + SIZE_X - 1;
+        const int CHUNK_MAX_Z = CHUNK_MIN_Z + SIZE_Z - 1;
+        int x = random.random_int(CHUNK_MIN_X, CHUNK_MAX_X);
+        int y = SEA_LEVEL + 2;
+        int z = random.random_int(CHUNK_MIN_Z, CHUNK_MAX_Z);
+        add_path(glm::vec3{x, y, z}, chunk_seed);
+    }
+}
+
+void RiverWorm::cleanup_finished_rivers() {
+    std::erase_if(m_paths,
+                  [](const auto& kv) { return kv.second.is_finished(); });
+}
+
+int RiverWorm::river_sum() const { return m_sum; }
+float& RiverWorm::river_probability() { return m_probability; }
+} // namespace Cubed