Reorganize source files into logical subdirectories

Co-authored-by: Hirek193 <23196899+Hirek193@users.noreply.github.com>

rendering/precipitation.h

@@ -0,0 +1,42 @@
+/*
+This Source Code Form is subject to the
+terms of the Mozilla Public License, v.
+2.0. If a copy of the MPL was not
+distributed with this file, You can
+obtain one at
+http://mozilla.org/MPL/2.0/.
+*/
+
+#pragma	once
+
+// based on "Rendering Falling Rain and Snow"
+// by Niniane Wang, Bretton Wade
+
+class basic_precipitation {
+
+public:
+// constructors
+    basic_precipitation() = default;
+// destructor
+	~basic_precipitation();
+// methods
+    bool
+        init();
+    void
+        update();
+    float
+        get_textureoffset() const;
+
+    glm::dvec3 m_cameramove{ 0.0 };
+
+private:
+// members
+    float m_textureoffset { 0.f };
+    float m_moverate { 30 * 0.001f };
+    float m_moverateweathertypefactor { 1.f }; // medium-dependent; 1.0 for snow, faster for rain
+    glm::dvec3 m_camerapos { 0.0 };
+    bool m_freeflymode { true };
+    bool m_windowopen { true };
+    int m_activecab{ 0 };
+    glm::dvec3 m_cabcameramove{ 0.0 };
+};