add fall.max_opacity, fall.opaque properties & update snow texture & weather mix test

src/graphics/render/PrecipitationRenderer.cpp

@@ -127,7 +127,11 @@ void PrecipitationRenderer::render(
         {{0, 0, 1}, {1, 0, 0}},
     };
 
+    bool cutBack = glm::dot(camera.up, glm::vec3(0, 1, 0)) > 0.35f * camera.getFov();
     for (const auto& face : faces) {
+        if (glm::dot(camera.right, face.right) < 0.0f && cutBack) {
+            continue;
+        }
         for (int lx = -radius; lx <= radius; lx++) {
             for (int lz = depth; lz > 0; lz--) {
                 // Position calculations