feat(terrain): binary terrain files (.btf) made out of text terrain files (.txtf) named by terrain directives, checked against length and checksum of the text and loaded section by section when needed; -btf command line conversion; SBT files no longer generated, only loaded

scene/scene.h

@@ -45,6 +45,8 @@ struct scratch_data {
         std::vector<std::string> terrain_files; // files named by terrain directives; each one is loaded once
         std::size_t geometry_imported{ 0 }; // pieces of static geometry read from the text definitions so far
         std::size_t geometry_skipped{ 0 }; // pieces of static geometry left out so far, as provided by binary terrain
+        std::vector<std::string> terrain_textfiles; // terrain files (.txtf with binary .btf version) named by terrain directives so far
+        std::vector<std::string> terrain_binaryfiles; // binary versions of these, to be put to use once the scenery is initialized
     } binary;
 
     struct location_data {
@@ -78,6 +80,16 @@ struct scratch_data {
 	bool time_initialized { false };
 };
 
+struct terrain_source;
+
+// piece of a binary terrain file holding geometry of a single section, waiting to be loaded
+struct terrain_block {
+
+    std::shared_ptr<terrain_source> source; // the file and data shared by its pieces
+    std::uint64_t offset { 0 }; // location of the piece in the file
+    std::uint32_t size { 0 };
+};
+
 // basic element of rudimentary partitioning scheme for the section. fixed size, no further subdivision
 // TBD, TODO: replace with quadtree scheme?
 class basic_cell {
@@ -346,6 +358,9 @@ public:
 	// generates renderable version of held non-instanced geometry
     void
         create_geometry();
+    // loads geometry of the section kept in binary terrain files, if any is waiting
+    void
+        load_terrain();
 	void
 	    create_map_geometry(const gfx::geometrybank_handle handle);
 	void
@@ -374,6 +389,7 @@ public:
     // content
     cell_array m_cells; // partitioning scheme
     shapenode_sequence m_shapes; // large pieces of opaque geometry and (legacy) terrain
+    std::vector<terrain_block> m_terrain; // geometry in binary terrain files, loaded when the section comes into use
     // TODO: implement dedicated, higher fidelity, fixed resolution terrain mesh item
 	// gfx renderer data
     gfx::geometrybank_handle m_geometrybank;
@@ -481,6 +497,9 @@ public:
 	    create_map_geometry();
 	void
 	    update_poi_geometry();
+    // loads all geometry kept in binary terrain files which wasn't needed so far
+    void
+        load_terrain();
     basic_section* get_section(size_t section)
 	    { return m_sections[section]; }
 	gfx::geometrybank_handle