feat(track): 3D sleepers and switch timbers, blade heel and throw from templates, one rail carving pass

- sleepers3d / sleepers3dplain / sleepers3dbed in eu07.ini: timbers put together from the begin, main and end parts of a model
  and stretched to their length, plain sleepers of their own model; tracks whose plain sleepers would touch are laid as one
  cluster, lines of timbers led by priority and turned to the bisectors of frogs and crossings at a limited rate, whole timbers
  under crossings, split ones between tracks with room to part them, gaps filled per rail and overlaps shortened or dropped;
  clusters worked out in a background thread while driving, on demand in the editor
- the ballast can be left out under the beams (sleepers3dbed no)
- blades get their heel and throw from the switch template or blades <heel> <throw> in the scenery; blades of double switches
  run on into the track linking them to the next switch
- rail cutting at frogs, wing rails, movable noses and switch crossings done by one carving pass (RailCarve)
- tint of the rail treads applied to the colour only, without the matte band at the frog
- a switch trailed through with a movable nose set the other way derails the vehicle
- self-tests: sleepercheck, sharedzones, beamsnear, throw, sleepersbg

rendering/opengl33renderer.h

@@ -18,6 +18,7 @@ http://mozilla.org/MPL/2.0/.
 #include "simulation/simulationenvironment.h"
 #include "scene/scene.h"
 #include "world/MemCell.h"
+#include "world/TrackSleepers.h"
 #include "rendering/lightarray.h"
 #include "vr/vr_interface.h"
 #include "gl/ubo.h"
@@ -75,6 +76,8 @@ class opengl33_renderer : public gfx_renderer {
 	// provides direct access to vertex data of specfied chunk
 	gfx::userdata_array const &
 		UserData( gfx::geometry_handle const &Geometry ) const override;
+	int
+		Primitive( gfx::geometry_handle const &Geometry ) const override;
     // material methods
     material_handle
         Fetch_Material( std::string const &Filename, bool const Loadnow = true ) override;
@@ -310,6 +313,9 @@ class opengl33_renderer : public gfx_renderer {
 	// no-op if the track has no sleepermodel, Global.SleeperDistance is 0, or the camera is beyond
 	// Global.SleeperDistance from the track origin.
 	void Render_Sleepers( TTrack *Track );
+	// renders the sleepers and switch timbers of the tracks in range (TTrack::m_sleepers3d), laying them first where they're out of date.
+	// the parts of the model are drawn in instanced batches for the whole run of tracks, the runs of beams out of sight left out
+	void Render_Timbers( scene::basic_cell::path_sequence::const_iterator First, scene::basic_cell::path_sequence::const_iterator Last );
 	bool Render_cab(TDynamicObject const *Dynamic, float const Lightlevel, bool const Alpha = false);
     bool Render_interior( bool const Alpha = false );
     bool Render_lowpoly( TDynamicObject *Dynamic, float const Squaredistance, bool const Setup, bool const Alpha = false );
@@ -465,6 +471,15 @@ class opengl33_renderer : public gfx_renderer {
 	// than a single regular draw. The vertex shader reads per-instance modelview
 	// from instance_ubo[gl_InstanceID]. Reset to 0 by Render_Instanced() on exit.
 	std::size_t m_current_instance_count { 0 };
+	// camera-space transforms of the sleepers and timbers drawn by Render_Timbers, by the model and its part or its level of
+	// detail; kept from frame to frame to reuse their allocations
+	struct timber_bucket {
+		track_sleepers::beam_model const *model { nullptr };
+		int part { -1 }; // of a model put together from parts; -1: the whole model
+		float band { 0.f }; // the squared distance the level of detail of the whole model is seen from
+		std::vector<glm::mat4> instances;
+	};
+	std::vector<timber_bucket> m_timberbuckets;
 	// persistent scratch buffer for Render_Instanced(): holds the per-instance
 	// camera-space root modelview matrices for the batch currently being built.
 	// Kept as a member rather than a function-local so its heap allocation is