Make marching cubes skirts an option in VoxelMesherDMC, also use more C++11 initializers

meshers/dmc/voxel_mesher_dmc.cpp

@@ -1426,11 +1426,6 @@ void polygonize_volume_directly(const VoxelBuffer &voxels, Vector3i min, Vector3
 #define BUILD_OCTREE_BOTTOM_UP
 
 VoxelMesherDMC::VoxelMesherDMC() {
-
-	_geometric_error = 0.1;
-	_mesh_mode = MESH_NORMAL;
-	_octree_mode = OCTREE_BOTTOM_UP;
-	_stats = { 0 };
 }
 
 void VoxelMesherDMC::set_mesh_mode(MeshMode mode) {
@@ -1457,6 +1452,14 @@ float VoxelMesherDMC::get_geometric_error() const {
 	return _geometric_error;
 }
 
+void VoxelMesherDMC::set_seam_mode(SeamMode mode) {
+	_seam_mode = mode;
+}
+
+VoxelMesherDMC::SeamMode VoxelMesherDMC::get_seam_mode() const {
+	return _seam_mode;
+}
+
 void VoxelMesherDMC::build(VoxelMesher::Output &output, const VoxelBuffer &voxels, int padding) {
 
 	// Requirements:
@@ -1481,7 +1484,15 @@ void VoxelMesherDMC::build(VoxelMesher::Output &output, const VoxelBuffer &voxel
 	ERR_FAIL_COND(voxels.get_size().z < chunk_size + padding * 2);
 
 	// TODO Option for this in case LOD is not used
-	bool skirts_enabled = true;
+	bool skirts_enabled = _seam_mode == SEAM_MARCHING_SQUARE_SKIRTS;
+	// Marching square skirts are a cheap way to hide LOD cracks,
+	// however they might still be visible because of shadow mapping, and cause potential issues when used for physics.
+	// Maybe a shader with a `light()` function can prevent shadows from being applied to these,
+	// but in longer term, proper seams remain a better solution.
+	// Unfortunately, such seams require the ability to quickly swap index buffers of the mesh using OpenGL/Vulkan,
+	// which is not possible with current Godot's VisualServer without forking the whole lot (dang!),
+	// and we are forced to at least re-upload the mesh entirely or have 16 versions of it just swapping seams...
+	// So we can't improve this further until Godot's API gives us that possibility, or other approaches like skirts need to be taken.
 
 	// Construct an intermediate to handle padding transparently
 	dmc::VoxelAccess voxels_access(voxels, Vector3i(padding));
@@ -1601,6 +1612,9 @@ void VoxelMesherDMC::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("set_geometric_error", "error"), &VoxelMesherDMC::set_geometric_error);
 	ClassDB::bind_method(D_METHOD("get_geometric_error"), &VoxelMesherDMC::get_geometric_error);
 
+	ClassDB::bind_method(D_METHOD("set_seam_mode", "mode"), &VoxelMesherDMC::set_seam_mode);
+	ClassDB::bind_method(D_METHOD("get_seam_mode"), &VoxelMesherDMC::get_seam_mode);
+
 	ClassDB::bind_method(D_METHOD("get_stats"), &VoxelMesherDMC::get_stats);
 
 	BIND_ENUM_CONSTANT(MESH_NORMAL);
@@ -1611,4 +1625,7 @@ void VoxelMesherDMC::_bind_methods() {
 	BIND_ENUM_CONSTANT(OCTREE_BOTTOM_UP);
 	BIND_ENUM_CONSTANT(OCTREE_TOP_DOWN);
 	BIND_ENUM_CONSTANT(OCTREE_NONE);
+
+	BIND_ENUM_CONSTANT(SEAM_NONE);
+	BIND_ENUM_CONSTANT(SEAM_MARCHING_SQUARE_SKIRTS);
 }

meshers/dmc/voxel_mesher_dmc.h

@@ -46,10 +46,7 @@ struct OctreeNode {
 struct DualCell {
 	Vector3 corners[8];
 	HermiteValue values[8];
-	bool has_values;
-
-	DualCell() :
-			has_values(false) {}
+	bool has_values = false;
 
 	inline void set_corner(int i, Vector3 vertex, HermiteValue value) {
 		CRASH_COND(i < 0 || i >= 8);
@@ -64,6 +61,7 @@ struct DualGrid {
 
 } // namespace dmc
 
+// Mesher extending Marching Cubes using a dual grid.
 class VoxelMesherDMC : public VoxelMesher {
 	GDCLASS(VoxelMesherDMC, VoxelMesher)
 public:
@@ -76,12 +74,20 @@ public:
 		MESH_DEBUG_DUAL_GRID
 	};
 
+	// TODO Rename SimplifyMode because octree isn't the only way
 	enum OctreeMode {
 		OCTREE_BOTTOM_UP,
 		OCTREE_TOP_DOWN,
 		OCTREE_NONE
 	};
 
+	enum SeamMode {
+		SEAM_NONE, // No seam management
+		SEAM_MARCHING_SQUARE_SKIRTS, // Marching square skirts
+		// SEAM_OVERLAP // Polygonize extra voxels with lower isolevel
+		// SEAM_JUNCTION_TRIANGLES // Extra triangles for alternate borders, requires index buffer switching
+	};
+
 	VoxelMesherDMC();
 
 	void set_mesh_mode(MeshMode mode);
@@ -93,6 +99,9 @@ public:
 	void set_geometric_error(real_t geometric_error);
 	float get_geometric_error() const;
 
+	void set_seam_mode(SeamMode mode);
+	SeamMode get_seam_mode() const;
+
 	void build(VoxelMesher::Output &output, const VoxelBuffer &voxels, int padding) override;
 	int get_minimum_padding() const override;
 
@@ -105,15 +114,16 @@ private:
 	dmc::MeshBuilder _mesh_builder;
 	dmc::DualGrid _dual_grid;
 	dmc::OctreeNodePool _octree_node_pool;
-	real_t _geometric_error;
-	MeshMode _mesh_mode;
-	OctreeMode _octree_mode;
+	real_t _geometric_error = 0.1;
+	MeshMode _mesh_mode = MESH_NORMAL;
+	OctreeMode _octree_mode = OCTREE_BOTTOM_UP;
+	SeamMode _seam_mode = SEAM_NONE;
 
 	struct Stats {
-		real_t octree_build_time;
-		real_t dualgrid_derivation_time;
-		real_t meshing_time;
-		real_t commit_time;
+		real_t octree_build_time = 0;
+		real_t dualgrid_derivation_time = 0;
+		real_t meshing_time = 0;
+		real_t commit_time = 0;
 	};
 
 	Stats _stats;
@@ -121,5 +131,6 @@ private:
 
 VARIANT_ENUM_CAST(VoxelMesherDMC::OctreeMode)
 VARIANT_ENUM_CAST(VoxelMesherDMC::MeshMode)
+VARIANT_ENUM_CAST(VoxelMesherDMC::SeamMode)
 
 #endif // VOXEL_MESHER_DMC_H

terrain/voxel_mesh_updater.cpp

@@ -16,6 +16,7 @@ VoxelMeshUpdater::VoxelMeshUpdater(Ref<VoxelLibrary> library, MeshingParams para
 		_dmc_mesher.instance();
 		_dmc_mesher->set_geometric_error(0.05);
 		_dmc_mesher->set_octree_mode(VoxelMesherDMC::OCTREE_NONE);
+		_dmc_mesher->set_seam_mode(VoxelMesherDMC::SEAM_MARCHING_SQUARE_SKIRTS);
 	}
 
 	_input_mutex = Mutex::create();