godot_voxel/meshers/dmc/voxel_mesher_dmc.cpp

#include "voxel_mesher_dmc.h"
#include "../../cube_tables.h"
#include "marching_cubes_tables.h"
#include "mesh_builder.h"
#include "octree_tables.h"
#include <core/os/os.h>

// Dual marching cubes
// Algorithm taken from https://www.volume-gfx.com/volume-rendering/dual-marching-cubes/

namespace dmc {

// Surface is defined when isolevel crosses 0
const float SURFACE_ISO_LEVEL = 0.0;

const float NEAR_SURFACE_FACTOR = 2.0;
const float SQRT3 = 1.7320508075688772;

// Helper to access padded voxel data
struct VoxelAccess {

	const VoxelBuffer &buffer;
	const Vector3i offset;

	VoxelAccess(const VoxelBuffer &p_buffer, Vector3i p_offset) :
			buffer(p_buffer),
			offset(p_offset) {}

	inline HermiteValue get_hermite_value(int x, int y, int z) const {
		return dmc::get_hermite_value(buffer, x + offset.x, y + offset.y, z + offset.z);
	}

	inline HermiteValue get_interpolated_hermite_value(Vector3 pos) const {
		pos.x += offset.x;
		pos.y += offset.y;
		pos.z += offset.z;
		return dmc::get_interpolated_hermite_value(buffer, pos);
	}
};

bool can_split(Vector3i node_origin, int node_size, const VoxelAccess &voxels, float geometric_error) {

	if (node_size == 1) {
		// Voxel resolution, can't split further
		return false;
	}

	Vector3i origin = node_origin + voxels.offset;
	int step = node_size;
	int channel = VoxelBuffer::CHANNEL_ISOLEVEL;

	// Don't split if nothing is inside, i.e isolevel distance is greater than the size of the cube we are in
	Vector3i center_pos = node_origin + Vector3i(node_size / 2);
	HermiteValue center_value = voxels.get_hermite_value(center_pos.x, center_pos.y, center_pos.z);
	if (Math::abs(center_value.value) > SQRT3 * (float)node_size) {
		return false;
	}

	// Fighting with Clang-format here /**/

	float v0 = voxels.buffer.get_voxel_f(origin.x, /*  */ origin.y, /*  */ origin.z, /*  */ channel); // 0
	float v1 = voxels.buffer.get_voxel_f(origin.x + step, origin.y, /*  */ origin.z, /*  */ channel); // 1
	float v2 = voxels.buffer.get_voxel_f(origin.x + step, origin.y, /*  */ origin.z + step, channel); // 2
	float v3 = voxels.buffer.get_voxel_f(origin.x, /*  */ origin.y, /*  */ origin.z + step, channel); // 3

	float v4 = voxels.buffer.get_voxel_f(origin.x, /*  */ origin.y + step, origin.z, /*  */ channel); // 4
	float v5 = voxels.buffer.get_voxel_f(origin.x + step, origin.y + step, origin.z, /*  */ channel); // 5
	float v6 = voxels.buffer.get_voxel_f(origin.x + step, origin.y + step, origin.z + step, channel); // 6
	float v7 = voxels.buffer.get_voxel_f(origin.x, /*  */ origin.y + step, origin.z + step, channel); // 7

	int hstep = step / 2;

	Vector3i positions[19] = {
		// Starting from point 8
		Vector3i(origin.x + hstep, /**/ origin.y, /*        */ origin.z), // 8
		Vector3i(origin.x + step, /* */ origin.y, /*        */ origin.z + hstep), // 9
		Vector3i(origin.x + hstep, /**/ origin.y, /*        */ origin.z + step), // 10
		Vector3i(origin.x, /*        */ origin.y, /*        */ origin.z + hstep), // 11

		Vector3i(origin.x, /*        */ origin.y + hstep, /**/ origin.z), // 12
		Vector3i(origin.x + step, /* */ origin.y + hstep, /**/ origin.z), // 13
		Vector3i(origin.x + step, /* */ origin.y + hstep, /**/ origin.z + step), // 14
		Vector3i(origin.x, /*        */ origin.y + hstep, /**/ origin.z + step), // 15

		Vector3i(origin.x + hstep, /**/ origin.y + step, /* */ origin.z), // 16
		Vector3i(origin.x + step, /* */ origin.y + step, /* */ origin.z + hstep), // 17
		Vector3i(origin.x + hstep, /**/ origin.y + step, /* */ origin.z + step), // 18
		Vector3i(origin.x, /*        */ origin.y + step, /* */ origin.z + hstep), // 19

		Vector3i(origin.x + hstep, /**/ origin.y, /*        */ origin.z + hstep), // 20
		Vector3i(origin.x + hstep, /**/ origin.y + hstep, /**/ origin.z), // 21
		Vector3i(origin.x + step, /* */ origin.y + hstep, /**/ origin.z + hstep), // 22
		Vector3i(origin.x + hstep, /**/ origin.y + hstep, /**/ origin.z + step), // 23
		Vector3i(origin.x, /*        */ origin.y + hstep, /**/ origin.z + hstep), // 24
		Vector3i(origin.x + hstep, /**/ origin.y + step, /* */ origin.z + hstep), // 25
		Vector3i(origin.x + hstep, /**/ origin.y + hstep, /**/ origin.z + hstep) // 26
	};

	Vector3 positions_ratio[19] = {
		Vector3(0.5, 0.0, 0.0),
		Vector3(1.0, 0.0, 0.5),
		Vector3(0.5, 0.0, 1.0),
		Vector3(0.0, 0.0, 0.5),

		Vector3(0.0, 0.5, 0.0),
		Vector3(1.0, 0.5, 0.0),
		Vector3(1.0, 0.5, 1.0),
		Vector3(0.0, 0.5, 1.0),

		Vector3(0.5, 1.0, 0.0),
		Vector3(1.0, 1.0, 0.5),
		Vector3(0.5, 1.0, 1.0),
		Vector3(0.0, 1.0, 0.5),

		Vector3(0.5, 0.0, 0.5),
		Vector3(0.5, 0.5, 0.0),
		Vector3(1.0, 0.5, 0.5),
		Vector3(0.5, 0.5, 1.0),
		Vector3(0.0, 0.5, 0.5),
		Vector3(0.5, 1.0, 0.5),
		Vector3(0.5, 0.5, 0.5)
	};

	float error = 0.0;

	for (int i = 0; i < 19; ++i) {

		Vector3i pos = positions[i];

		HermiteValue value = get_hermite_value(voxels.buffer, pos.x, pos.y, pos.z);

		float interpolated_value = ::interpolate(v0, v1, v2, v3, v4, v5, v6, v7, positions_ratio[i]);

		float gradient_magnitude = value.gradient.length();
		if (gradient_magnitude < FLT_EPSILON) {
			gradient_magnitude = 1.0;
		}
		error += Math::abs(value.value - interpolated_value) / gradient_magnitude;
		if (error >= geometric_error) {
			return true;
		}
	}

	return false;
}

inline Vector3 get_center(const OctreeNode *node) {
	return node->origin.to_vec3() + 0.5 * Vector3(node->size, node->size, node->size);
}

class OctreeBuilderTopDown {
public:
	OctreeBuilderTopDown(const VoxelAccess &voxels, float geometry_error, OctreeNodePool &pool) :
			_voxels(voxels),
			_geometry_error(geometry_error),
			_pool(pool) {
	}

	OctreeNode *build(Vector3i origin, int size) {
		OctreeNode *root = _pool.create();
		root->origin = origin;
		root->size = size;
		build(root);
		return root;
	}

private:
	void build(OctreeNode *node) {
		if (can_split(node->origin, node->size, _voxels, _geometry_error)) {
			split(node);
			for (int i = 0; i < 8; ++i) {
				build(node->children[i]);
			}
		} else {
			node->center_value = _voxels.get_interpolated_hermite_value(get_center(node));
		}
	}

	void split(OctreeNode *node) {

		CRASH_COND(node->has_children());
		CRASH_COND(node->size == 1);

		for (int i = 0; i < 8; ++i) {

			OctreeNode *child = _pool.create();
			const int *v = OctreeTables::g_octant_position[i];
			child->size = node->size / 2;
			child->origin = node->origin + Vector3i(v[0], v[1], v[2]) * child->size;

			node->children[i] = child;
		}
	}

private:
	const VoxelAccess &_voxels;
	const float _geometry_error;
	OctreeNodePool &_pool;
};

// Builds the octree bottom-up, to ensure that no detail can be missed by a top-down approach.
class OctreeBuilderBottomUp {
public:
	OctreeBuilderBottomUp(const VoxelAccess &voxels, float geometry_error, OctreeNodePool &pool) :
			_voxels(voxels),
			_geometry_error(geometry_error),
			_pool(pool) {
	}

	OctreeNode *build(Vector3i node_origin, int node_size) const {

		OctreeNode *children[8] = { nullptr };
		bool any_node = false;

		// Go all the way down, except leaves because we can't reason bottom-up on them
		if (node_size > 2) {
			for (int i = 0; i < 8; ++i) {
				const int *dir = OctreeTables::g_octant_position[i];
				int child_size = node_size / 2;
				children[i] = build(node_origin + child_size * Vector3i(dir[0], dir[1], dir[2]), child_size);
				any_node |= children[i] != nullptr;
			}
		}

		OctreeNode *node = nullptr;

		if (!any_node) {
			// No nodes, test if the 8 octants are worth existing (this could be leaves)
			if (can_split(node_origin, node_size, _voxels, _geometry_error)) {

				node = _pool.create();
				node->origin = node_origin;
				node->size = node_size;

				// Create all 8 children
				for (int i = 0; i < 8; ++i) {
					node->children[i] = create_child(node_origin, node_size, i);
				}
			}
			// If no splitting... then we return null.
			// If the parent iteration gets all children null this way,
			// it will allow detail reduction recursively upwards.

		} else {
			// Some child nodes were deemed worthy of existence,
			// create their siblings at the same detail level

			node = _pool.create();
			node->origin = node_origin;
			node->size = node_size;

			for (int i = 0; i < 8; ++i) {
				if (children[i] != nullptr) {
					node->children[i] = children[i];
				} else {
					node->children[i] = create_child(node_origin, node_size, i);
				}
			}
		}

		return node;
	}

private:
	inline OctreeNode *create_child(Vector3i parent_origin, int parent_size, int i) const {
		const int *dir = OctreeTables::g_octant_position[i];
		OctreeNode *child = _pool.create();
		child->size = parent_size / 2;
		child->origin = parent_origin + child->size * Vector3i(dir[0], dir[1], dir[2]);
		child->center_value = _voxels.get_interpolated_hermite_value(get_center(child));
		return child;
	}

private:
	const VoxelAccess &_voxels;
	const float _geometry_error;
	OctreeNodePool &_pool;
};

template <typename Action_T>
void foreach_node(OctreeNode *root, Action_T &a, int depth = 0) {
	a(root, depth);
	for (int i = 0; i < 8; ++i) {
		if (root->children[i]) {
			foreach_node(root->children[i], a, depth + 1);
		}
	}
}

Array generate_debug_octree_mesh(OctreeNode *root) {

	struct GetMaxDepth {
		int max_depth;
		void operator()(OctreeNode *_, int depth) {
			if (depth > max_depth) {
				max_depth = depth;
			}
		}
	};

	struct Arrays {
		PoolVector3Array positions;
		PoolColorArray colors;
		PoolIntArray indices;
	};

	struct AddCube {
		Arrays *arrays;
		int max_depth;

		void operator()(OctreeNode *node, int depth) {

			float shrink = depth * 0.005;
			Vector3 o = node->origin.to_vec3() + Vector3(shrink, shrink, shrink);
			float s = node->size - 2.0 * shrink;

			Color col(1.0, (float)depth / (float)max_depth, 0.0);

			int vi = arrays->positions.size();

			for (int i = 0; i < Cube::CORNER_COUNT; ++i) {
				arrays->positions.push_back(o + s * Cube::g_corner_position[i]);
				arrays->colors.push_back(col);
			}

			for (int i = 0; i < Cube::EDGE_COUNT; ++i) {
				arrays->indices.push_back(vi + Cube::g_edge_corners[i][0]);
				arrays->indices.push_back(vi + Cube::g_edge_corners[i][1]);
			}
		}
	};

	GetMaxDepth get_max_depth;
	foreach_node(root, get_max_depth);

	Arrays arrays;
	AddCube add_cube;
	add_cube.arrays = &arrays;
	add_cube.max_depth = get_max_depth.max_depth;
	foreach_node(root, add_cube);

	if (arrays.positions.size() == 0) {
		return Array();
	}

	Array surface;
	surface.resize(Mesh::ARRAY_MAX);
	surface[Mesh::ARRAY_VERTEX] = arrays.positions;
	surface[Mesh::ARRAY_COLOR] = arrays.colors;
	surface[Mesh::ARRAY_INDEX] = arrays.indices;

	return surface;
}

Array generate_debug_dual_grid_mesh(const DualGrid &grid) {

	PoolVector3Array positions;
	PoolIntArray indices;

	for (int i = 0; i < grid.cells.size(); ++i) {

		const DualCell &cell = grid.cells[i];

		int vi = positions.size();

		for (int j = 0; j < 8; ++j) {
			//			Vector3 p = Vector3(g_octant_position[j][0], g_octant_position[j][1], g_octant_position[j][2]);
			//			Vector3 n = (Vector3(0.5, 0.5, 0.5) - p).normalized();
			positions.push_back(cell.corners[j]); // + n * 0.01);
		}

		for (int j = 0; j < Cube::EDGE_COUNT; ++j) {
			indices.push_back(vi + Cube::g_edge_corners[j][0]);
			indices.push_back(vi + Cube::g_edge_corners[j][1]);
		}
	}

	if (positions.size() == 0) {
		return Array();
	}

	Array surface;
	surface.resize(Mesh::ARRAY_MAX);
	surface[Mesh::ARRAY_VERTEX] = positions;
	surface[Mesh::ARRAY_INDEX] = indices;

	return surface;
}

inline bool is_border_left(const OctreeNode *node) {
	return node->origin.x == 0;
}

inline bool is_border_right(const OctreeNode *node, int root_size) {
	return node->origin.x + node->size == root_size;
}

inline bool is_border_bottom(const OctreeNode *node) {
	return node->origin.y == 0;
}

inline bool is_border_top(const OctreeNode *node, int root_size) {
	return node->origin.y + node->size == root_size;
}

inline bool is_border_back(const OctreeNode *node) {
	return node->origin.z == 0;
}

inline bool is_border_front(const OctreeNode *node, int root_size) {
	return node->origin.z + node->size == root_size;
}

inline Vector3 get_center_back(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size * 0.5;
	p.y += node->size * 0.5;
	return p;
}

inline Vector3 get_center_front(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size * 0.5;
	p.y += node->size * 0.5;
	p.z += node->size;
	return p;
}

inline Vector3 get_center_left(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.y += node->size * 0.5;
	p.z += node->size * 0.5;
	return p;
}

inline Vector3 get_center_right(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size;
	p.y += node->size * 0.5;
	p.z += node->size * 0.5;
	return p;
}

inline Vector3 get_center_top(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size * 0.5;
	p.y += node->size;
	p.z += node->size * 0.5;
	return p;
}

inline Vector3 get_center_bottom(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size * 0.5;
	p.z += node->size * 0.5;
	return p;
}

inline Vector3 get_center_back_top(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size * 0.5;
	p.y += node->size;
	return p;
}

inline Vector3 get_center_back_bottom(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size * 0.5;
	return p;
}

inline Vector3 get_center_front_top(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size * 0.5;
	p.y += node->size;
	p.z += node->size;
	return p;
}

inline Vector3 get_center_front_bottom(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size * 0.5;
	p.z += node->size;
	return p;
}

inline Vector3 get_center_left_top(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.y += node->size;
	p.z += node->size * 0.5;
	return p;
}

inline Vector3 get_center_left_bottom(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.z += node->size * 0.5;
	return p;
}

inline Vector3 get_center_right_top(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size;
	p.y += node->size;
	p.z += node->size * 0.5;
	return p;
}

inline Vector3 get_center_right_bottom(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size;
	p.z += node->size * 0.5;
	return p;
}

inline Vector3 get_center_back_left(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.y += node->size * 0.5;
	return p;
}

inline Vector3 get_center_front_left(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.y += node->size * 0.5;
	p.z += node->size;
	return p;
}

inline Vector3 get_center_back_right(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size;
	p.y += node->size * 0.5;
	return p;
}

inline Vector3 get_center_front_right(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size;
	p.y += node->size * 0.5;
	p.z += node->size;
	return p;
}

inline Vector3 get_corner1(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size;
	return p;
}

inline Vector3 get_corner2(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size;
	p.z += node->size;
	return p;
}

inline Vector3 get_corner3(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.z += node->size;
	return p;
}

inline Vector3 get_corner4(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.y += node->size;
	return p;
}

inline Vector3 get_corner5(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size;
	p.y += node->size;
	return p;
}

inline Vector3 get_corner6(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.x += node->size;
	p.y += node->size;
	p.z += node->size;
	return p;
}

inline Vector3 get_corner7(const OctreeNode *node) {
	Vector3 p = node->origin.to_vec3();
	p.y += node->size;
	p.z += node->size;
	return p;
}

class DualGridGenerator {
public:
	DualGridGenerator(DualGrid &grid, int octree_root_size) :
			_grid(grid),
			_octree_root_size(octree_root_size) {}

	void node_proc(OctreeNode *node);

private:
	DualGrid &_grid;
	int _octree_root_size;

	void create_border_cells(
			const OctreeNode *n0,
			const OctreeNode *n1,
			const OctreeNode *n2,
			const OctreeNode *n3,
			const OctreeNode *n4,
			const OctreeNode *n5,
			const OctreeNode *n6,
			const OctreeNode *n7);

	void vert_proc(OctreeNode *n0, OctreeNode *n1, OctreeNode *n2, OctreeNode *n3, OctreeNode *n4, OctreeNode *n5, OctreeNode *n6, OctreeNode *n7);

	void edge_proc_x(OctreeNode *n0, OctreeNode *n1, OctreeNode *n2, OctreeNode *n3);
	void edge_proc_y(OctreeNode *n0, OctreeNode *n1, OctreeNode *n2, OctreeNode *n3);
	void edge_proc_z(OctreeNode *n0, OctreeNode *n1, OctreeNode *n2, OctreeNode *n3);

	void face_proc_xy(OctreeNode *n0, OctreeNode *n1);
	void face_proc_zy(OctreeNode *n0, OctreeNode *n1);
	void face_proc_xz(OctreeNode *n0, OctreeNode *n1);
};

inline void add_cell(DualGrid &grid,
		const Vector3 c0,
		const Vector3 c1,
		const Vector3 c2,
		const Vector3 c3,
		const Vector3 c4,
		const Vector3 c5,
		const Vector3 c6,
		const Vector3 c7) {

	DualCell cell;
	cell.corners[0] = c0;
	cell.corners[1] = c1;
	cell.corners[2] = c2;
	cell.corners[3] = c3;
	cell.corners[4] = c4;
	cell.corners[5] = c5;
	cell.corners[6] = c6;
	cell.corners[7] = c7;
	cell.has_values = false;
	grid.cells.push_back(cell);
}

void DualGridGenerator::create_border_cells(
		const OctreeNode *n0,
		const OctreeNode *n1,
		const OctreeNode *n2,
		const OctreeNode *n3,
		const OctreeNode *n4,
		const OctreeNode *n5,
		const OctreeNode *n6,
		const OctreeNode *n7) {

	DualGrid &grid = _grid;

	// Most boring function ever

	if (is_border_back(n0) && is_border_back(n1) && is_border_back(n4) && is_border_back(n5)) {

		add_cell(grid,
				get_center_back(n0), get_center_back(n1), get_center(n1), get_center(n0),
				get_center_back(n4), get_center_back(n5), get_center(n5), get_center(n4));

		// Generate back edge border cells
		if (is_border_top(n4, _octree_root_size) && is_border_top(n5, _octree_root_size)) {

			add_cell(grid,
					get_center_back(n4), get_center_back(n5), get_center(n5), get_center(n4),
					get_center_back_top(n4), get_center_back_top(n5), get_center_top(n5), get_center_top(n4));

			// Generate back top corner cells
			if (is_border_left(n4)) {
				add_cell(grid,
						get_center_back_left(n4), get_center_back(n4), get_center(n4), get_center_left(n4),
						get_corner4(n4), get_center_back_top(n4), get_center_top(n4), get_center_left_top(n4));
			}

			if (is_border_right(n4, _octree_root_size)) {
				add_cell(grid,
						get_center_back(n5), get_center_back_right(n5), get_center_right(n5), get_center(n5),
						get_center_back_top(n5), get_corner5(n5), get_center_right_top(n5), get_center_top(n5));
			}
		}

		if (is_border_bottom(n0) && is_border_bottom(n1)) {

			add_cell(grid,
					get_center_back_bottom(n0), get_center_back_bottom(n1), get_center_bottom(n1), get_center_bottom(n0),
					get_center_back(n0), get_center_back(n1), get_center(n1), get_center(n0));

			// Generate back bottom corner cells
			if (is_border_left(n0)) {
				add_cell(grid, n0->origin.to_vec3(), get_center_back_bottom(n0), get_center_bottom(n0), get_center_left_bottom(n0),
						get_center_back_left(n0), get_center_back(n0), get_center(n0), get_center_left(n0));
			}

			if (is_border_right(n1, _octree_root_size)) {
				add_cell(grid, get_center_back_bottom(n1), get_corner1(n1), get_center_right_bottom(n1), get_center_bottom(n1),
						get_center_back(n1), get_center_back_right(n1), get_center_right(n1), get_center(n1));
			}
		}
	}

	if (is_border_front(n2, _octree_root_size) &&
			is_border_front(n3, _octree_root_size) &&
			is_border_front(n6, _octree_root_size) &&
			is_border_front(n7, _octree_root_size)) {

		add_cell(grid,
				get_center(n3), get_center(n2), get_center_front(n2), get_center_front(n3),
				get_center(n7), get_center(n6), get_center_front(n6), get_center_front(n7));

		// Generate front edge border cells
		if (is_border_top(n6, _octree_root_size) && is_border_top(n7, _octree_root_size)) {

			add_cell(grid,
					get_center(n7), get_center(n6), get_center_front(n6), get_center_front(n7),
					get_center_top(n7), get_center_top(n6), get_center_front_top(n6), get_center_front_top(n7));

			// Generate back bottom corner cells
			if (is_border_left(n7)) {
				add_cell(grid,
						get_center_left(n7), get_center(n7), get_center_front(n7), get_center_front_left(n7),
						get_center_left_top(n7), get_center_top(n7), get_center_front_top(n7), get_corner7(n7));
			}

			if (is_border_right(n6, _octree_root_size)) {
				add_cell(grid,
						get_center(n6), get_center_right(n6), get_center_front_right(n6), get_center_front(n6),
						get_center_top(n6), get_center_right_top(n6), get_corner6(n6), get_center_front_top(n6));
			}
		}

		if (is_border_bottom(n3) && is_border_bottom(n2)) {

			add_cell(grid,
					get_center_bottom(n3), get_center_bottom(n2), get_center_front_bottom(n2), get_center_front_bottom(n3),
					get_center(n3), get_center(n2), get_center_front(n2), get_center_front(n3));

			// Generate back bottom corner cells
			if (is_border_left(n3)) {
				add_cell(grid,
						get_center_left_bottom(n3), get_center_bottom(n3), get_center_front_bottom(n3), get_corner3(n3),
						get_center_left(n3), get_center(n3), get_center_front(n3), get_center_front_left(n3));
			}
			if (is_border_right(n2, _octree_root_size)) {
				add_cell(grid, get_center_bottom(n2), get_center_right_bottom(n2), get_corner2(n2), get_center_front_bottom(n2),
						get_center(n2), get_center_right(n2), get_center_front_right(n2), get_center_front(n2));
			}
		}
	}

	if (is_border_left(n0) && is_border_left(n3) && is_border_left(n4) && is_border_left(n7)) {

		add_cell(grid,
				get_center_left(n0), get_center(n0), get_center(n3), get_center_left(n3),
				get_center_left(n4), get_center(n4), get_center(n7), get_center_left(n7));

		// Generate left edge border cells
		if (is_border_top(n4, _octree_root_size) && is_border_top(n7, _octree_root_size)) {
			add_cell(grid,
					get_center_left(n4), get_center(n4), get_center(n7), get_center_left(n7),
					get_center_left_top(n4), get_center_top(n4), get_center_top(n7), get_center_left_top(n7));
		}

		if (is_border_bottom(n0) && is_border_bottom(n3)) {
			add_cell(grid,
					get_center_left_bottom(n0), get_center_bottom(n0), get_center_bottom(n3), get_center_left_bottom(n3),
					get_center_left(n0), get_center(n0), get_center(n3), get_center_left(n3));
		}

		if (is_border_back(n0) && is_border_back(n4)) {
			add_cell(grid,
					get_center_back_left(n0), get_center_back(n0), get_center(n0), get_center_left(n0),
					get_center_back_left(n4), get_center_back(n4), get_center(n4), get_center_left(n4));
		}

		if (is_border_front(n3, _octree_root_size) && is_border_front(n7, _octree_root_size)) {
			add_cell(grid,
					get_center_left(n3), get_center(n3), get_center_front(n3), get_center_front_left(n3),
					get_center_left(n7), get_center(n7), get_center_front(n7), get_center_front_left(n7));
		}
	}

	if (is_border_right(n1, _octree_root_size) &&
			is_border_right(n2, _octree_root_size) &&
			is_border_right(n5, _octree_root_size) &&
			is_border_right(n6, _octree_root_size)) {

		add_cell(grid,
				get_center(n1), get_center_right(n1), get_center_right(n2), get_center(n2),
				get_center(n5), get_center_right(n5), get_center_right(n6), get_center(n6));

		// Generate right edge border cells
		if (is_border_top(n5, _octree_root_size) && is_border_top(n6, _octree_root_size)) {
			add_cell(grid,
					get_center(n5), get_center_right(n5), get_center_right(n6), get_center(n6),
					get_center_top(n5), get_center_right_top(n5), get_center_right_top(n6), get_center_top(n6));
		}

		if (is_border_bottom(n1) && is_border_bottom(n2)) {
			add_cell(grid,
					get_center_bottom(n1), get_center_right_bottom(n1), get_center_right_bottom(n2), get_center_bottom(n2),
					get_center(n1), get_center_right(n1), get_center_right(n2), get_center(n2));
		}

		if (is_border_back(n1) && is_border_back(n5)) {
			add_cell(grid,
					get_center_back(n1), get_center_back_right(n1), get_center_right(n1), get_center(n1),
					get_center_back(n5), get_center_back_right(n5), get_center_right(n5), get_center(n5));
		}

		if (is_border_front(n2, _octree_root_size) && is_border_front(n6, _octree_root_size)) {
			add_cell(grid,
					get_center(n2), get_center_right(n2), get_center_front_right(n2), get_center_front(n2),
					get_center(n6), get_center_right(n6), get_center_front_right(n6), get_center_front(n6));
		}
	}

	if (is_border_top(n4, _octree_root_size) &&
			is_border_top(n5, _octree_root_size) &&
			is_border_top(n6, _octree_root_size) &&
			is_border_top(n7, _octree_root_size)) {

		add_cell(grid,
				get_center(n4), get_center(n5), get_center(n6), get_center(n7),
				get_center_top(n4), get_center_top(n5), get_center_top(n6), get_center_top(n7));
	}

	if (is_border_bottom(n0) && is_border_bottom(n1) && is_border_bottom(n2) && is_border_bottom(n3)) {
		add_cell(grid,
				get_center_bottom(n0), get_center_bottom(n1), get_center_bottom(n2), get_center_bottom(n3),
				get_center(n0), get_center(n1), get_center(n2), get_center(n3));
	}
}

inline bool is_surface_near(OctreeNode *node) {
	if (node->center_value.value == 0) {
		return true;
	}
	return Math::abs(node->center_value.value) < node->size * SQRT3 * NEAR_SURFACE_FACTOR;
}

void DualGridGenerator::vert_proc(
		OctreeNode *n0,
		OctreeNode *n1,
		OctreeNode *n2,
		OctreeNode *n3,
		OctreeNode *n4,
		OctreeNode *n5,
		OctreeNode *n6,
		OctreeNode *n7) {

	const bool n0_has_children = n0->has_children();
	const bool n1_has_children = n1->has_children();
	const bool n2_has_children = n2->has_children();
	const bool n3_has_children = n3->has_children();
	const bool n4_has_children = n4->has_children();
	const bool n5_has_children = n5->has_children();
	const bool n6_has_children = n6->has_children();
	const bool n7_has_children = n7->has_children();

	if (
			n0_has_children || n1_has_children || n2_has_children || n3_has_children ||
			n4_has_children || n5_has_children || n6_has_children || n7_has_children) {

		OctreeNode *c0 = n0_has_children ? n0->children[6] : n0;
		OctreeNode *c1 = n1_has_children ? n1->children[7] : n1;
		OctreeNode *c2 = n2_has_children ? n2->children[4] : n2;
		OctreeNode *c3 = n3_has_children ? n3->children[5] : n3;
		OctreeNode *c4 = n4_has_children ? n4->children[2] : n4;
		OctreeNode *c5 = n5_has_children ? n5->children[3] : n5;
		OctreeNode *c6 = n6_has_children ? n6->children[0] : n6;
		OctreeNode *c7 = n7_has_children ? n7->children[1] : n7;

		vert_proc(c0, c1, c2, c3, c4, c5, c6, c7);

	} else {

		if (!(
					is_surface_near(n0) ||
					is_surface_near(n1) ||
					is_surface_near(n2) ||
					is_surface_near(n3) ||
					is_surface_near(n4) ||
					is_surface_near(n5) ||
					is_surface_near(n6) ||
					is_surface_near(n7))) {
			return;
		}

		DualCell cell;
		cell.set_corner(0, get_center(n0), n0->center_value);
		cell.set_corner(1, get_center(n1), n1->center_value);
		cell.set_corner(2, get_center(n2), n2->center_value);
		cell.set_corner(3, get_center(n3), n3->center_value);
		cell.set_corner(4, get_center(n4), n4->center_value);
		cell.set_corner(5, get_center(n5), n5->center_value);
		cell.set_corner(6, get_center(n6), n6->center_value);
		cell.set_corner(7, get_center(n7), n7->center_value);
		cell.has_values = true;
		_grid.cells.push_back(cell);

		create_border_cells(n0, n1, n2, n3, n4, n5, n6, n7);
	}
}

void DualGridGenerator::edge_proc_x(OctreeNode *n0, OctreeNode *n1, OctreeNode *n2, OctreeNode *n3) {

	const bool n0_has_children = n0->has_children();
	const bool n1_has_children = n1->has_children();
	const bool n2_has_children = n2->has_children();
	const bool n3_has_children = n3->has_children();

	if (!(n0_has_children || n1_has_children || n2_has_children || n3_has_children)) {
		return;
	}

	OctreeNode *c0 = n0_has_children ? n0->children[7] : n0;
	OctreeNode *c1 = n0_has_children ? n0->children[6] : n0;
	OctreeNode *c2 = n1_has_children ? n1->children[5] : n1;
	OctreeNode *c3 = n1_has_children ? n1->children[4] : n1;
	OctreeNode *c4 = n3_has_children ? n3->children[3] : n3;
	OctreeNode *c5 = n3_has_children ? n3->children[2] : n3;
	OctreeNode *c6 = n2_has_children ? n2->children[1] : n2;
	OctreeNode *c7 = n2_has_children ? n2->children[0] : n2;

	edge_proc_x(c0, c3, c7, c4);
	edge_proc_x(c1, c2, c6, c5);

	vert_proc(c0, c1, c2, c3, c4, c5, c6, c7);
}

void DualGridGenerator::edge_proc_y(OctreeNode *n0, OctreeNode *n1, OctreeNode *n2, OctreeNode *n3) {

	const bool n0_has_children = n0->has_children();
	const bool n1_has_children = n1->has_children();
	const bool n2_has_children = n2->has_children();
	const bool n3_has_children = n3->has_children();

	if (!(n0_has_children || n1_has_children || n2_has_children || n3_has_children)) {
		return;
	}

	OctreeNode *c0 = n0_has_children ? n0->children[2] : n0;
	OctreeNode *c1 = n1_has_children ? n1->children[3] : n1;
	OctreeNode *c2 = n2_has_children ? n2->children[0] : n2;
	OctreeNode *c3 = n3_has_children ? n3->children[1] : n3;
	OctreeNode *c4 = n0_has_children ? n0->children[6] : n0;
	OctreeNode *c5 = n1_has_children ? n1->children[7] : n1;
	OctreeNode *c6 = n2_has_children ? n2->children[4] : n2;
	OctreeNode *c7 = n3_has_children ? n3->children[5] : n3;

	edge_proc_y(c0, c1, c2, c3);
	edge_proc_y(c4, c5, c6, c7);

	vert_proc(c0, c1, c2, c3, c4, c5, c6, c7);
}

void DualGridGenerator::edge_proc_z(OctreeNode *n0, OctreeNode *n1, OctreeNode *n2, OctreeNode *n3) {

	const bool n0_has_children = n0->has_children();
	const bool n1_has_children = n1->has_children();
	const bool n2_has_children = n2->has_children();
	const bool n3_has_children = n3->has_children();

	if (!(n0_has_children || n1_has_children || n2_has_children || n3_has_children)) {
		return;
	}

	OctreeNode *c0 = n3_has_children ? n3->children[5] : n3;
	OctreeNode *c1 = n2_has_children ? n2->children[4] : n2;
	OctreeNode *c2 = n2_has_children ? n2->children[7] : n2;
	OctreeNode *c3 = n3_has_children ? n3->children[6] : n3;
	OctreeNode *c4 = n0_has_children ? n0->children[1] : n0;
	OctreeNode *c5 = n1_has_children ? n1->children[0] : n1;
	OctreeNode *c6 = n1_has_children ? n1->children[3] : n1;
	OctreeNode *c7 = n0_has_children ? n0->children[2] : n0;

	edge_proc_z(c7, c6, c2, c3);
	edge_proc_z(c4, c5, c1, c0);

	vert_proc(c0, c1, c2, c3, c4, c5, c6, c7);
}

void DualGridGenerator::face_proc_xy(OctreeNode *n0, OctreeNode *n1) {

	const bool n0_has_children = n0->has_children();
	const bool n1_has_children = n1->has_children();

	if (!(n0_has_children || n1_has_children)) {
		return;
	}

	OctreeNode *c0 = n0_has_children ? n0->children[3] : n0;
	OctreeNode *c1 = n0_has_children ? n0->children[2] : n0;
	OctreeNode *c2 = n1_has_children ? n1->children[1] : n1;
	OctreeNode *c3 = n1_has_children ? n1->children[0] : n1;
	OctreeNode *c4 = n0_has_children ? n0->children[7] : n0;
	OctreeNode *c5 = n0_has_children ? n0->children[6] : n0;
	OctreeNode *c6 = n1_has_children ? n1->children[5] : n1;
	OctreeNode *c7 = n1_has_children ? n1->children[4] : n1;

	face_proc_xy(c0, c3);
	face_proc_xy(c1, c2);
	face_proc_xy(c4, c7);
	face_proc_xy(c5, c6);

	edge_proc_x(c0, c3, c7, c4);
	edge_proc_x(c1, c2, c6, c5);

	edge_proc_y(c0, c1, c2, c3);
	edge_proc_y(c4, c5, c6, c7);

	vert_proc(c0, c1, c2, c3, c4, c5, c6, c7);
}

void DualGridGenerator::face_proc_zy(OctreeNode *n0, OctreeNode *n1) {

	const bool n0_has_children = n0->has_children();
	const bool n1_has_children = n1->has_children();

	if (!(n0_has_children || n1_has_children)) {
		return;
	}

	OctreeNode *c0 = n0_has_children ? n0->children[1] : n0;
	OctreeNode *c1 = n1_has_children ? n1->children[0] : n1;
	OctreeNode *c2 = n1_has_children ? n1->children[3] : n1;
	OctreeNode *c3 = n0_has_children ? n0->children[2] : n0;
	OctreeNode *c4 = n0_has_children ? n0->children[5] : n0;
	OctreeNode *c5 = n1_has_children ? n1->children[4] : n1;
	OctreeNode *c6 = n1_has_children ? n1->children[7] : n1;
	OctreeNode *c7 = n0_has_children ? n0->children[6] : n0;

	face_proc_zy(c0, c1);
	face_proc_zy(c3, c2);
	face_proc_zy(c4, c5);
	face_proc_zy(c7, c6);

	edge_proc_y(c0, c1, c2, c3);
	edge_proc_y(c4, c5, c6, c7);
	edge_proc_z(c7, c6, c2, c3);
	edge_proc_z(c4, c5, c1, c0);

	vert_proc(c0, c1, c2, c3, c4, c5, c6, c7);
}

void DualGridGenerator::face_proc_xz(OctreeNode *n0, OctreeNode *n1) {

	const bool n0_has_children = n0->has_children();
	const bool n1_has_children = n1->has_children();

	if (!(n0_has_children || n1_has_children)) {
		return;
	}

	OctreeNode *c0 = n1_has_children ? n1->children[4] : n1;
	OctreeNode *c1 = n1_has_children ? n1->children[5] : n1;
	OctreeNode *c2 = n1_has_children ? n1->children[6] : n1;
	OctreeNode *c3 = n1_has_children ? n1->children[7] : n1;
	OctreeNode *c4 = n0_has_children ? n0->children[0] : n0;
	OctreeNode *c5 = n0_has_children ? n0->children[1] : n0;
	OctreeNode *c6 = n0_has_children ? n0->children[2] : n0;
	OctreeNode *c7 = n0_has_children ? n0->children[3] : n0;

	face_proc_xz(c4, c0);
	face_proc_xz(c5, c1);
	face_proc_xz(c7, c3);
	face_proc_xz(c6, c2);

	edge_proc_x(c0, c3, c7, c4);
	edge_proc_x(c1, c2, c6, c5);
	edge_proc_z(c7, c6, c2, c3);
	edge_proc_z(c4, c5, c1, c0);

	vert_proc(c0, c1, c2, c3, c4, c5, c6, c7);
}

void DualGridGenerator::node_proc(OctreeNode *node) {

	if (!node->has_children()) {
		return;
	}

	OctreeNode **children = node->children;

	for (int i = 0; i < 8; ++i) {
		node_proc(children[i]);
	}

	face_proc_xy(children[0], children[3]);
	face_proc_xy(children[1], children[2]);
	face_proc_xy(children[4], children[7]);
	face_proc_xy(children[5], children[6]);

	face_proc_zy(children[0], children[1]);
	face_proc_zy(children[3], children[2]);
	face_proc_zy(children[4], children[5]);
	face_proc_zy(children[7], children[6]);

	face_proc_xz(children[4], children[0]);
	face_proc_xz(children[5], children[1]);
	face_proc_xz(children[7], children[3]);
	face_proc_xz(children[6], children[2]);

	edge_proc_x(children[0], children[3], children[7], children[4]);
	edge_proc_x(children[1], children[2], children[6], children[5]);

	edge_proc_y(children[0], children[1], children[2], children[3]);
	edge_proc_y(children[4], children[5], children[6], children[7]);

	edge_proc_z(children[7], children[6], children[2], children[3]);
	edge_proc_z(children[4], children[5], children[1], children[0]);

	vert_proc(children[0], children[1], children[2], children[3], children[4], children[5], children[6], children[7]);
}

inline Vector3 interpolate(const Vector3 &v0, const Vector3 &v1, const HermiteValue &val0, const HermiteValue &val1, Vector3 &out_normal) {

	if (Math::abs(val0.value - SURFACE_ISO_LEVEL) <= FLT_EPSILON) {
		out_normal = val0.gradient;
		return v0;
	}

	if (Math::abs(val1.value - SURFACE_ISO_LEVEL) <= FLT_EPSILON) {
		out_normal = val1.gradient;
		return v1;
	}

	if (Math::abs(val1.value - val0.value) <= FLT_EPSILON) {
		out_normal = val0.gradient;
		return v0;
	}

	float mu = (SURFACE_ISO_LEVEL - val0.value) / (val1.value - val0.value);
	out_normal = val0.gradient + mu * (val1.gradient - val0.gradient);
	out_normal.normalize();

	return v0 + mu * (v1 - v0);
}

void polygonize_cell_marching_cubes(const Vector3 *corners, const HermiteValue *values, MeshBuilder &mesh_builder) {

	unsigned char case_index = 0;

	for (int i = 0; i < 8; ++i) {
		if (values[i].value >= SURFACE_ISO_LEVEL) {
			case_index |= 1 << i;
		}
	}

	int edge = MarchingCubes::mc_edges[case_index];

	if (!edge) {
		// Nothing intersects
		return;
	}

	// Find the intersection vertices
	Vector3 intersection_points[12];
	Vector3 intersection_normals[12];
	if (edge & 1) {
		intersection_points[0] = interpolate(corners[0], corners[1], values[0], values[1], intersection_normals[0]);
	}
	if (edge & 2) {
		intersection_points[1] = interpolate(corners[1], corners[2], values[1], values[2], intersection_normals[1]);
	}
	if (edge & 4) {
		intersection_points[2] = interpolate(corners[2], corners[3], values[2], values[3], intersection_normals[2]);
	}
	if (edge & 8) {
		intersection_points[3] = interpolate(corners[3], corners[0], values[3], values[0], intersection_normals[3]);
	}
	if (edge & 16) {
		intersection_points[4] = interpolate(corners[4], corners[5], values[4], values[5], intersection_normals[4]);
	}
	if (edge & 32) {
		intersection_points[5] = interpolate(corners[5], corners[6], values[5], values[6], intersection_normals[5]);
	}
	if (edge & 64) {
		intersection_points[6] = interpolate(corners[6], corners[7], values[6], values[7], intersection_normals[6]);
	}
	if (edge & 128) {
		intersection_points[7] = interpolate(corners[7], corners[4], values[7], values[4], intersection_normals[7]);
	}
	if (edge & 256) {
		intersection_points[8] = interpolate(corners[0], corners[4], values[0], values[4], intersection_normals[8]);
	}
	if (edge & 512) {
		intersection_points[9] = interpolate(corners[1], corners[5], values[1], values[5], intersection_normals[9]);
	}
	if (edge & 1024) {
		intersection_points[10] = interpolate(corners[2], corners[6], values[2], values[6], intersection_normals[10]);
	}
	if (edge & 2048) {
		intersection_points[11] = interpolate(corners[3], corners[7], values[3], values[7], intersection_normals[11]);
	}

	// Create the triangles according to the table.
	for (int i = 0; MarchingCubes::mc_triangles[case_index][i] != -1; i += 3) {

		mesh_builder.add_vertex(
				intersection_points[MarchingCubes::mc_triangles[case_index][i]],
				intersection_normals[MarchingCubes::mc_triangles[case_index][i]]);

		mesh_builder.add_vertex(
				intersection_points[MarchingCubes::mc_triangles[case_index][i + 1]],
				intersection_normals[MarchingCubes::mc_triangles[case_index][i + 1]]);

		mesh_builder.add_vertex(
				intersection_points[MarchingCubes::mc_triangles[case_index][i + 2]],
				intersection_normals[MarchingCubes::mc_triangles[case_index][i + 2]]);
	}

	return;
}

void polygonize_dual_cell(const DualCell &cell, const VoxelAccess &voxels, MeshBuilder &mesh_builder) {

	const Vector3 *corners = cell.corners;
	HermiteValue values[8];

	if (cell.has_values) {
		memcpy(values, cell.values, 8 * sizeof(HermiteValue));
	} else {
		for (int i = 0; i < 8; ++i) {
			values[i] = voxels.get_interpolated_hermite_value(corners[i]);
		}
	}

	polygonize_cell_marching_cubes(corners, values, mesh_builder);
}

inline void polygonize_dual_grid(const DualGrid &grid, const VoxelAccess &voxels, MeshBuilder &mesh_builder) {

	for (int i = 0; i < grid.cells.size(); ++i) {
		polygonize_dual_cell(grid.cells[i], voxels, mesh_builder);
	}
}

void polygonize_volume_directly(const VoxelBuffer &voxels, Vector3i min, Vector3i size, MeshBuilder &mesh_builder) {

	Vector3 corners[8];
	HermiteValue values[8];

	const Vector3i max = min + size;
	const Vector3 minf = min.to_vec3();

	for (int z = min.z; z < max.z; ++z) {
		for (int x = min.x; x < max.x; ++x) {
			for (int y = min.y; y < max.y; ++y) {

				values[0] = get_hermite_value(voxels, x, y, z);
				values[1] = get_hermite_value(voxels, x + 1, y, z);
				values[2] = get_hermite_value(voxels, x + 1, y, z + 1);
				values[3] = get_hermite_value(voxels, x, y, z + 1);
				values[4] = get_hermite_value(voxels, x, y + 1, z);
				values[5] = get_hermite_value(voxels, x + 1, y + 1, z);
				values[6] = get_hermite_value(voxels, x + 1, y + 1, z + 1);
				values[7] = get_hermite_value(voxels, x, y + 1, z + 1);

				corners[0] = Vector3(x, y, z);
				corners[1] = Vector3(x + 1, y, z);
				corners[2] = Vector3(x + 1, y, z + 1);
				corners[3] = Vector3(x, y, z + 1);
				corners[4] = Vector3(x, y + 1, z);
				corners[5] = Vector3(x + 1, y + 1, z);
				corners[6] = Vector3(x + 1, y + 1, z + 1);
				corners[7] = Vector3(x, y + 1, z + 1);

				for (int i = 0; i < 8; ++i) {
					corners[i] -= minf;
				}

				polygonize_cell_marching_cubes(corners, values, mesh_builder);
			}
		}
	}
}

} // namespace dmc

#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) {
	_mesh_mode = mode;
}

VoxelMesherDMC::MeshMode VoxelMesherDMC::get_mesh_mode() const {
	return _mesh_mode;
}

void VoxelMesherDMC::set_octree_mode(OctreeMode mode) {
	_octree_mode = mode;
}

VoxelMesherDMC::OctreeMode VoxelMesherDMC::get_octree_mode() const {
	return _octree_mode;
}

void VoxelMesherDMC::set_geometric_error(real_t geometric_error) {
	_geometric_error = geometric_error;
}

float VoxelMesherDMC::get_geometric_error() const {
	return _geometric_error;
}

void VoxelMesherDMC::build(VoxelMesher::Output &output, const VoxelBuffer &voxels, int padding) {

	// Requirements:
	// - Voxel data must be padded
	// - Gradients must be precalculated
	// - The non-padded area size is cubic and power of two

	_stats = { 0 };

	if (voxels.is_uniform(VoxelBuffer::CHANNEL_ISOLEVEL)) {
		// That won't produce any polygon
		return;
	}

	ERR_FAIL_COND(padding < MINIMUM_PADDING);

	const Vector3i buffer_size = voxels.get_size();
	// Taking previous power of two because the algorithm uses an integer cubic octree, and data should be padded
	int chunk_size = previous_power_of_2(MIN(MIN(buffer_size.x, buffer_size.y), buffer_size.z));

	ERR_FAIL_COND(voxels.get_size().x < chunk_size + padding * 2);
	ERR_FAIL_COND(voxels.get_size().y < chunk_size + padding * 2);
	ERR_FAIL_COND(voxels.get_size().z < chunk_size + padding * 2);

	// Construct an intermediate to handle padding transparently
	dmc::VoxelAccess voxels_access(voxels, Vector3i(padding));

	real_t time_before = OS::get_singleton()->get_ticks_usec();

	// In an ideal world, a tiny sphere placed in the middle of an empty SDF volume will
	// cause corners data to change so that they indicate distance to it.
	// That means we could build our meshing octree top-down efficiently because corners of the volume will tell if the
	// distance to any surface is varying.
	//
	// For large terrains, 8-bit isolevels with quantification of -1..1 could be enough to represent surfaces.
	// It compresses well, and we don't need to propagate distance changes to the whole volume as we edit it.
	// Finally, it's easy to find uniform locations, they will be filled with 0 or 255, and discarded,
	// or possibly stored in a data octree already.
	//
	// Problem:
	// If you try building the meshing octree top-down in that case, it could see corners all have value of 1,
	// and will skip everything, assuming the volume contains nothing.
	// Building the octree bottom-up ensures to always catch voxels of any size, but will be a bit slower
	// because all voxels are queried.
	//
	// TODO This option might disappear once I find a good enough solution
	dmc::OctreeNode *root = nullptr;
	if (_octree_mode == OCTREE_BOTTOM_UP) {

		dmc::OctreeBuilderBottomUp octree_builder(voxels_access, _geometric_error, _octree_node_pool);
		root = octree_builder.build(Vector3i(), chunk_size);

	} else if (_octree_mode == OCTREE_TOP_DOWN) {

		dmc::OctreeBuilderTopDown octree_builder(voxels_access, _geometric_error, _octree_node_pool);
		root = octree_builder.build(Vector3i(), chunk_size);
	}

	_stats.octree_build_time = OS::get_singleton()->get_ticks_usec() - time_before;

	Array surface;

	if (root != nullptr) {

		if (_mesh_mode == MESH_DEBUG_OCTREE) {
			surface = dmc::generate_debug_octree_mesh(root);

		} else {

			time_before = OS::get_singleton()->get_ticks_usec();

			dmc::DualGridGenerator dual_grid_generator(_dual_grid, root->size);
			dual_grid_generator.node_proc(root);
			// TODO Handle non-subdivided octree

			_stats.dualgrid_derivation_time = OS::get_singleton()->get_ticks_usec() - time_before;

			if (_mesh_mode == MESH_DEBUG_DUAL_GRID) {
				surface = dmc::generate_debug_dual_grid_mesh(_dual_grid);

			} else {

				time_before = OS::get_singleton()->get_ticks_usec();
				dmc::polygonize_dual_grid(_dual_grid, voxels_access, _mesh_builder);
				_stats.meshing_time = OS::get_singleton()->get_ticks_usec() - time_before;
			}

			_dual_grid.cells.clear();
		}

		root->recycle(_octree_node_pool);

	} else if (_octree_mode == OCTREE_NONE) {

		// We throw away adaptivity for meshing speed.
		// This is essentially regular marching cubes.

		time_before = OS::get_singleton()->get_ticks_usec();
		dmc::polygonize_volume_directly(voxels, Vector3i(padding), Vector3i(chunk_size), _mesh_builder);
		_stats.meshing_time = OS::get_singleton()->get_ticks_usec() - time_before;
	}

	if (surface.empty()) {
		time_before = OS::get_singleton()->get_ticks_usec();
		surface = _mesh_builder.commit(_mesh_mode == MESH_WIREFRAME);
		_stats.commit_time = OS::get_singleton()->get_ticks_usec() - time_before;
	}

	// TODO Marching squares skirts

	// surfaces[material][array_type], for now single material
	output.surfaces.push_back(surface);

	if (_mesh_mode == MESH_NORMAL) {
		output.primitive_type = Mesh::PRIMITIVE_TRIANGLES;
	} else {
		output.primitive_type = Mesh::PRIMITIVE_LINES;
	}
}

int VoxelMesherDMC::get_minimum_padding() const {
	return MINIMUM_PADDING;
}

Dictionary VoxelMesherDMC::get_stats() const {
	Dictionary d;
	d["octree_build_time"] = _stats.octree_build_time;
	d["dualgrid_derivation_time"] = _stats.dualgrid_derivation_time;
	d["meshing_time"] = _stats.meshing_time;
	d["commit_time"] = _stats.commit_time;
	return d;
}

void VoxelMesherDMC::_bind_methods() {

	ClassDB::bind_method(D_METHOD("set_mesh_mode", "mode"), &VoxelMesherDMC::set_mesh_mode);
	ClassDB::bind_method(D_METHOD("get_mesh_mode"), &VoxelMesherDMC::get_mesh_mode);

	ClassDB::bind_method(D_METHOD("set_octree_mode", "mode"), &VoxelMesherDMC::set_octree_mode);
	ClassDB::bind_method(D_METHOD("get_octree_mode"), &VoxelMesherDMC::get_octree_mode);

	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("get_stats"), &VoxelMesherDMC::get_stats);

	BIND_ENUM_CONSTANT(MESH_NORMAL);
	BIND_ENUM_CONSTANT(MESH_WIREFRAME);
	BIND_ENUM_CONSTANT(MESH_DEBUG_OCTREE);
	BIND_ENUM_CONSTANT(MESH_DEBUG_DUAL_GRID);

	BIND_ENUM_CONSTANT(OCTREE_BOTTOM_UP);
	BIND_ENUM_CONSTANT(OCTREE_TOP_DOWN);
	BIND_ENUM_CONSTANT(OCTREE_NONE);
}