ET/Unity/Assets/Plugins/AstarPathfindingProject/Generators/Utilities/Voxels/VoxelPolygonClipper.cs

namespace Pathfinding.Voxels {
	/// <summary>Utility for clipping polygons</summary>
	internal struct VoxelPolygonClipper {
		public float[] x;
		public float[] y;
		public float[] z;
		public int n;

		public VoxelPolygonClipper (int capacity) {
			x = new float[capacity];
			y = new float[capacity];
			z = new float[capacity];
			n = 0;
		}

		public UnityEngine.Vector3 this[int i] {
			set {
				x[i] = value.x;
				y[i] = value.y;
				z[i] = value.z;
			}
		}

		/// <summary>
		/// Clips a polygon against an axis aligned half plane.
		/// The polygons stored in this object are clipped against the half plane at x = -offset.
		/// </summary>
		/// <param name="result">Ouput vertices</param>
		/// <param name="multi">Scale factor for the input vertices. Should be +1 or -1. If -1 the negative half plane is kept.</param>
		/// <param name="offset">Offset to move the input vertices with before cutting</param>
		public void ClipPolygonAlongX (ref VoxelPolygonClipper result, float multi, float offset) {
			// Number of resulting vertices
			int m = 0;
			bool prev, curr;

			float dj = multi*x[(n-1)]+offset;

			for (int i = 0, j = n-1; i < n; j = i, i++) {
				float di = multi*x[i]+offset;
				prev = dj >= 0;
				curr = di >= 0;

				if (prev != curr) {
					float s = dj / (dj - di);
					result.x[m] = x[j] + (x[i]-x[j])*s;
					result.y[m] = y[j] + (y[i]-y[j])*s;
					result.z[m] = z[j] + (z[i]-z[j])*s;
					m++;
				}

				if (curr) {
					result.x[m] = x[i];
					result.y[m] = y[i];
					result.z[m] = z[i];
					m++;
				}

				dj = di;
			}

			result.n = m;
		}

		/// <summary>
		/// Clips a polygon against an axis aligned half plane.
		/// The polygons stored in this object are clipped against the half plane at z = -offset.
		/// </summary>
		/// <param name="result">Ouput vertices. Only the Y and Z coordinates are calculated. The X coordinates are undefined.</param>
		/// <param name="multi">Scale factor for the input vertices. Should be +1 or -1. If -1 the negative half plane is kept.</param>
		/// <param name="offset">Offset to move the input vertices with before cutting</param>
		public void ClipPolygonAlongZWithYZ (ref VoxelPolygonClipper result, float multi, float offset) {
			// Number of resulting vertices
			int m = 0;
			bool prev, curr;

			float dj = multi*z[(n-1)]+offset;

			for (int i = 0, j = n-1; i < n; j = i, i++) {
				float di = multi*z[i]+offset;
				prev = dj >= 0;
				curr = di >= 0;

				if (prev != curr) {
					float s = dj / (dj - di);
					result.y[m] = y[j] + (y[i]-y[j])*s;
					result.z[m] = z[j] + (z[i]-z[j])*s;
					m++;
				}

				if (curr) {
					result.y[m] = y[i];
					result.z[m] = z[i];
					m++;
				}

				dj = di;
			}

			result.n = m;
		}

		/// <summary>
		/// Clips a polygon against an axis aligned half plane.
		/// The polygons stored in this object are clipped against the half plane at z = -offset.
		/// </summary>
		/// <param name="result">Ouput vertices. Only the Y coordinates are calculated. The X and Z coordinates are undefined.</param>
		/// <param name="multi">Scale factor for the input vertices. Should be +1 or -1. If -1 the negative half plane is kept.</param>
		/// <param name="offset">Offset to move the input vertices with before cutting</param>
		public void ClipPolygonAlongZWithY (ref VoxelPolygonClipper result, float multi, float offset) {
			// Number of resulting vertices
			int m = 0;
			bool prev, curr;

			float dj = multi*z[(n-1)]+offset;

			for (int i = 0, j = n-1; i < n; j = i, i++) {
				float di = multi*z[i]+offset;
				prev = dj >= 0;
				curr = di >= 0;

				if (prev != curr) {
					float s = dj / (dj - di);
					result.y[m] = y[j] + (y[i]-y[j])*s;
					m++;
				}

				if (curr) {
					result.y[m] = y[i];
					m++;
				}

				dj = di;
			}

			result.n = m;
		}
	}

	/// <summary>Utility for clipping polygons</summary>
	internal struct Int3PolygonClipper {
		/// <summary>Cache this buffer to avoid unnecessary allocations</summary>
		float[] clipPolygonCache;

		/// <summary>Cache this buffer to avoid unnecessary allocations</summary>
		int[] clipPolygonIntCache;

		/// <summary>Initialize buffers if they are null</summary>
		public void Init () {
			if (clipPolygonCache == null) {
				clipPolygonCache = new float[7*3];
				clipPolygonIntCache = new int[7*3];
			}
		}

		/// <summary>
		/// Clips a polygon against an axis aligned half plane.
		///
		/// Returns: Number of output vertices
		///
		/// The vertices will be scaled and then offset, after that they will be cut using either the
		/// x axis, y axis or the z axis as the cutting line. The resulting vertices will be added to the
		/// vOut array in their original space (i.e before scaling and offsetting).
		/// </summary>
		/// <param name="vIn">Input vertices</param>
		/// <param name="n">Number of input vertices (may be less than the length of the vIn array)</param>
		/// <param name="vOut">Output vertices, needs to be large enough</param>
		/// <param name="multi">Scale factor for the input vertices</param>
		/// <param name="offset">Offset to move the input vertices with before cutting</param>
		/// <param name="axis">Axis to cut along, either x=0, y=1, z=2</param>
		public int ClipPolygon (Int3[] vIn, int n, Int3[] vOut, int multi, int offset, int axis) {
			Init();
			int[] d = clipPolygonIntCache;

			for (int i = 0; i < n; i++) {
				d[i] = multi*vIn[i][axis]+offset;
			}

			// Number of resulting vertices
			int m = 0;

			for (int i = 0, j = n-1; i < n; j = i, i++) {
				bool prev = d[j] >= 0;
				bool curr = d[i] >= 0;

				if (prev != curr) {
					double s = (double)d[j] / (d[j] - d[i]);

					vOut[m] = vIn[j] + (vIn[i]-vIn[j])*s;
					m++;
				}

				if (curr) {
					vOut[m] = vIn[i];
					m++;
				}
			}

			return m;
		}
	}
}