GdxEarcut.java

package com.badlogic.gdx.tests.lwjgl3;

import com.badlogic.gdx.utils.Array;
import com.badlogic.gdx.utils.IntArray;
import com.badlogic.gdx.utils.Pool;

/**
 * Port of https://github.com/earcut4j/earcut4j for libgdx with 0 allocation
 * Original port of mapbox/earcut
 */
public final class GdxEarcut {

	private GdxEarcut () {
	}

	private static final Pool<Node> nodePool = new Pool<Node>(100, 10000) {
		@Override
		protected Node newObject () {
			return new Node();
		}
	};

	private static final Array<Node> tempQueue = new Array<Node>();
	private static final IntArray triangles = new IntArray();

	public static IntArray earcut (float[] data) {
		return earcut(data, null, 2);
	}

	public static IntArray earcut (float[] data, int[] holeIndices, int dim) {
		boolean hasHoles = holeIndices != null && holeIndices.length > 0;
		int outerLen = hasHoles ? holeIndices[0] * dim : data.length;

		triangles.clear();

		Node outerNode = linkedList(data, 0, outerLen, dim, true);

		if (outerNode == null || outerNode.next == outerNode.prev) {
			if (outerNode != null) {
				freeNode(outerNode);
			}
			return triangles;
		}

		float minX = 0;
		float minY = 0;
		float maxX = 0;
		float maxY = 0;
		float invSize = Float.MIN_VALUE;

		if (hasHoles) {
			outerNode = eliminateHoles(data, holeIndices, outerNode, dim);
		}

		if (data.length > 80 * dim) {
			minX = maxX = data[0];
			minY = maxY = data[1];

			for (int i = dim; i < outerLen; i += dim) {
				float x = data[i];
				float y = data[i + 1];
				if (x < minX) {
					minX = x;
				}
				if (y < minY) {
					minY = y;
				}
				if (x > maxX) {
					maxX = x;
				}
				if (y > maxY) {
					maxY = y;
				}
			}

			invSize = Math.max(maxX - minX, maxY - minY);
			invSize = invSize != 0.0f ? 1.0f / invSize : 0.0f;
		}

		earcutLinked(outerNode, triangles, dim, minX, minY, invSize, Integer.MIN_VALUE);
		return triangles;
	}

	private static void earcutLinked (Node ear, IntArray triangles, int dim, float minX, float minY, float invSize, int pass) {
		if (ear == null) {
			return;
		}

		if (pass == Integer.MIN_VALUE && invSize != Float.MIN_VALUE) {
			indexCurve(ear, minX, minY, invSize);
		}

		Node stop = ear;

		while (ear.prev != ear.next) {
			Node prev = ear.prev;
			Node next = ear.next;

			if (invSize != Float.MIN_VALUE ? isEarHashed(ear, minX, minY, invSize) : isEar(ear)) {
				triangles.add(prev.i / dim);
				triangles.add(ear.i / dim);
				triangles.add(next.i / dim);

				removeNode(ear);

				ear = next.next;
				stop = next.next;

				continue;
			}

			ear = next;

			if (ear == stop) {
				if (pass == Integer.MIN_VALUE) {
					earcutLinked(filterPoints(ear, null), triangles, dim, minX, minY, invSize, 1);

				} else if (pass == 1) {
					ear = cureLocalIntersections(filterPoints(ear, null), triangles, dim);
					earcutLinked(ear, triangles, dim, minX, minY, invSize, 2);

				} else if (pass == 2) {
					splitEarcut(ear, triangles, dim, minX, minY, invSize);
				}

				break;
			}
		}
	}

	private static void splitEarcut (Node start, IntArray triangles, int dim, float minX, float minY, float size) {
		Node a = start;
		do {
			Node b = a.next.next;
			while (b != a.prev) {
				if (a.i != b.i && isValidDiagonal(a, b)) {
					Node c = splitPolygon(a, b);

					a = filterPoints(a, a.next);
					c = filterPoints(c, c.next);

					earcutLinked(a, triangles, dim, minX, minY, size, Integer.MIN_VALUE);
					earcutLinked(c, triangles, dim, minX, minY, size, Integer.MIN_VALUE);
					return;
				}
				b = b.next;
			}
			a = a.next;
		} while (a != start);
	}

	private static boolean isValidDiagonal (Node a, Node b) {
		return a.next.i != b.i && a.prev.i != b.i && !intersectsPolygon(a, b) && (locallyInside(a, b) && locallyInside(b, a) && middleInside(a, b) && (area(a.prev, a, b.prev) != 0 || area(a, b.prev, b) != 0) || equals(a, b) && area(a.prev, a, a.next) > 0 && area(b.prev, b, b.next) > 0);
	}

	private static boolean middleInside (Node a, Node b) {
		Node p = a;
		boolean inside = false;
		float px = (a.x + b.x) * 0.5f;
		float py = (a.y + b.y) * 0.5f;
		do {
			if (((p.y > py) != (p.next.y > py)) && (px < (p.next.x - p.x) * (py - p.y) / (p.next.y - p.y) + p.x)) {
				inside = !inside;
			}
			p = p.next;
		} while (p != a);

		return inside;
	}

	private static boolean intersectsPolygon (Node a, Node b) {
		Node p = a;
		do {
			if (p.i != a.i && p.next.i != a.i && p.i != b.i && p.next.i != b.i && intersects(p, p.next, a, b)) {
				return true;
			}
			p = p.next;
		} while (p != a);

		return false;
	}

	private static boolean intersects (Node p1, Node q1, Node p2, Node q2) {
		if ((equals(p1, p2) && equals(q1, q2)) || (equals(p1, q2) && equals(p2, q1))) {
			return true;
		}

		float o1 = sign(area(p1, q1, p2));
		float o2 = sign(area(p1, q1, q2));
		float o3 = sign(area(p2, q2, p1));
		float o4 = sign(area(p2, q2, q1));

		if (o1 != o2 && o3 != o4) {
			return true;
		}

		if (o1 == 0 && onSegment(p1, p2, q1)) {
			return true;
		}
		if (o2 == 0 && onSegment(p1, q2, q1)) {
			return true;
		}
		if (o3 == 0 && onSegment(p2, p1, q2)) {
			return true;
		}
		if (o4 == 0 && onSegment(p2, q1, q2)) {
			return true;
		}

		return false;
	}

	private static boolean onSegment (Node p, Node q, Node r) {
		return q.x <= Math.max(p.x, r.x) && q.x >= Math.min(p.x, r.x) && q.y <= Math.max(p.y, r.y) && q.y >= Math.min(p.y, r.y);
	}

	private static float sign (float num) {
		return num > 0 ? 1 : num < 0 ? -1 : 0;
	}

	private static Node cureLocalIntersections (Node start, IntArray triangles, int dim) {
		Node p = start;
		do {
			Node a = p.prev, b = p.next.next;

			if (!equals(a, b) && intersects(a, p, p.next, b) && locallyInside(a, b) && locallyInside(b, a)) {

				triangles.add(a.i / dim);
				triangles.add(p.i / dim);
				triangles.add(b.i / dim);

				removeNode(p);
				removeNode(p.next);

				p = start = b;
			}
			p = p.next;
		} while (p != start);

		return filterPoints(p, null);
	}

	private static boolean isEar (Node ear) {
		Node a = ear.prev, b = ear, c = ear.next;

		if (area(a, b, c) >= 0) {
			return false;
		}

		Node p = ear.next.next;

		while (p != ear.prev) {
			if (pointInTriangle(a.x, a.y, b.x, b.y, c.x, c.y, p.x, p.y) && area(p.prev, p, p.next) >= 0) {
				return false;
			}
			p = p.next;
		}

		return true;
	}

	private static boolean isEarHashed (Node ear, float minX, float minY, float invSize) {
		Node a = ear.prev;
		Node b = ear;
		Node c = ear.next;

		if (area(a, b, c) >= 0) {
			return false;
		}

		float minTX, minTY, maxTX, maxTY;
		if (a.x < b.x) {
			if (a.x < c.x) {
				minTX = a.x;
				maxTX = b.x > c.x ? b.x : c.x;
			} else {
				minTX = c.x;
				maxTX = b.x > a.x ? b.x : a.x;
			}
		} else {
			if (b.x < c.x) {
				minTX = b.x;
				maxTX = a.x > c.x ? a.x : c.x;
			} else {
				minTX = c.x;
				maxTX = a.x > b.x ? a.x : b.x;
			}
		}

		if (a.y < b.y) {
			if (a.y < c.y) {
				minTY = a.y;
				maxTY = b.y > c.y ? b.y : c.y;
			} else {
				minTY = c.y;
				maxTY = b.y > a.y ? b.y : a.y;
			}
		} else {
			if (b.y < c.y) {
				minTY = b.y;
				maxTY = a.y > c.y ? a.y : c.y;
			} else {
				minTY = c.y;
				maxTY = a.y > b.y ? a.y : b.y;
			}
		}

		float minZ = zOrder(minTX, minTY, minX, minY, invSize);
		float maxZ = zOrder(maxTX, maxTY, minX, minY, invSize);

		Node p = ear.prevZ;
		Node n = ear.nextZ;

		while (p != null && p.z >= minZ && n != null && n.z <= maxZ) {
			if (p != ear.prev && p != ear.next && pointInTriangle(a.x, a.y, b.x, b.y, c.x, c.y, p.x, p.y) && area(p.prev, p, p.next) >= 0) {
				return false;
			}
			p = p.prevZ;

			if (n != ear.prev && n != ear.next && pointInTriangle(a.x, a.y, b.x, b.y, c.x, c.y, n.x, n.y) && area(n.prev, n, n.next) >= 0) {
				return false;
		}
			n = n.nextZ;
		}

		while (p != null && p.z >= minZ) {
			if (p != ear.prev && p != ear.next && pointInTriangle(a.x, a.y, b.x, b.y, c.x, c.y, p.x, p.y) && area(p.prev, p, p.next) >= 0) {
				return false;
			}
			p = p.prevZ;
		}

		while (n != null && n.z <= maxZ) {
			if (n != ear.prev && n != ear.next && pointInTriangle(a.x, a.y, b.x, b.y, c.x, c.y, n.x, n.y) && area(n.prev, n, n.next) >= 0) {
				return false;
			}
			n = n.nextZ;
		}

		return true;
	}

	private static float zOrder (float x, float y, float minX, float minY, float invSize) {
		int lx = (int)(32767 * (x - minX) * invSize);
		int ly = (int)(32767 * (y - minY) * invSize);

		lx = (lx | (lx << 8)) & 0x00FF00FF;
		lx = (lx | (lx << 4)) & 0x0F0F0F0F;
		lx = (lx | (lx << 2)) & 0x33333333;
		lx = (lx | (lx << 1)) & 0x55555555;

		ly = (ly | (ly << 8)) & 0x00FF00FF;
		ly = (ly | (ly << 4)) & 0x0F0F0F0F;
		ly = (ly | (ly << 2)) & 0x33333333;
		ly = (ly | (ly << 1)) & 0x55555555;

		return lx | (ly << 1);
	}

	private static void indexCurve (Node start, float minX, float minY, float invSize) {
		Node p = start;
		do {
			if (p.z == Float.MIN_VALUE) {
				p.z = zOrder(p.x, p.y, minX, minY, invSize);
			}
			p.prevZ = p.prev;
			p.nextZ = p.next;
			p = p.next;
		} while (p != start);

		p.prevZ.nextZ = null;
		p.prevZ = null;

		sortLinked(p);
	}

	private static Node sortLinked (Node list) {
		int inSize = 1;

		int numMerges;
		do {
			Node p = list;
			list = null;
			Node tail = null;
			numMerges = 0;

			while (p != null) {
				numMerges++;
				Node q = p;
				int pSize = 0;
				for (int i = 0; i < inSize; i++) {
					pSize++;
					q = q.nextZ;
					if (q == null) {
						break;
					}
				}

				int qSize = inSize;

				while (pSize > 0 || (qSize > 0 && q != null)) {
					Node e;
					if (pSize == 0) {
						e = q;
						q = q.nextZ;
						qSize--;
					} else if (qSize == 0 || q == null) {
						e = p;
						p = p.nextZ;
						pSize--;
					} else if (p.z <= q.z) {
						e = p;
						p = p.nextZ;
						pSize--;
					} else {
						e = q;
						q = q.nextZ;
						qSize--;
					}

					if (tail != null) {
						tail.nextZ = e;
					} else {
						list = e;
					}

					e.prevZ = tail;
					tail = e;
				}

				p = q;
			}

			tail.nextZ = null;
			inSize *= 2;

		} while (numMerges > 1);

		return list;
	}

	private static Node eliminateHoles (float[] data, int[] holeIndices, Node outerNode, int dim) {
		tempQueue.clear();

		int len = holeIndices.length;
		for (int i = 0; i < len; i++) {
			int start = holeIndices[i] * dim;
			int end = i < len - 1 ? holeIndices[i + 1] * dim : data.length;
			Node list = linkedList(data, start, end, dim, false);
			if (list == list.next) {
				list.steiner = true;
			}
			tempQueue.add(getLeftmost(list));
		}

		tempQueue.sort((o1, o2) -> Float.compare(o1.x, o2.x));

		for (int i = 0; i < tempQueue.size; i++) {
			eliminateHole(tempQueue.get(i), outerNode);
			outerNode = filterPoints(outerNode, outerNode.next);
		}

		return outerNode;
	}

	private static Node filterPoints (Node start, Node end) {
		if (start == null) {
			return start;
		}
		if (end == null) {
			end = start;
		}

		Node p = start;
		boolean again;

		do {
			again = false;

			if (!p.steiner && (equals(p, p.next) || area(p.prev, p, p.next) == 0)) {
				removeNode(p);
				p = end = p.prev;
				if (p == p.next) {
					break;
				}
				again = true;
			} else {
				p = p.next;
			}
		} while (again || p != end);

		return end;
	}

	private static boolean equals (Node p1, Node p2) {
		return p1.x == p2.x && p1.y == p2.y;
	}

	private static float area (Node p, Node q, Node r) {
		return (q.y - p.y) * (r.x - q.x) - (q.x - p.x) * (r.y - q.y);
	}

	private static void eliminateHole (Node hole, Node outerNode) {
		outerNode = findHoleBridge(hole, outerNode);
		if (outerNode != null) {
			Node b = splitPolygon(outerNode, hole);

			filterPoints(outerNode, outerNode.next);
			filterPoints(b, b.next);
		}
	}

	private static Node splitPolygon (Node a, Node b) {
		Node a2 = obtainNode(a.i, a.x, a.y);
		Node b2 = obtainNode(b.i, b.x, b.y);
		Node an = a.next;
		Node bp = b.prev;

		a.next = b;
		b.prev = a;

		a2.next = an;
		an.prev = a2;

		b2.next = a2;
		a2.prev = b2;

		bp.next = b2;
		b2.prev = bp;

		return b2;
	}

	private static Node findHoleBridge (Node hole, Node outerNode) {
		Node p = outerNode;
		float hx = hole.x;
		float hy = hole.y;
		float qx = -Float.MAX_VALUE;
		Node m = null;

		do {
			if (hy <= p.y && hy >= p.next.y && p.next.y != p.y) {
				float x = p.x + (hy - p.y) * (p.next.x - p.x) / (p.next.y - p.y);
				if (x <= hx && x > qx) {
					qx = x;
					if (x == hx) {
						if (hy == p.y) {
							return p;
						}
						if (hy == p.next.y) {
							return p.next;
						}
					}
					m = p.x < p.next.x ? p : p.next;
				}
			}
			p = p.next;
		} while (p != outerNode);

		if (m == null) {
			return null;
		}

		if (hx == qx) {
			return m;
		}

		Node stop = m;
		float mx = m.x;
		float my = m.y;
		float tanMin = Float.MAX_VALUE;
		float tan;

		p = m;

		do {
			if (hx >= p.x && p.x >= mx && hx != p.x && pointInTriangle(hy < my ? hx : qx, hy, mx, my, hy < my ? qx : hx, hy, p.x, p.y)) {

				tan = Math.abs(hy - p.y) / (hx - p.x);

				if (locallyInside(p, hole) && (tan < tanMin || (tan == tanMin && (p.x > m.x || (p.x == m.x && sectorContainsSector(m, p)))))) {
					m = p;
					tanMin = tan;
				}
			}

			p = p.next;
		} while (p != stop);

		return m;
	}

	private static boolean locallyInside (Node a, Node b) {
		if (area(a.prev, a, a.next) < 0) {
			return area(a, b, a.next) >= 0 && area(a, a.prev, b) >= 0;
		} else {
			return area(a, b, a.prev) < 0 || area(a, a.next, b) < 0;
		}
	}

	private static boolean sectorContainsSector (Node m, Node p) {
		return area(m.prev, m, p.prev) < 0 && area(p.next, m, m.next) < 0;
	}

	private static boolean pointInTriangle (float ax, float ay, float bx, float by, float cx, float cy, float px, float py) {
		return (cx - px) * (ay - py) - (ax - px) * (cy - py) >= 0 && (ax - px) * (by - py) - (bx - px) * (ay - py) >= 0 && (bx - px) * (cy - py) - (cx - px) * (by - py) >= 0;
	}

	private static Node getLeftmost (Node start) {
		Node p = start;
		Node leftmost = start;
		do {
			if (p.x < leftmost.x || (p.x == leftmost.x && p.y < leftmost.y)) {
				leftmost = p;
			}
			p = p.next;
		} while (p != start);
		return leftmost;
	}

	private static Node linkedList (float[] data, int start, int end, int dim, boolean clockwise) {
		Node last = null;
		if (clockwise == (signedArea(data, start, end, dim) > 0)) {
			for (int i = start; i < end; i += dim) {
				last = insertNode(i, data[i], data[i + 1], last);
			}
		} else {
			for (int i = (end - dim); i >= start; i -= dim) {
				last = insertNode(i, data[i], data[i + 1], last);
			}
		}

		if (last != null && equals(last, last.next)) {
			removeNode(last);
			last = last.next;
		}
		return last;
	}

	private static void removeNode (Node p) {
		p.next.prev = p.prev;
		p.prev.next = p.next;

		if (p.prevZ != null) {
			p.prevZ.nextZ = p.nextZ;
		}
		if (p.nextZ != null) {
			p.nextZ.prevZ = p.prevZ;
		}

		freeNode(p);
	}

	private static Node insertNode (int i, float x, float y, Node last) {
		Node p = obtainNode(i, x, y);

		if (last == null) {
			p.prev = p;
			p.next = p;
		} else {
			p.next = last.next;
			p.prev = last;
			last.next.prev = p;
			last.next = p;
		}
		return p;
	}

	private static float signedArea (float[] data, int start, int end, int dim) {
		float sum = 0;
		int j = end - dim;
		for (int i = start; i < end; i += dim) {
			sum += (data[j] - data[i]) * (data[i + 1] + data[j + 1]);
			j = i;
		}
		return sum;
	}

	private static Node obtainNode (int i, float x, float y) {
		Node node = nodePool.obtain();
		node.reset(i, x, y);
		return node;
	}

	private static void freeNode (Node node) {

		if (node != null) {
			nodePool.free(node);
		}
	}

	private static void freeLinkedList (Node start) {
		if (start == null) {
			return;
		}

		Node current = start;
		boolean first = true;
		while (current != null && (first || current != start)) {
			first = false;
			Node next = current.next;
			freeNode(current);
			current = next;
		}
	}

	private static class Node implements Pool.Poolable {
		int i;
		float x;
		float y;
		float z;
		boolean steiner;

		Node prev;
		Node next;
		Node prevZ;
		Node nextZ;

		Node () {
		}

		void reset (int i, float x, float y) {
			this.i = i;
			this.x = x;
			this.y = y;
			this.prev = null;
			this.next = null;
			this.z = Float.MIN_VALUE;
			this.prevZ = null;
			this.nextZ = null;
			this.steiner = false;
		}

		@Override
		public void reset () {
			this.i = 0;
			this.x = 0;
			this.y = 0;
			this.z = Float.MIN_VALUE;
			this.steiner = false;
			this.prev = null;
			this.next = null;
			this.prevZ = null;
			this.nextZ = null;
		}
	}
}