implement edge collapse to further improve eikmesh.

VadereMeshing/src/org/vadere/meshing/examples/EikMeshPoly.java

@@ -61,14 +61,14 @@ public class EikMeshPoly {
 				pslg.getAllPolygons()
 		);
 
-		var meshPanel = new PMeshPanel(meshImprover.getMesh()/*, f -> distanceFunction.apply(meshImprover.getMesh().toTriangle(f).midPoint()) > 0*/, 1000, 800);
+		var meshPanel = new PMeshPanel(meshImprover.getMesh(), f -> meshImprover.getMesh().getBooleanData(f, "frozen"), 1000, 800);
 		meshPanel.display("Combined distance functions " + h0);
 		meshImprover.improve();
 		while (!meshImprover.isFinished()) {
 			synchronized (meshImprover.getMesh()) {
 				meshImprover.improve();
 			}
-			//Thread.sleep(200);
+			//Thread.sleep(2000);
 			meshPanel.repaint();
 		}
 		//meshImprover.generate();

VadereMeshing/src/org/vadere/meshing/mesh/inter/ITriConnectivity.java

@@ -15,7 +15,6 @@ import org.vadere.util.geometry.shapes.VTriangle;
 import org.vadere.util.logging.Logger;
 import org.vadere.util.math.IDistanceFunction;
 
-import java.lang.reflect.Array;
 import java.util.ArrayList;
 import java.util.LinkedList;
 import java.util.List;
@@ -29,7 +28,7 @@ import java.util.stream.Collectors;
 /**
  * <p>A tri-connectivity {@link ITriConnectivity} is the connectivity of a mesh of non-intersecting connected triangles including holes.
  * A hole can be an arbitrary simple polygon. So it is more concrete than a poly-connectivity {@link IPolyConnectivity}.
- * The mesh {@link IMesh} stores all the date of the base elements (points {@link P}, vertices {@link V}, half-edges {@link E}
+ * The mesh {@link IMesh} stores all the date of the base elements (vertices {@link V}, half-edges {@link E}
  * and faces {@link F}) and offers factory method to create new base elements.
  * The connectivities, i.e. {@link IPolyConnectivity} and {@link ITriConnectivity} offers all the operations manipulating
  * the connectivity of the mesh. The connectivity is the relation between vertices and edges which define faces which therefore define the mesh structure.</p>
@@ -205,6 +204,20 @@ public interface ITriConnectivity<V extends IVertex, E extends IHalfEdge, F exte
 		return getMesh().toLine(next).lengthSq() <= lenSq && getMesh().toLine(prev).lengthSq() <= lenSq;
 	}
 
+	default boolean isShortestHalfEdge(@NotNull final E edge) {
+		E e = edge;
+		if(getMesh().isBoundary(e)) {
+			e = getMesh().getTwin(e);
+		}
+
+		E next = getMesh().getNext(e);
+		E prev = getMesh().getPrev(e);
+		VLine line = getMesh().toLine(e);
+		double lenSq = line.lengthSq();
+
+		return getMesh().toLine(next).lengthSq() >= lenSq && getMesh().toLine(prev).lengthSq() >= lenSq;
+	}
+
 	/**
 	 * <p>Inserts a point into the mesh which is contained in a boundary by connecting the boundaryEdge
 	 * to the point in O(1) time. This will create 4 new half-edges, one new vertex and one face.</p>
@@ -1223,6 +1236,104 @@ public interface ITriConnectivity<V extends IVertex, E extends IHalfEdge, F exte
 		return splitTriangle(face, p, true);
 	}
 
+	default V collapseEdge(@NotNull final E edge, final boolean deleteIsolatededVertex) {
+		IMesh<V, E, F> mesh = getMesh();
+		E twin = mesh.getTwin(edge);
+
+		// before changing connectivity change vertices.
+		V replacedVertex = getMesh().getVertex(twin);
+		V survivedVertex = getMesh().getVertex(edge);
+
+		for(E e : getMesh().getEdgeIt(replacedVertex)) {
+			getMesh().setVertex(e, survivedVertex);
+		}
+
+		if(getMesh().getEdge(survivedVertex).equals(edge)) {
+			getMesh().setEdge(survivedVertex, getMesh().getTwin(getMesh().getNext(edge)));
+		}
+
+		F fa = mesh.getFace(edge);
+		F fb = mesh.getFace(twin);
+
+		F f4 = getMesh().getTwinFace(getMesh().getPrev(edge));
+		F f5 = getMesh().getTwinFace(getMesh().getNext(twin));
+
+		boolean isF4Boundary = getMesh().isBoundary(f4);
+		boolean isF5Boundary = getMesh().isBoundary(f5);
+
+		// survives
+		E aNext = mesh.getNext(edge);
+		E bNext = mesh.getNext(twin);
+		E aPrev = mesh.getPrev(edge);
+		// survives
+		E bPrev = mesh.getPrev(twin);
+
+		if(!getMesh().isBoundary(edge)) {
+			E aPrevTwin = mesh.getTwin(aPrev);
+			E aPrevTwinPrev = mesh.getPrev(aPrevTwin);
+			E aPrevTwinNext = mesh.getNext(aPrevTwin);
+			E next = getMesh().getNext(edge);
+			V nextVertex = getMesh().getVertex(next);
+
+			if(getMesh().getEdge(nextVertex).equals(aPrevTwin)) {
+				getMesh().setEdge(nextVertex, next);
+			}
+
+			// adjust pointers
+			getMesh().setNext(aNext, aPrevTwinNext);
+			getMesh().setPrev(aNext, aPrevTwinPrev);
+			getMesh().setFace(aNext, f4);
+			getMesh().setEdge(f4, aNext);
+
+			// destroy the rest
+			getMesh().destroyFace(fa);
+			getMesh().destroyEdge(aPrev);
+			getMesh().destroyEdge(aPrevTwin);
+		} else {
+			getMesh().setNext(getMesh().getPrev(edge), getMesh().getNext(edge));
+		}
+
+		if(!getMesh().isBoundary(twin)) {
+			E bNextTwin = mesh.getTwin(bNext);
+			E bNextTwinNext = mesh.getNext(bNextTwin);
+			E bNextTwinPrev = mesh.getPrev(bNextTwin);
+			E prevTwin = getMesh().getTwin(mesh.getPrev(twin));
+			V nextVertex = getMesh().getVertex(prevTwin);
+
+			if(getMesh().getEdge(nextVertex).equals(bNext)) {
+				getMesh().setEdge(nextVertex, prevTwin);
+			}
+
+			// adjust pointers
+			getMesh().setNext(bPrev, bNextTwinNext);
+			getMesh().setPrev(bPrev, bNextTwinPrev);
+			getMesh().setFace(bPrev, f5);
+			getMesh().setEdge(f5, bPrev);
+
+			// destroy the rest
+			getMesh().destroyFace(fb);
+			getMesh().destroyEdge(bNext);
+			getMesh().destroyEdge(bNextTwin);
+		} else {
+			getMesh().setNext(getMesh().getPrev(twin), getMesh().getNext(twin));
+		}
+
+		// destroy the rest
+		getMesh().destroyEdge(edge);
+		getMesh().destroyEdge(twin);
+
+		if(deleteIsolatededVertex) {
+			getMesh().destroyVertex(replacedVertex);
+		} else {
+			getMesh().setEdge(replacedVertex, null);
+		}
+
+		adjustVertex(survivedVertex);
+		assert getMesh().isValid();
+
+		return survivedVertex;
+	}
+
 	/**
 	 * <p>This method collapses a three degree vertex which is at the boundary by removing the
 	 * one edge (a simple link) which is not a boundary edge and by merging the two other boundary edges,

VadereMeshing/src/org/vadere/meshing/mesh/triangulation/improver/distmesh/Parameters.java

@@ -14,7 +14,7 @@ public class Parameters {
 	public final static double h0 = 0.15;
 	public final static boolean uniform = false;
 	public final static String method = "Distmesh"; // "Distmesh" or "Density"
-    public final static double qualityMeasurement = 0.90;
+    public final static double qualityMeasurement = 0.85;
     public final static double MINIMUM = 0.25;
     public final static double DENSITYWEIGHT = 2;
     public final static int NPOINTS = 100000;

VadereMeshing/src/org/vadere/meshing/mesh/triangulation/improver/eikmesh/gen/GenEikMesh.java

 package org.vadere.meshing.mesh.triangulation.improver.eikmesh.gen;
 
 import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
 import org.vadere.meshing.mesh.IllegalMeshException;
 import org.vadere.meshing.mesh.inter.IFace;
 import org.vadere.meshing.mesh.inter.IHalfEdge;
@@ -90,15 +89,21 @@ public class GenEikMesh<V extends IVertex, E extends IHalfEdge, F extends IFace>
 	// different options
 	private boolean allowEdgeSplits = true;
 	private boolean allowVertexCollapse = true;
+	private boolean allowEdgeCollapse = true;
 	private boolean removeLowBoundaryTriangles = false;
 	private boolean useVirtualEdges = true;
 	private boolean smoothBorder = false;
+	private boolean freezeVertices = true;
 	//private boolean splitFaces = true;
 	//private boolean useFixPoints = false;
 
 	// only for logging
     private static final Logger log = Logger.getLogger(GenEikMesh.class);
 
+    static {
+    	log.setDebug();
+    }
+
 
     // properties saved for different mesh elements i.e. vertices, edges and faces
 	private static final String propFixPoint = "fixPoint";
@@ -348,6 +353,13 @@ public class GenEikMesh<V extends IVertex, E extends IHalfEdge, F extends IFace>
 		return getTriangulation().getMesh();
 	}
 
+	private void freezeVertices() {
+		if(freezeVertices) {
+			getMesh().streamVertices().filter(v -> getMesh().streamFaces(v).filter(f -> !getMesh().isBoundary(f)).allMatch(f -> faceToQuality(f) > Parameters.qualityMeasurement)).forEach(v -> setFixPoint(v, true));
+			getMesh().streamFaces().filter(f -> getMesh().streamVertices(f).allMatch(v -> isFixPoint(v))).forEach(f -> getMesh().setBooleanData(f, "frozen", true));
+		}
+	}
+
 	@Override
     public void improve() {
 		synchronized (getMesh()) {
@@ -390,6 +402,7 @@ public class GenEikMesh<V extends IVertex, E extends IHalfEdge, F extends IFace>
 				//computeBoundaryForces();
 				updateEdges();
 				updateVertices();
+				freezeVertices();
 				nSteps++;
 
 
@@ -752,7 +765,45 @@ public class GenEikMesh<V extends IVertex, E extends IHalfEdge, F extends IFace>
 	 * Updates all boundary edges. Some of those edges might get split.
 	 */
 	private void updateEdges() {
-		getMesh().getBoundaryEdges().forEach(e -> updateEdge(e));
+		getMesh().getBoundaryEdges().forEach(e -> updateBoundaryEdges(e));
+		if(allowEdgeCollapse) {
+			for(E e : getMesh().getEdges()) {
+				if(!getMesh().isDestroyed(e) && !getMesh().isAtBoundary(e)) {
+					if(updateEdge(e)) {
+					}
+				}
+			}
+		}
+	}
+
+	private boolean updateEdge(@NotNull final E edge) {
+		if(getTriangulation().isShortestHalfEdge(edge) &&
+				(faceToQuality(getMesh().getFace(edge)) < Parameters.MIN_SPLIT_TRIANGLE_QUALITY
+						|| faceToQuality(getMesh().getTwinFace(edge)) < Parameters.MIN_SPLIT_TRIANGLE_QUALITY)) {
+			V v1 = getMesh().getVertex(edge);
+			V v2 = getMesh().getTwinVertex(edge);
+
+			if(!getMesh().isAtBoundary(v1) || !getMesh().isAtBoundary(v2)) {
+				VPoint newPosition;
+				if(getMesh().isAtBoundary(v1)) {
+					newPosition = new VPoint(v1.getX(), v1.getY());
+				} else if(getMesh().isAtBoundary(v2)) {
+					newPosition = new VPoint(v2.getX(), v2.getY());
+				} else {
+					newPosition = new VPoint((v1.getX() + v2.getX()) * 0.5, (v1.getY() + v2.getY()) * 0.5);
+				}
+
+				if(isLegalMove(getMesh().getVertex(edge), newPosition.getX(), newPosition.getY()) &&
+						isLegalMove(getMesh().getTwinVertex(edge), newPosition.getX(), newPosition.getY())) {
+					V v = getTriangulation().collapseEdge(edge, true);
+					getMesh().setPoint(v, newPosition);
+					log.debug("edge collapse");
+				}
+
+				return true;
+			}
+		}
+		return false;
 	}
 
 	/**
@@ -760,7 +811,7 @@ public class GenEikMesh<V extends IVertex, E extends IHalfEdge, F extends IFace>
 	 *
 	 * @param edge the edge
 	 */
-	private void updateEdge(@NotNull final E edge) {
+	private void updateBoundaryEdges(@NotNull final E edge) {
 		if(canBreak(edge) && isBreaking(edge)) {
 			//if(distanceFunc == null) {
 				V v1 = getMesh().getVertex(edge);