Allow applying repulsion force between springs (#93)

* allow applying repulsion force between springs
* spring repulsion as a factor of repulsion between points
* unit test
* Apply repulsion between node and spring also to end nodes of spring

Signed-off-by: Luma <zamarrenolm@aia.es>

src/main/java/com/powsybl/forcelayout/ForceLayout.java

@@ -61,13 +61,15 @@ public class ForceLayout<V, E> {
     private static final double DEFAULT_REPULSION = 800.0;
     private static final double DEFAULT_FRICTION = 500;
     private static final double DEFAULT_MAX_SPEED = 100;
+    private static final double DEFAULT_SPRING_REPULSION_FACTOR = 0.0; // Disabled by default
 
     private int maxSteps;
     private double minEnergyThreshold;
     private double deltaTime;
     private double repulsion;
     private double friction;
     private double maxSpeed;
+    private double springRepulsionFactor;
 
     private final Graph<V, E> graph;
     private final Map<V, Point> points = new LinkedHashMap<>();
@@ -82,6 +84,7 @@ public ForceLayout(Graph<V, E> graph) {
         this.repulsion = DEFAULT_REPULSION;
         this.friction = DEFAULT_FRICTION;
         this.maxSpeed = DEFAULT_MAX_SPEED;
+        this.springRepulsionFactor = DEFAULT_SPRING_REPULSION_FACTOR;
 
         this.graph = Objects.requireNonNull(graph);
     }
@@ -116,6 +119,11 @@ public ForceLayout<V, E> setMaxSpeed(double maxSpeed) {
         return this;
     }
 
+    public ForceLayout<V, E> setSpringRepulsionFactor(double springRepulsionFactor) {
+        this.springRepulsionFactor = springRepulsionFactor;
+        return this;
+    }
+
     private void initializePoints() {
         for (V vertex : graph.vertexSet()) {
             points.put(vertex, new Point(random.nextDouble(), random.nextDouble()));
@@ -140,7 +148,10 @@ public void execute() {
 
         int i;
         for (i = 0; i < maxSteps; i++) {
-            applyCoulombsLaw();
+            applyCoulombsLawToPoints();
+            if (springRepulsionFactor != 0.0) {
+                applyCoulombsLawToSprings();
+            }
             applyHookesLaw();
             attractToCenter();
             updateVelocity();
@@ -159,15 +170,57 @@ public void execute() {
         LOGGER.info("Elapsed time: {}", elapsedTime / 1e9);
     }
 
-    private void applyCoulombsLaw() {
+    private Vector coulombsForce(Vector p1, Vector p2, double repulsion) {
+        Vector distance = p1.subtract(p2);
+        Vector direction = distance.normalize();
+        return direction.multiply(repulsion).divide(distance.magnitudeSquare() * 0.5 + 0.1);
+    }
+
+    private void applyCoulombsLawToPoints() {
         for (Point point : points.values()) {
+            Vector p = point.getPosition();
             for (Point otherPoint : points.values()) {
                 if (!point.equals(otherPoint)) {
-                    Vector distance = point.getPosition().subtract(otherPoint.getPosition());
-                    Vector direction = distance.normalize();
+                    point.applyForce(coulombsForce(p, otherPoint.getPosition(), repulsion));
+                }
+            }
+        }
+    }
 
-                    Vector force = direction.multiply(repulsion).divide(distance.magnitudeSquare() * 0.5 + 0.1);
+    private void applyCoulombsLawToSprings() {
+        for (Point point : points.values()) {
+            Vector p = point.getPosition();
+            for (Spring spring : springs) {
+                Point n1 = spring.getNode1();
+                Point n2 = spring.getNode2();
+                if (!n1.equals(point) && !n2.equals(point)) {
+                    Vector q1 = spring.getNode1().getPosition();
+                    Vector q2 = spring.getNode2().getPosition();
+                    Vector center = q1.add(q2.subtract(q1).multiply(0.5));
+                    Vector force = coulombsForce(p, center, repulsion * springRepulsionFactor);
                     point.applyForce(force);
+                    n1.applyForce(force.multiply(-0.5));
+                    n2.applyForce(force.multiply(-0.5));
+                }
+            }
+        }
+        for (Spring spring : springs) {
+            Point n1 = spring.getNode1();
+            Point n2 = spring.getNode2();
+            Vector p1 = spring.getNode1().getPosition();
+            Vector p2 = spring.getNode2().getPosition();
+            Vector center = p1.add(p2.subtract(p1).multiply(0.5));
+            for (Spring otherSpring : springs) {
+                if (!spring.equals(otherSpring)) {
+                    // Compute the repulsion force between centers of the springs
+                    Vector op1 = otherSpring.getNode1().getPosition();
+                    Vector op2 = otherSpring.getNode2().getPosition();
+                    Vector otherCenter = op1.add(op2.subtract(op1).multiply(0.5));
+                    Vector force = coulombsForce(center, otherCenter, repulsion * springRepulsionFactor);
+
+                    // And apply it to both points of the spring
+                    n1.applyForce(force);
+                    n2.applyForce(force);
                 }
             }
         }

src/main/java/com/powsybl/nad/layout/BasicForceLayout.java

@@ -23,6 +23,7 @@ public class BasicForceLayout extends AbstractLayout {
     protected void nodesLayout(Graph graph, LayoutParameters layoutParameters) {
         org.jgrapht.Graph<Node, Edge> jgraphtGraph = graph.getJgraphtGraph(layoutParameters.isTextNodesForceLayout());
         ForceLayout<Node, Edge> forceLayout = new ForceLayout<>(jgraphtGraph);
+        forceLayout.setSpringRepulsionFactor(layoutParameters.getSpringRepulsionFactorForceLayout());
         forceLayout.execute();
 
         jgraphtGraph.vertexSet().forEach(node -> {

src/main/java/com/powsybl/nad/layout/LayoutParameters.java

@@ -11,12 +11,14 @@
  */
 public class LayoutParameters {
     private boolean textNodesForceLayout = false;
+    private double springRepulsionFactorForceLayout = 0.0;
 
     public LayoutParameters() {
     }
 
     public LayoutParameters(LayoutParameters other) {
         this.textNodesForceLayout = other.textNodesForceLayout;
+        this.springRepulsionFactorForceLayout = other.springRepulsionFactorForceLayout;
     }
 
     public boolean isTextNodesForceLayout() {
@@ -27,4 +29,13 @@ public LayoutParameters setTextNodesForceLayout(boolean textNodesForceLayout) {
         this.textNodesForceLayout = textNodesForceLayout;
         return this;
     }
+
+    public LayoutParameters setSpringRepulsionFactorForceLayout(double springRepulsionFactorForceLayout) {
+        this.springRepulsionFactorForceLayout = springRepulsionFactorForceLayout;
+        return this;
+    }
+
+    public double getSpringRepulsionFactorForceLayout() {
+        return springRepulsionFactorForceLayout;
+    }
 }

src/test/java/com/powsybl/nad/layout/ForceLayoutTest.java

@@ -0,0 +1,170 @@
+/**
+ * Copyright (c) 2022, RTE (http://www.rte-france.com)
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+package com.powsybl.nad.layout;
+
+import com.powsybl.iidm.network.*;
+import com.powsybl.nad.AbstractTest;
+import com.powsybl.nad.svg.LabelProvider;
+import com.powsybl.nad.svg.StyleProvider;
+import com.powsybl.nad.svg.SvgParameters;
+import com.powsybl.nad.svg.iidm.DefaultLabelProvider;
+import com.powsybl.nad.svg.iidm.NominalVoltageStyleProvider;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * @author Luma Zamarreno <zamarrenolm at aia.es>
+ */
+class ForceLayoutTest extends AbstractTest {
+
+    @BeforeEach
+    public void setup() {
+        setLayoutParameters(new LayoutParameters().setTextNodesForceLayout(false));
+        setSvgParameters(new SvgParameters()
+                .setInsertNameDesc(false)
+                .setSvgWidthAndHeightAdded(false));
+    }
+
+    @Override
+    protected StyleProvider getStyleProvider(Network network) {
+        return new NominalVoltageStyleProvider(network);
+    }
+
+    @Override
+    protected LabelProvider getLabelProvider(Network network) {
+        return new DefaultLabelProvider(network, getSvgParameters());
+    }
+
+    @Test
+    void testDiamondNoSpringRepulsionFactor() {
+        assertEquals(
+                toString("/diamond-spring-repulsion-factor-0.0.svg"),
+                generateSvgString(createDiamondNetwork(), "/diamond-spring-repulsion-factor-0.0.svg"));
+    }
+
+    @Test
+    void testDiamondSmallSpringRepulsionFactor() {
+        getLayoutParameters().setSpringRepulsionFactorForceLayout(0.2);
+        assertEquals(
+                toString("/diamond-spring-repulsion-factor-0.2.svg"),
+                generateSvgString(createDiamondNetwork(), "/diamond-spring-repulsion-factor-0.2.svg"));
+    }
+
+    static Network createDiamondNetwork() {
+        Network network = NetworkFactory.findDefault().createNetwork("diamond", "manual");
+        network.setName("diamond");
+
+        Substation subA = network.newSubstation().setId("A").add();
+        Bus subA400 = createBus(subA, 400);
+        Bus subA230 = createBus(subA, 230);
+        createTransformer(subA400, subA230);
+
+        Substation subB = network.newSubstation().setId("B").add();
+        Bus subB230 = createBus(subB, 230);
+        createLine(subA230, subB230);
+
+        Substation subC = network.newSubstation().setId("C").add();
+        Bus subC230 = createBus(subC, 230);
+        Bus subC66 = createBus(subC, 66);
+        Bus subC20 = createBus(subC, 20);
+        createTransformer(subC230, subC66);
+        createTransformer(subC66, subC20);
+        createLine(subB230, subC230);
+
+        Substation subD = network.newSubstation().setId("D").add();
+        Bus subD66 = createBus(subD, 66);
+        Bus subD10 = createBus(subD, 10);
+        createTransformer(subD66, subD10);
+        createLine(subC66, subD66);
+
+        Substation subE = network.newSubstation().setId("E").add();
+        Bus subE10 = createBus(subE, 10);
+        createLine(subD10, subE10);
+
+        Bus subF10 = createBus(network, "F", 10);
+        Bus subG10 = createBus(network, "G", 10);
+        Bus subH10 = createBus(network, "H", 10);
+        Bus subI10 = createBus(network, "I", 10);
+        Bus subJ10 = createBus(network, "J", 10);
+        Bus subK10 = createBus(network, "K", 10);
+
+        createLine(subE10, subF10);
+        createLine(subF10, subG10);
+        createLine(subG10, subH10);
+        createLine(subH10, subD10);
+
+        createLine(subF10, subI10);
+        createLine(subI10, subJ10);
+        createLine(subJ10, subK10);
+        createLine(subK10, subD10);
+
+        return network;
+    }
+
+    private static Bus createBus(Network network, String substationId, double nominalVoltage) {
+        Substation substation = network.newSubstation().setId(substationId).add();
+        return createBus(substation, nominalVoltage);
+    }
+
+    private static Bus createBus(Substation substation, double nominalVoltage) {
+        String vlId = String.format("%s %.0f", substation.getId(), nominalVoltage);
+        String busId = String.format("%s %s", vlId, "Bus");
+        return substation.newVoltageLevel()
+                .setId(vlId)
+                .setNominalV(nominalVoltage)
+                .setTopologyKind(TopologyKind.BUS_BREAKER)
+                .add()
+                .getBusBreakerView()
+                .newBus()
+                .setId(busId)
+                .add();
+    }
+
+    private static void createTransformer(Bus bus1, Bus bus2) {
+        Substation substation = bus1.getVoltageLevel().getSubstation().orElseThrow();
+        String id = String.format("%s %.0f %.0f",
+                substation.getId(),
+                bus1.getVoltageLevel().getNominalV(),
+                bus2.getVoltageLevel().getNominalV());
+        substation.newTwoWindingsTransformer().setId(id)
+                .setR(0.0)
+                .setX(1.0)
+                .setG(0.0)
+                .setB(0.0)
+                .setVoltageLevel1(bus1.getVoltageLevel().getId())
+                .setVoltageLevel2(bus2.getVoltageLevel().getId())
+                .setConnectableBus1(bus1.getId())
+                .setConnectableBus2(bus2.getId())
+                .setRatedU1(bus1.getVoltageLevel().getNominalV())
+                .setRatedU2(bus2.getVoltageLevel().getNominalV())
+                .setBus1(bus1.getId())
+                .setBus2(bus2.getId())
+                .add();
+    }
+
+    private static void createLine(Bus bus1, Bus bus2) {
+        String id = String.format("%s - %s",
+                bus1.getVoltageLevel().getSubstation().orElseThrow().getId(),
+                bus2.getVoltageLevel().getSubstation().orElseThrow().getId());
+        bus1.getNetwork().newLine().setId(id)
+                .setR(0.0)
+                .setX(1.0)
+                .setG1(0.0)
+                .setB1(0.0)
+                .setG2(0.0)
+                .setB2(0.0)
+                .setVoltageLevel1(bus1.getVoltageLevel().getId())
+                .setVoltageLevel2(bus2.getVoltageLevel().getId())
+                .setConnectableBus1(bus1.getId())
+                .setConnectableBus2(bus2.getId())
+                .setBus1(bus1.getId())
+                .setBus2(bus2.getId())
+                .add();
+    }
+}

src/test/java/com/powsybl/nad/layout/LayoutParametersTest.java

@@ -18,10 +18,12 @@ class LayoutParametersTest {
     @Test
     void test() {
         LayoutParameters layoutParameters0 = new LayoutParameters()
-                .setTextNodesForceLayout(true);
+                .setTextNodesForceLayout(true)
+                .setSpringRepulsionFactorForceLayout(1.0);
 
         LayoutParameters layoutParameters1 = new LayoutParameters(layoutParameters0);
 
         assertEquals(layoutParameters0.isTextNodesForceLayout(), layoutParameters1.isTextNodesForceLayout());
+        assertEquals(layoutParameters0.getSpringRepulsionFactorForceLayout(), layoutParameters1.getSpringRepulsionFactorForceLayout());
     }
 }