Demo for understanding JavaFX Layout Bounds

## BoundsPlayground.java
import javafx.application.Application;
import javafx.beans.property.DoubleProperty;
import javafx.beans.property.ObjectProperty;
import javafx.beans.property.ReadOnlyObjectProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.EventHandler;
import javafx.geometry.Bounds;
import javafx.scene.Cursor;
import javafx.scene.Group;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.effect.DropShadow;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.StackPane;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.*;
import javafx.scene.web.WebView;
import javafx.stage.Stage;
import javafx.stage.StageStyle;
import javafx.stage.WindowEvent;

/** Demo for understanding JavaFX Layout Bounds */
public class BoundsPlayground extends Application {
  final ObservableList<Shape>     shapes        = FXCollections.observableArrayList();
  final ObservableList<ShapePair> intersections = FXCollections.observableArrayList();

  ObjectProperty<BoundsType> selectedBoundsType = new SimpleObjectProperty<BoundsType>(BoundsType.LAYOUT_BOUNDS);

  public static void main(String[] args) { launch(args); }
  @Override public void start(Stage stage) {
    stage.setTitle("Bounds Playground");

    // define some objects to manipulate on the scene.
    Circle greenCircle = new Circle(100, 100, 50, Color.FORESTGREEN); greenCircle.setId("Green Circle");
    Circle redCircle   = new Circle(300, 200, 50, Color.FIREBRICK);   redCircle.setId("Red Circle");

    Line line = new Line(25, 300, 375, 200); line.setId("Line");
    line.setStrokeLineCap(StrokeLineCap.ROUND);
    line.setStroke(Color.MIDNIGHTBLUE);
    line.setStrokeWidth(5);

    final Anchor anchor1 = new Anchor("Anchor 1", line.startXProperty(), line.startYProperty());
    final Anchor anchor2 = new Anchor("Anchor 2", line.endXProperty(),   line.endYProperty());

    final Group group = new Group(greenCircle, redCircle, line, anchor1, anchor2);

    // monitor intersections of shapes in the scene.
    for (Node node : group.getChildrenUnmodifiable()) {
      if (node instanceof Shape) {
        shapes.add((Shape) node);
      }
    }
    testIntersections();

    // enable dragging for the scene objects.
    Circle[] circles = { greenCircle, redCircle, anchor1, anchor2 };
    for (Circle circle : circles) {
      enableDrag(circle);
      circle.centerXProperty().addListener(new ChangeListener<Number>() {
        @Override public void changed(ObservableValue<? extends Number> observableValue, Number oldValue, Number newValue) {
          testIntersections();
        }
      });
      circle.centerYProperty().addListener(new ChangeListener<Number>() {
        @Override public void changed(ObservableValue<? extends Number> observableValue, Number oldValue, Number newValue) {
          testIntersections();
        }
      });
    }

    // define an overlay to show the layout bounds of the scene's shapes.
    Group layoutBoundsOverlay = new Group();
    layoutBoundsOverlay.setMouseTransparent(true);
    for (Shape shape : shapes) {
      if (!(shape instanceof Anchor)) {
        layoutBoundsOverlay.getChildren().add(new BoundsDisplay(shape));
      }
    }

    // layout the scene.
    final StackPane background = new StackPane();
    background.setStyle("-fx-background-color: cornsilk;");
    final Scene scene = new Scene(new Group(background, group, layoutBoundsOverlay), 600, 500);
    background.prefHeightProperty().bind(scene.heightProperty());
    background.prefWidthProperty().bind(scene.widthProperty());
    stage.setScene(scene);
    stage.show();

    createUtilityWindow(stage, layoutBoundsOverlay, new Shape[] { greenCircle, redCircle });
  }

  // update the list of intersections.
  private void testIntersections() {
    intersections.clear();

    // for each shape test it's intersection with all other shapes.
    for (Shape src : shapes) {
      for (Shape dest : shapes) {
        ShapePair pair = new ShapePair(src, dest);
        if ((!(pair.a instanceof Anchor) && !(pair.b instanceof Anchor))
            && !intersections.contains(pair)
            && pair.intersects(selectedBoundsType.get())) {
          intersections.add(pair);
        }
      }
    }
  }

  // make a node movable by dragging it around with the mouse.
  private void enableDrag(final Circle circle) {
    final Delta dragDelta = new Delta();
    circle.setOnMousePressed(new EventHandler<MouseEvent>() {
      @Override public void handle(MouseEvent mouseEvent) {
        // record a delta distance for the drag and drop operation.
        dragDelta.x = circle.getCenterX() - mouseEvent.getX();
        dragDelta.y = circle.getCenterY() - mouseEvent.getY();
        circle.getScene().setCursor(Cursor.MOVE);
      }
    });
    circle.setOnMouseReleased(new EventHandler<MouseEvent>() {
      @Override public void handle(MouseEvent mouseEvent) {
        circle.getScene().setCursor(Cursor.HAND);
      }
    });
    circle.setOnMouseDragged(new EventHandler<MouseEvent>() {
      @Override public void handle(MouseEvent mouseEvent) {
        circle.setCenterX(mouseEvent.getX() + dragDelta.x);
        circle.setCenterY(mouseEvent.getY() + dragDelta.y);
      }
    });
    circle.setOnMouseEntered(new EventHandler<MouseEvent>() {
      @Override public void handle(MouseEvent mouseEvent) {
        if (!mouseEvent.isPrimaryButtonDown()) {
          circle.getScene().setCursor(Cursor.HAND);
        }
      }
    });
    circle.setOnMouseExited(new EventHandler<MouseEvent>() {
      @Override public void handle(MouseEvent mouseEvent) {
        if (!mouseEvent.isPrimaryButtonDown()) {
          circle.getScene().setCursor(Cursor.DEFAULT);
        }
      }
    });
  }

  // a helper enumeration of the various types of bounds we can work with.
  enum BoundsType { LAYOUT_BOUNDS, BOUNDS_IN_LOCAL, BOUNDS_IN_PARENT }

  // a translucent overlay display rectangle to show the bounds of a Shape.
  class BoundsDisplay extends Rectangle {
    // the shape to which the bounds display has been type.
    final Shape monitoredShape;
    private ChangeListener<Bounds> boundsChangeListener;

    BoundsDisplay(final Shape shape) {
      setFill(Color.LIGHTGRAY.deriveColor(1, 1, 1, 0.35));
      setStroke(Color.LIGHTGRAY.deriveColor(1, 1, 1, 0.5));
      setStrokeType(StrokeType.INSIDE);
      setStrokeWidth(3);

      monitoredShape = shape;

      monitorBounds(BoundsType.LAYOUT_BOUNDS);
    }

    // set the type of the shape's bounds to monitor for the bounds display.
    void monitorBounds(final BoundsType boundsType) {
      // remove the shape's previous boundsType.
      if (boundsChangeListener != null) {
        final ReadOnlyObjectProperty<Bounds> oldBounds;
        switch (selectedBoundsType.get()) {
          case LAYOUT_BOUNDS:    oldBounds = monitoredShape.layoutBoundsProperty();   break;
          case BOUNDS_IN_LOCAL:  oldBounds = monitoredShape.boundsInLocalProperty();  break;
          case BOUNDS_IN_PARENT: oldBounds = monitoredShape.boundsInParentProperty(); break;
          default: oldBounds = null;
        }
        if (oldBounds != null) {
          oldBounds.removeListener(boundsChangeListener);
        }
      }

      // determine the shape's bounds for the given boundsType.
      final ReadOnlyObjectProperty<Bounds> bounds;
      switch (boundsType) {
        case LAYOUT_BOUNDS:    bounds = monitoredShape.layoutBoundsProperty();   break;
        case BOUNDS_IN_LOCAL:  bounds = monitoredShape.boundsInLocalProperty();  break;
        case BOUNDS_IN_PARENT: bounds = monitoredShape.boundsInParentProperty(); break;
        default: bounds = null;
      }

      // set the visual bounds display based upon the new bounds and keep it in sync.
      updateBoundsDisplay(bounds.get());

      // keep the visual bounds display based upon the new bounds and keep it in sync.
      boundsChangeListener = new ChangeListener<Bounds>() {
        @Override public void changed(ObservableValue<? extends Bounds> observableValue, Bounds oldBounds, Bounds newBounds) {
          updateBoundsDisplay(newBounds);
        }
      };
      bounds.addListener(boundsChangeListener);
    }

    // update this bounds display to match a new set of bounds.
    private void updateBoundsDisplay(Bounds newBounds) {
      setX(newBounds.getMinX());
      setY(newBounds.getMinY());
      setWidth(newBounds.getWidth());
      setHeight(newBounds.getHeight());
    }
  }

  // an anchor displayed around a point.
  class Anchor extends Circle {
    Anchor(String id, DoubleProperty x, DoubleProperty y) {
      super(x.get(), y.get(), 10);
      setId(id);
      setFill(Color.GOLD.deriveColor(1, 1, 1, 0.5));
      setStroke(Color.GOLD);
      setStrokeWidth(2);
      setStrokeType(StrokeType.OUTSIDE);

      x.bind(centerXProperty());
      y.bind(centerYProperty());
    }
  }

  // records relative x and y co-ordinates.
  class Delta { double x, y; }

  // records a pair of (possibly) intersecting shapes.
  class ShapePair {
    private Shape a, b;
    public ShapePair(Shape src, Shape dest) {
      this.a = src; this.b = dest;
    }

    public boolean intersects(BoundsType boundsType) {
      if (a == b) return false;

      a.intersects(b.getBoundsInLocal());
      switch (boundsType) {
        case LAYOUT_BOUNDS:    return a.getLayoutBounds().intersects(b.getLayoutBounds());
        case BOUNDS_IN_LOCAL:  return a.getBoundsInLocal().intersects(b.getBoundsInLocal());
        case BOUNDS_IN_PARENT: return a.getBoundsInParent().intersects(b.getBoundsInParent());
        default: return false;
      }
    }

    @Override public String toString() {
      return a.getId() + " : " + b.getId();
    }

    @Override
    public boolean equals(Object other) {
      ShapePair o = (ShapePair) other;
      return o != null && ((a == o.a && b == o.b) || (a == o.b) &&  (b == o.a));
    }

    @Override
    public int hashCode() {
      int result = a != null ? a.hashCode() : 0;
      result = 31 * result + (b != null ? b.hashCode() : 0);
      return result;
    }
  }

  // define a utility stage for reporting intersections.
  private void createUtilityWindow(Stage stage, final Group boundsOverlay, final Shape[] transformableShapes) {
    final Stage reportingStage = new Stage();
    reportingStage.setTitle("Control Panel");
    reportingStage.initStyle(StageStyle.UTILITY);
    reportingStage.setX(stage.getX() + stage.getWidth());
    reportingStage.setY(stage.getY());

    // define content for the intersections utility panel.
    final ListView<ShapePair> intersectionView = new ListView<ShapePair>(intersections);
    final Label instructions = new Label(
      "Click on any circle in the scene to the left to drag it around."
    );
    instructions.setMinSize(Control.USE_PREF_SIZE, Control.USE_PREF_SIZE);
    instructions.setStyle("-fx-font-weight: bold; -fx-text-fill: darkgreen;");

    final Label intersectionInstructions = new Label(
      "Any intersecting bounds in the scene will be reported below."
    );
    instructions.setMinSize(Control.USE_PREF_SIZE, Control.USE_PREF_SIZE);

    // add the ability to set a translate value for the circles.
    final CheckBox translateNodes = new CheckBox("Translate circles");
    translateNodes.selectedProperty().addListener(new ChangeListener<Boolean>() {
      @Override public void changed(ObservableValue<? extends Boolean> observableValue, Boolean oldValue, Boolean doTranslate) {
        if (doTranslate) {
          for (Shape shape : transformableShapes) {
            shape.setTranslateY(100);
            testIntersections();
          }
        } else {
          for (Shape shape : transformableShapes) {
            shape.setTranslateY(0);
            testIntersections();
          }
        }
      }
    });
    translateNodes.selectedProperty().set(false);

    // add the ability to add an effect to the circles.
    final Label modifyInstructions = new Label(
      "Modify visual display aspects."
    );
    modifyInstructions.setStyle("-fx-font-weight: bold;");
    modifyInstructions.setMinSize(Control.USE_PREF_SIZE, Control.USE_PREF_SIZE);
    final CheckBox effectNodes = new CheckBox("Add an effect to circles");
    effectNodes.selectedProperty().addListener(new ChangeListener<Boolean>() {
      @Override public void changed(ObservableValue<? extends Boolean> observableValue, Boolean oldValue, Boolean doTranslate) {
        if (doTranslate) {
          for (Shape shape : transformableShapes) {
            shape.setEffect(new DropShadow());
            testIntersections();
          }
        } else {
          for (Shape shape : transformableShapes) {
            shape.setEffect(null);
            testIntersections();
          }
        }
      }
    });
    effectNodes.selectedProperty().set(true);

    // add the ability to add a stroke to the circles.
    final CheckBox strokeNodes = new CheckBox("Add outside strokes to circles");
    strokeNodes.selectedProperty().addListener(new ChangeListener<Boolean>() {
      @Override public void changed(ObservableValue<? extends Boolean> observableValue, Boolean oldValue, Boolean doTranslate) {
        if (doTranslate) {
          for (Shape shape : transformableShapes) {
            shape.setStroke(Color.LIGHTSEAGREEN);
            shape.setStrokeWidth(10);
            testIntersections();
          }
        } else {
          for (Shape shape : transformableShapes) {
            shape.setStrokeWidth(0);
            testIntersections();
          }
        }
      }
    });
    strokeNodes.selectedProperty().set(true);

    // add the ability to show or hide the layout bounds overlay.
    final Label showBoundsInstructions = new Label(
      "The gray squares represent layout bounds."
    );
    showBoundsInstructions.setStyle("-fx-font-weight: bold;");
    showBoundsInstructions.setMinSize(Control.USE_PREF_SIZE, Control.USE_PREF_SIZE);
    final CheckBox showBounds = new CheckBox("Show Bounds");
    boundsOverlay.visibleProperty().bind(showBounds.selectedProperty());
    showBounds.selectedProperty().set(true);

    // create a container for the display control checkboxes.
    VBox displayChecks = new VBox(10);
    displayChecks.getChildren().addAll(modifyInstructions, translateNodes, effectNodes, strokeNodes, showBoundsInstructions, showBounds);

    // create a toggle group for the bounds type to use.
    ToggleGroup boundsToggleGroup = new ToggleGroup();
    final RadioButton useLayoutBounds   = new RadioButton("Use Layout Bounds");
    final RadioButton useBoundsInLocal  = new RadioButton("Use Bounds in Local");
    final RadioButton useBoundsInParent = new RadioButton("Use Bounds in Parent");
    useLayoutBounds.setToggleGroup(boundsToggleGroup);
    useBoundsInLocal.setToggleGroup(boundsToggleGroup);
    useBoundsInParent.setToggleGroup(boundsToggleGroup);
    VBox boundsToggles = new VBox(10);
    boundsToggles.getChildren().addAll(useLayoutBounds, useBoundsInLocal, useBoundsInParent);

    // change the layout bounds display depending on which bounds type has been selected.
    useLayoutBounds.selectedProperty().addListener(new ChangeListener<Boolean>() {
      @Override public void changed(ObservableValue<? extends Boolean> observableValue, Boolean aBoolean, Boolean isSelected) {
        if (isSelected) {
          for (Node overlay : boundsOverlay.getChildren()) {
            ((BoundsDisplay) overlay).monitorBounds(BoundsType.LAYOUT_BOUNDS);
          }
          selectedBoundsType.set(BoundsType.LAYOUT_BOUNDS);
          testIntersections();
        }
      }
    });
    useBoundsInLocal.selectedProperty().addListener(new ChangeListener<Boolean>() {
      @Override public void changed(ObservableValue<? extends Boolean> observableValue, Boolean aBoolean, Boolean isSelected) {
        if (isSelected) {
          for (Node overlay : boundsOverlay.getChildren()) {
            ((BoundsDisplay) overlay).monitorBounds(BoundsType.BOUNDS_IN_LOCAL);
          }
          selectedBoundsType.set(BoundsType.BOUNDS_IN_LOCAL);
          testIntersections();
        }
      }
    });
    useBoundsInParent.selectedProperty().addListener(new ChangeListener<Boolean>() {
      @Override public void changed(ObservableValue<? extends Boolean> observableValue, Boolean aBoolean, Boolean isSelected) {
        if (isSelected) {
          for (Node overlay : boundsOverlay.getChildren()) {
            ((BoundsDisplay) overlay).monitorBounds(BoundsType.BOUNDS_IN_PARENT);
          }
          selectedBoundsType.set(BoundsType.BOUNDS_IN_PARENT);
          testIntersections();
        }
      }
    });
    useLayoutBounds.selectedProperty().set(true);

    WebView boundsExplanation = new WebView();
    boundsExplanation.getEngine().loadContent(
      "<html><body bgcolor='darkseagreen' fgcolor='lightgrey' style='font-size:12px'><dl>" +
      "<dt><b>Layout Bounds</b></dt><dd>The boundary of the shape.</dd><br/>" +
      "<dt><b>Bounds in Local</b></dt><dd>The boundary of the shape and effect.</dd><br/>" +
      "<dt><b>Bounds in Parent</b></dt><dd>The boundary of the shape, effect and transforms.<br/>The co-ordinates of what you see.</dd>" +
      "</dl></body></html>"
    );
    boundsExplanation.setPrefWidth(100);
    boundsExplanation.setMinHeight(130);
    boundsExplanation.setMaxHeight(130);
    boundsExplanation.setStyle("-fx-background-color: transparent");

    // layout the utility pane.
    VBox utilityLayout = new VBox(10);
    utilityLayout.setStyle("-fx-padding:10; -fx-background-color: linear-gradient(to bottom, lightblue, derive(lightblue, 20%));");
    utilityLayout.getChildren().addAll(instructions, intersectionInstructions, intersectionView, displayChecks, boundsToggles, boundsExplanation);
    utilityLayout.setPrefHeight(530);
    reportingStage.setScene(new Scene(utilityLayout));
    reportingStage.show();

    // ensure the utility window closes when the main app window closes.
    stage.setOnCloseRequest(new EventHandler<WindowEvent>() {
      @Override public void handle(WindowEvent windowEvent) {
        reportingStage.close();
      }
    });
  }
}