Lineargradient for Line in javafx

Question

How can I use lineargradient for Line in Javafx?
I tried this:

LinearGradient lg = new LinearGradient(...);
line.setFill(lg);  
....

It doesn't work.

Answer 1

Use this

line.setStyle("-fx-background-color: linear-gradient(to right, #color_1, #color_2);");

Answer 2

Based on this answer, you need to specify the gradient on absolute coordinates.

Something like this will work for any given ones:

LinearGradient linearGradient = new LinearGradient(x1, y1, x2, y2, false, CycleMethod.REFLECT, new Stop(0,Color.RED),new Stop(1,Color.GREEN));
line.setStroke(linearGradient);

Based on this answer, you can create a simple app to test it how it works when you move the anchor nodes around the scene:

private final DoubleProperty x1 = new SimpleDoubleProperty();
public final double getX1() { return x1.get(); }
public final void setX1(double value) { x1.set(value); }
public final DoubleProperty x1Property() { return x1; }

private final DoubleProperty x2 = new SimpleDoubleProperty();
public final double getX2() { return x2.get(); }
public final void setX2(double value) { x2.set(value); }
public final DoubleProperty x2Property() { return x2; }

private final DoubleProperty y1 = new SimpleDoubleProperty();
public final double getY1() { return y1.get(); }
public final void setY1(double value) { y1.set(value); }
public final DoubleProperty y1Property() { return y1; }

private final DoubleProperty y2 = new SimpleDoubleProperty();
public final double getY2() { return y2.get(); }
public final void setY2(double value) { y2.set(value); }
public final DoubleProperty y2Property() { return y2; }

private Line line;

@Override
public void start(Stage primaryStage) {
    Group group = new Group();
    primaryStage.setScene(new Scene(group, 400, 400));

    x1.set(100);
    y1.set(50);
    x2.set(200);
    y2.set(300);

    line = new Line(x1.get(), y1.get(), x2.get(), y2.get());
    line.startXProperty().bind(x1);
    line.startYProperty().bind(y1);
    line.endXProperty().bind(x2);
    line.endYProperty().bind(y2);
    line.setStrokeWidth(12); 
    line.setMouseTransparent(true);

    Anchor start = new Anchor(Color.BLUE, x1, y1);
    Anchor end = new Anchor(Color.YELLOW, x2, y2);

    group.getChildren().setAll(line, start, end);

    x1Property().addListener(o -> updateLine());
    x2Property().addListener(o -> updateLine());
    y1Property().addListener(o -> updateLine());
    y2Property().addListener(o -> updateLine());
    updateLine();

    primaryStage.show();
}

private void updateLine() {
    LinearGradient linearGradient = new LinearGradient(x1.get(), y1.get(), x2.get(), y2.get(), false, CycleMethod.REFLECT, new Stop(0,Color.RED),new Stop(1,Color.GREEN));
    line.setStroke(linearGradient);
}

private class Anchor extends Circle { 

    Anchor(Color color, DoubleProperty x, DoubleProperty y) {
        super(x.get(), y.get(), 10);
        setFill(color.deriveColor(1, 1, 1, 0.5));
        setStroke(color);
        setStrokeWidth(2);
        setStrokeType(StrokeType.OUTSIDE);

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

    // make a node movable by dragging it around with the mouse.
    private void enableDrag() {
        final Delta dragDelta = new Delta();
        setOnMousePressed(mouseEvent -> {
            // record a delta distance for the drag and drop operation.
            dragDelta.x = getCenterX() - mouseEvent.getX();
            dragDelta.y = getCenterY() - mouseEvent.getY();
            getScene().setCursor(Cursor.MOVE);
        });
        setOnMouseReleased(mouseEvent -> {
            getScene().setCursor(Cursor.HAND);
        });
        setOnMouseDragged(mouseEvent -> {
            double newX = mouseEvent.getX() + dragDelta.x;
            if (newX > 0 && newX < getScene().getWidth()) {
                setCenterX(newX);
            }
            double newY = mouseEvent.getY() + dragDelta.y;
            if (newY > 0 && newY < getScene().getHeight()) {
                setCenterY(newY);
            }
        });
        setOnMouseEntered(mouseEvent -> {
            if (!mouseEvent.isPrimaryButtonDown()) {
                getScene().setCursor(Cursor.HAND);
            }
        });
        setOnMouseExited(mouseEvent -> {
            if (!mouseEvent.isPrimaryButtonDown()) {
                getScene().setCursor(Cursor.DEFAULT);
            }
        });
    }

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