Fade Effect with JavaFX

Question

Im trying to realize a special FadeTransition effect. But I have no idea how I can manage it. For some node I would like to increase the opacity from left to right (for example in Powerpoint, you can change the slides with such an effect). Here is an easy example for rectangles. But the second one should fadeIn from left to right (the opacity should increase on the left side earlier as on the right side). With timeline and KeyValues/KeyFrames I found also no solution. Thanks in advance.

Rectangle rec2;

@Override
public void start(Stage stage) {
    Group root = new Group();
    Scene scene = new Scene(root, 400, 300, Color.BLACK);
    stage.setTitle("JavaFX Scene Graph Demo");       

    Pane pane = new Pane();
    Button btnForward = new Button();
    btnForward.setText(">");
    btnForward.setOnAction(new EventHandler<ActionEvent>() {
        @Override
        public void handle(ActionEvent event) {
            FadeTransition ft = new FadeTransition(Duration.millis(2000), rec2);
            ft.setFromValue(0.);
            ft.setToValue(1.);
            ft.play();
        }
    });        
    Rectangle rec1 = new Rectangle(0, 0, 300,200);        
    rec1.setFill(Color.RED);
    rec2 = new Rectangle(100, 50, 100,100);        
    rec2.setFill(Color.GREEN);
    rec2.setOpacity(0.);
    pane.getChildren().addAll(rec1,rec2);
    root.getChildren().add(pane);
    root.getChildren().add(btnForward);
    stage.setScene(scene);
    stage.show();
}

Answer 1

Define the fill of the rectangle using css with a linear gradient which references looked-up colors for the left and right edges of the rectangle. (This can be inline or in an external style sheet.)

Define a couple of DoublePropertys representing the opacities of the left and right edge.

Define the looked-up colors on the rectangle or one of its parents using an inline style bound to the two double properties.

Use a timeline to change the values of the opacity properties.

import javafx.animation.KeyFrame;
import javafx.animation.KeyValue;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.beans.property.DoubleProperty;
import javafx.beans.property.SimpleDoubleProperty;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;
import javafx.util.Duration;

public class FadeInRectangle extends Application {

    @Override
    public void start(Stage primaryStage) {
        Group root = new Group();
        Scene scene = new Scene(root, 400, 300, Color.BLACK);
        primaryStage.setTitle("JavaFX Scene Graph Demo");       

        Pane pane = new Pane();
        Rectangle rec1 = new Rectangle(0, 0, 300,200);        
        rec1.setFill(Color.RED);
        Rectangle rec2 = new Rectangle(100, 50, 100,100);

        rec2.setStyle("-fx-fill: linear-gradient(to right, left-col, right-col);");

        final DoubleProperty leftEdgeOpacity = new SimpleDoubleProperty(0);
        final DoubleProperty rightEdgeOpacity = new SimpleDoubleProperty(0);

        root.styleProperty().bind(
            Bindings.format("left-col: rgba(0,128,0,%f); right-col: rgba(0,128,0,%f);", leftEdgeOpacity, rightEdgeOpacity)   
        );

        Button btnForward = new Button();
        btnForward.setText(">");
        btnForward.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                Timeline timeline = new Timeline(
                    new KeyFrame(Duration.ZERO, new KeyValue(leftEdgeOpacity, 0)),
                    new KeyFrame(Duration.ZERO, new KeyValue(rightEdgeOpacity, 0)),
                    new KeyFrame(Duration.millis(500), new KeyValue(rightEdgeOpacity, 0)),
                    new KeyFrame(Duration.millis(1500), new KeyValue(leftEdgeOpacity, 1)),
                    new KeyFrame(Duration.millis(2000), new KeyValue(rightEdgeOpacity, 1)),
                    new KeyFrame(Duration.millis(2000), new KeyValue(leftEdgeOpacity, 1))
                );
                timeline.play();
            }
        });        
        pane.getChildren().addAll(rec1,rec2);
        root.getChildren().add(pane);
        root.getChildren().add(btnForward);
        primaryStage.setScene(scene);
        primaryStage.show();

    }

    public static void main(String[] args) {
        launch(args);
    }
}