fading in and fading out of an circle in javafx canvas - animation

Question

I would like to fade in and fadeout a circle in a javafx canvas.
I can move a circle from one part of the screen to another but i just can't seem to get this object to fade in and out.
Below is the code i used for moving a circle from one part of the screen to the other
public class AnimatedCircleOnCanvas extends Application {
public static final double W = 200; // canvas dimensions.
public static final double H = 200;
public static final double D = 20; // diameter.
#Override public void start(Stage stage) {
DoubleProperty x = new SimpleDoubleProperty();
DoubleProperty y = new SimpleDoubleProperty();
Timeline timeline = new Timeline(
new KeyFrame(Duration.seconds(0),
new KeyValue(x, 0),
new KeyValue(y, 0)
),
new KeyFrame(Duration.seconds(3),
new KeyValue(x, W - D),
new KeyValue(y, H - D)
)
);
timeline.setAutoReverse(true);
timeline.setCycleCount(Timeline.INDEFINITE);
final Canvas canvas = new Canvas(W, H);
AnimationTimer timer = new AnimationTimer() {
#Override
public void handle(long now) {
GraphicsContext gc = canvas.getGraphicsContext2D();
gc.setFill(Color.CORNSILK);
gc.fillRect(0, 0, W, H);
gc.setFill(Color.FORESTGREEN);
gc.fillOval(
x.doubleValue(),
y.doubleValue(),
D,
D
);
}
};
stage.setScene(
new Scene(
new Group(
canvas
)
)
);
stage.show();
timer.start();
timeline.play();
}
public static void main(String[] args) { launch(args); }
}
Your help is greatly appreciated

Answer 1

Animate a DoubleProperty for the opacity in values ranging from 1 to 0 in exactly the same way as you animated the properties for x and y, and then use Color.deriveColor(...) to set the color based on the changing property:
import javafx.animation.AnimationTimer;
import javafx.animation.KeyFrame;
import javafx.animation.KeyValue;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.beans.property.DoubleProperty;
import javafx.beans.property.SimpleDoubleProperty;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
import javafx.util.Duration;
public class FadeCircleOnCanvas extends Application {
public static final double W = 200; // canvas dimensions.
public static final double H = 200;
public static final double D = 20; // diameter.
#Override public void start(Stage stage) {
DoubleProperty opacity = new SimpleDoubleProperty();
Timeline timeline = new Timeline(
new KeyFrame(Duration.seconds(0),
new KeyValue(opacity, 1)
),
new KeyFrame(Duration.seconds(3),
new KeyValue(opacity, 0)
)
);
timeline.setAutoReverse(true);
timeline.setCycleCount(Timeline.INDEFINITE);
final Canvas canvas = new Canvas(W, H);
AnimationTimer timer = new AnimationTimer() {
#Override
public void handle(long now) {
GraphicsContext gc = canvas.getGraphicsContext2D();
gc.setFill(Color.CORNSILK);
gc.fillRect(0, 0, W, H);
gc.setFill(Color.FORESTGREEN.deriveColor(0, 1, 1, opacity.get()));
gc.fillOval(
W/2,
H/2,
D,
D
);
}
};
stage.setScene(
new Scene(
new Group(
canvas
)
)
);
stage.show();
timer.start();
timeline.play();
}
public static void main(String[] args) { launch(args); }
}
In general, I prefer not to use a Canvas for this, and just to use Shape instances placed in a Pane. Then you can directly change the pre-defined properties of the Shape, or in many cases use specific pre-defined animations (TranslateTransition or FadeTransition for example).
Here's the same example using this technique:
import javafx.animation.FadeTransition;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;
import javafx.util.Duration;
public class FadeCircleOnCanvas extends Application {
public static final double W = 200; // canvas dimensions.
public static final double H = 200;
public static final double D = 20; // diameter.
#Override public void start(Stage stage) {
Circle circle = new Circle(W/2, H/2, D, Color.FORESTGREEN);
FadeTransition fade = new FadeTransition(Duration.seconds(3), circle);
fade.setFromValue(1);
fade.setToValue(0);
fade.setAutoReverse(true);
fade.setCycleCount(Timeline.INDEFINITE);
Pane pane = new Pane(circle);
stage.setScene(
new Scene(
pane, W, H, Color.CORNSILK
)
);
stage.show();
fade.play();
}
public static void main(String[] args) { launch(args); }
}