JavaFX 8 - Zooming Relative to Mouse Pointer

Question

I have been trying to use this example to learn about zooming and scaling. It does a great job of demonstrating scaling.

I\'ve been trying to figure out how to chan

Answer 1

Try this if you want to zoom a pane in a window. Call method on an event.

private void zoomIn(Pane pane) {
    Scale newScale = new Scale();
    newScale.setX(pane.getScaleX() + YOUR_ZOOM_FACTOR_VALUE);
    newScale.setY(pane.getScaleY() + YOUR_ZOOM_FACTOR_VALUE);
    newScale.setPivotX(pane.getScaleX());
    newScale.setPivotY(pane.getScaleY());
    pane.getTransforms().add(newScale);
}

Answer 2

I had the same question here on StackOverflow. The following code is a modified version of the question/answer there.

You can use

• right mouse button = panning
• left mouse button = dragging of the nodes
• scroll wheel = zoom in on mouse cursor location

The relevant part for you is the onScrollEventHandler.

import javafx.application.Application;
import javafx.beans.property.DoubleProperty;
import javafx.beans.property.SimpleDoubleProperty;
import javafx.event.EventHandler;
import javafx.scene.Group;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.control.Label;
import javafx.scene.input.MouseEvent;
import javafx.scene.input.ScrollEvent;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;

class PannableCanvas extends Pane {

    DoubleProperty myScale = new SimpleDoubleProperty(1.0);

    public PannableCanvas() {
        setPrefSize(600, 600);
        setStyle("-fx-background-color: lightgrey; -fx-border-color: blue;");

        // add scale transform
        scaleXProperty().bind(myScale);
        scaleYProperty().bind(myScale);
    }

    /**
     * Add a grid to the canvas, send it to back
     */
    public void addGrid() {

        double w = getBoundsInLocal().getWidth();
        double h = getBoundsInLocal().getHeight();

        // add grid
        Canvas grid = new Canvas(w, h);

        // don't catch mouse events
        grid.setMouseTransparent(true);

        GraphicsContext gc = grid.getGraphicsContext2D();

        gc.setStroke(Color.GRAY);
        gc.setLineWidth(1);

        // draw grid lines
        double offset = 50;
        for( double i=offset; i < w; i+=offset) {
            gc.strokeLine( i, 0, i, h);
            gc.strokeLine( 0, i, w, i);
        }

        getChildren().add( grid);

        grid.toBack();
    }

    public double getScale() {
        return myScale.get();
    }

    public void setScale( double scale) {
        myScale.set(scale);
    }

    public void setPivot( double x, double y) {
        setTranslateX(getTranslateX()-x);
        setTranslateY(getTranslateY()-y);
    }
}


/**
 * Mouse drag context used for scene and nodes.
 */
class DragContext {

    double mouseAnchorX;
    double mouseAnchorY;

    double translateAnchorX;
    double translateAnchorY;

}

/**
 * Listeners for making the nodes draggable via left mouse button. Considers if parent is zoomed.
 */
class NodeGestures {

    private DragContext nodeDragContext = new DragContext();

    PannableCanvas canvas;

    public NodeGestures( PannableCanvas canvas) {
        this.canvas = canvas;

    }

    public EventHandler<MouseEvent> getOnMousePressedEventHandler() {
        return onMousePressedEventHandler;
    }

    public EventHandler<MouseEvent> getOnMouseDraggedEventHandler() {
        return onMouseDraggedEventHandler;
    }

    private EventHandler<MouseEvent> onMousePressedEventHandler = new EventHandler<MouseEvent>() {

        public void handle(MouseEvent event) {

            // left mouse button => dragging
            if( !event.isPrimaryButtonDown())
                return;

            nodeDragContext.mouseAnchorX = event.getSceneX();
            nodeDragContext.mouseAnchorY = event.getSceneY();

            Node node = (Node) event.getSource();

            nodeDragContext.translateAnchorX = node.getTranslateX();
            nodeDragContext.translateAnchorY = node.getTranslateY();

        }

    };

    private EventHandler<MouseEvent> onMouseDraggedEventHandler = new EventHandler<MouseEvent>() {
        public void handle(MouseEvent event) {

            // left mouse button => dragging
            if( !event.isPrimaryButtonDown())
                return;

            double scale = canvas.getScale();

            Node node = (Node) event.getSource();

            node.setTranslateX(nodeDragContext.translateAnchorX + (( event.getSceneX() - nodeDragContext.mouseAnchorX) / scale));
            node.setTranslateY(nodeDragContext.translateAnchorY + (( event.getSceneY() - nodeDragContext.mouseAnchorY) / scale));

            event.consume();

        }
    };
}

/**
 * Listeners for making the scene's canvas draggable and zoomable
 */
class SceneGestures {

    private static final double MAX_SCALE = 10.0d;
    private static final double MIN_SCALE = .1d;

    private DragContext sceneDragContext = new DragContext();

    PannableCanvas canvas;

    public SceneGestures( PannableCanvas canvas) {
        this.canvas = canvas;
    }

    public EventHandler<MouseEvent> getOnMousePressedEventHandler() {
        return onMousePressedEventHandler;
    }

    public EventHandler<MouseEvent> getOnMouseDraggedEventHandler() {
        return onMouseDraggedEventHandler;
    }

    public EventHandler<ScrollEvent> getOnScrollEventHandler() {
        return onScrollEventHandler;
    }

    private EventHandler<MouseEvent> onMousePressedEventHandler = new EventHandler<MouseEvent>() {

        public void handle(MouseEvent event) {

            // right mouse button => panning
            if( !event.isSecondaryButtonDown())
                return;

            sceneDragContext.mouseAnchorX = event.getSceneX();
            sceneDragContext.mouseAnchorY = event.getSceneY();

            sceneDragContext.translateAnchorX = canvas.getTranslateX();
            sceneDragContext.translateAnchorY = canvas.getTranslateY();

        }

    };

    private EventHandler<MouseEvent> onMouseDraggedEventHandler = new EventHandler<MouseEvent>() {
        public void handle(MouseEvent event) {

            // right mouse button => panning
            if( !event.isSecondaryButtonDown())
                return;

            canvas.setTranslateX(sceneDragContext.translateAnchorX + event.getSceneX() - sceneDragContext.mouseAnchorX);
            canvas.setTranslateY(sceneDragContext.translateAnchorY + event.getSceneY() - sceneDragContext.mouseAnchorY);

            event.consume();
        }
    };

    /**
     * Mouse wheel handler: zoom to pivot point
     */
    private EventHandler<ScrollEvent> onScrollEventHandler = new EventHandler<ScrollEvent>() {

        @Override
        public void handle(ScrollEvent event) {

            double delta = 1.2;

            double scale = canvas.getScale(); // currently we only use Y, same value is used for X
            double oldScale = scale;

            if (event.getDeltaY() < 0)
                scale /= delta;
            else
                scale *= delta;

            scale = clamp( scale, MIN_SCALE, MAX_SCALE);

            double f = (scale / oldScale)-1;

            double dx = (event.getSceneX() - (canvas.getBoundsInParent().getWidth()/2 + canvas.getBoundsInParent().getMinX()));
            double dy = (event.getSceneY() - (canvas.getBoundsInParent().getHeight()/2 + canvas.getBoundsInParent().getMinY()));

            canvas.setScale( scale);

            // note: pivot value must be untransformed, i. e. without scaling
            canvas.setPivot(f*dx, f*dy);

            event.consume();

        }

    };


    public static double clamp( double value, double min, double max) {

        if( Double.compare(value, min) < 0)
            return min;

        if( Double.compare(value, max) > 0)
            return max;

        return value;
    }
}



/**
 * An application with a zoomable and pannable canvas.
 */
public class ZoomAndScrollApplication extends Application {
    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage stage) {

        Group group = new Group();

        // create canvas
        PannableCanvas canvas = new PannableCanvas();

        // we don't want the canvas on the top/left in this example => just
        // translate it a bit
        canvas.setTranslateX(100);
        canvas.setTranslateY(100);

        // create sample nodes which can be dragged
        NodeGestures nodeGestures = new NodeGestures( canvas);

        Label label1 = new Label("Draggable node 1");
        label1.setTranslateX(10);
        label1.setTranslateY(10);
        label1.addEventFilter( MouseEvent.MOUSE_PRESSED, nodeGestures.getOnMousePressedEventHandler());
        label1.addEventFilter( MouseEvent.MOUSE_DRAGGED, nodeGestures.getOnMouseDraggedEventHandler());

        Label label2 = new Label("Draggable node 2");
        label2.setTranslateX(100);
        label2.setTranslateY(100);
        label2.addEventFilter( MouseEvent.MOUSE_PRESSED, nodeGestures.getOnMousePressedEventHandler());
        label2.addEventFilter( MouseEvent.MOUSE_DRAGGED, nodeGestures.getOnMouseDraggedEventHandler());

        Label label3 = new Label("Draggable node 3");
        label3.setTranslateX(200);
        label3.setTranslateY(200);
        label3.addEventFilter( MouseEvent.MOUSE_PRESSED, nodeGestures.getOnMousePressedEventHandler());
        label3.addEventFilter( MouseEvent.MOUSE_DRAGGED, nodeGestures.getOnMouseDraggedEventHandler());

        Circle circle1 = new Circle( 300, 300, 50);
        circle1.setStroke(Color.ORANGE);
        circle1.setFill(Color.ORANGE.deriveColor(1, 1, 1, 0.5));
        circle1.addEventFilter( MouseEvent.MOUSE_PRESSED, nodeGestures.getOnMousePressedEventHandler());
        circle1.addEventFilter( MouseEvent.MOUSE_DRAGGED, nodeGestures.getOnMouseDraggedEventHandler());

        Rectangle rect1 = new Rectangle(100,100);
        rect1.setTranslateX(450);
        rect1.setTranslateY(450);
        rect1.setStroke(Color.BLUE);
        rect1.setFill(Color.BLUE.deriveColor(1, 1, 1, 0.5));
        rect1.addEventFilter( MouseEvent.MOUSE_PRESSED, nodeGestures.getOnMousePressedEventHandler());
        rect1.addEventFilter( MouseEvent.MOUSE_DRAGGED, nodeGestures.getOnMouseDraggedEventHandler());

        canvas.getChildren().addAll(label1, label2, label3, circle1, rect1);

        group.getChildren().add(canvas);

        // create scene which can be dragged and zoomed
        Scene scene = new Scene(group, 1024, 768);

        SceneGestures sceneGestures = new SceneGestures(canvas);
        scene.addEventFilter( MouseEvent.MOUSE_PRESSED, sceneGestures.getOnMousePressedEventHandler());
        scene.addEventFilter( MouseEvent.MOUSE_DRAGGED, sceneGestures.getOnMouseDraggedEventHandler());
        scene.addEventFilter( ScrollEvent.ANY, sceneGestures.getOnScrollEventHandler());

        stage.setScene(scene);
        stage.show();

        canvas.addGrid();

    }
}

Answer 3

I've had this exact problem, I'll show my (heavily condensed) solution. First create a class that is in charge of the zooming:

public class AnimatedZoomOperator {

    private Timeline timeline;

    public AnimatedZoomOperator() {         
         this.timeline = new Timeline(60);
    }

    public void zoom(Node node, double factor, double x, double y) {    
        // determine scale
        double oldScale = node.getScaleX();
        double scale = oldScale * factor;
        double f = (scale / oldScale) - 1;

        // determine offset that we will have to move the node
        Bounds bounds = node.localToScene(node.getBoundsInLocal());
        double dx = (x - (bounds.getWidth() / 2 + bounds.getMinX()));
        double dy = (y - (bounds.getHeight() / 2 + bounds.getMinY()));

        // timeline that scales and moves the node
        timeline.getKeyFrames().clear();
        timeline.getKeyFrames().addAll(
            new KeyFrame(Duration.millis(200), new KeyValue(node.translateXProperty(), node.getTranslateX() - f * dx)),
            new KeyFrame(Duration.millis(200), new KeyValue(node.translateYProperty(), node.getTranslateY() - f * dy)),
            new KeyFrame(Duration.millis(200), new KeyValue(node.scaleXProperty(), scale)),
            new KeyFrame(Duration.millis(200), new KeyValue(node.scaleYProperty(), scale))
        );
        timeline.play();
    }
}

Note that this uses a timeline to animate the zoom. If you don't want this, you can call node.setTranslateX(...), node.setScaleX(...), etc. directly.

Now to use this operator you can do something like this:

// Create panel
StackPane zoomPane = new StackPane();
zoomPane.getChildren().add(new Circle(100, 100, 10));
zoomPane.getChildren().add(new Circle(200, 200, 20));

// Create operator
AnimatedZoomOperator zoomOperator = new AnimatedZoomOperator();

// Listen to scroll events (similarly you could listen to a button click, slider, ...)
zoomPane.setOnScroll(new EventHandler<ScrollEvent>() {
    @Override
    public void handle(ScrollEvent event) {
        double zoomFactor = 1.5;
        if (event.getDeltaY() <= 0) {
            // zoom out
            zoomFactor = 1 / zoomFactor;
        }
        zoomOperator.zoom(zoomPane, zoomFactor, event.getSceneX(), event.getSceneY());
    }
});