JavaFX - Zoom relative to mouse position


Question

I can't get working zoom relative to mouse position in JavaFX. I've read and tried rewrite this and this, but it's not working. Can't scroll viewport using scrollPane.setViewportBounds(). I must use scrollPane.setHvalue() and scrollPane.setVvalue(), but can't get right recalculation to keep the same pixels under the mouse cursor. Current code keeps scrollbars positions:

ZoomHandler.java

import javafx.event.EventHandler;
import javafx.scene.control.ScrollPane;
import javafx.scene.input.ScrollEvent;
import javafx.scene.layout.Pane;

public class ZoomHandler implements EventHandler<ScrollEvent> {

    private final ScrollPane scrollPane;
    private final Pane canvas;    
    private final double minScale;
    private final double maxScale;

    public ZoomHandler(ScrollPane scrollPane, Pane canvas, double minScale, double maxScale) {
        this.scrollPane = scrollPane;
        this.canvas = canvas;
        this.minScale = minScale;
        this.maxScale = maxScale;
    }

    public ZoomHandler(ScrollPane scrollPane, Pane canvas) {
        this(scrollPane, canvas, 0.1, 10);
    }

    @Override
    public void handle(ScrollEvent e) {
        if (e.isControlDown()) {
            double actualScale = canvas.getScaleX();

            if (actualScale > maxScale || actualScale < minScale) {
                e.consume();
                return;
            }

            double hVal = scrollPane.getHvalue();
            double vVal = scrollPane.getVvalue();

            double scale, factor;           
            if (e.getDeltaY() > 0) {
                factor = 1.1;
            } else {
                factor = 0.9;
            }
            scale = actualScale * factor;

            scale = Math.min(scale, maxScale);
            scale = Math.max(scale, minScale);

            canvas.setScaleX(scale);
            canvas.setScaleY(scale);

            scrollPane.setHvalue(hVal);
            scrollPane.setVvalue(vVal);

            e.consume();
        }
    }

}

Main.java

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ScrollPane;
import javafx.scene.layout.*;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Rectangle;
import javafx.scene.text.Text;
import javafx.stage.Stage;

public class Main extends Application  {     

    public static final int CANVAS_WIDTH = 1000;
    public static final int CANVAS_HEIGHT = 1000;

    private final Pane canvas = new Pane();
    private final ScrollPane scrollPane = new ScrollPane(); 
    private final ZoomHandler zoomHandler = new ZoomHandler(scrollPane, canvas);

    public static void main(String[] args) { launch(args); }
    @Override public void start(Stage primaryStage) {        
        canvas.setPrefWidth(CANVAS_WIDTH);
        canvas.setPrefHeight(CANVAS_HEIGHT);
        canvas.setOnScroll(zoomHandler);        

        scrollPane.setStyle("-fx-background-color: transparent; -fx-control-inner-background: transparent;");
        scrollPane.setContent(new Group(canvas));
        scrollPane.setPannable(true);
        scrollPane.setOnScroll(zoomHandler);

        addContent();

        Scene scene = new Scene(scrollPane, 800, 600);

        primaryStage.setTitle("Zoom");
        primaryStage.setScene(scene);
        primaryStage.show();

        scrollPane.setHvalue(0.5);  
        scrollPane.setVvalue(0.5);  
    }

    private void addContent() {
        Text hello = new Text(400, 500, "Hello");
        hello.setStyle("-fx-font-size: 20px; -fx-fill: red;");

        Text world = new Text(500, 600, "world!");
        world.setStyle("-fx-fill: blue;");

        Text text = new Text(200, 350, "How to zoom to this text when mouse is over?");
        text.setStyle("-fx-font-weight: bold;");

        Rectangle rect = new Rectangle(600, 450, 300, 200);
        rect.setFill(Color.GREEN);

        Circle circle = new Circle(250, 700, 100);
        circle.setFill(Color.YELLOW);

        canvas.getChildren().addAll(hello, world, text, rect, circle);
    }

}

Any ideas? Thanks in advance.

1
2
5/23/2017 11:51:15 AM

I had the same problem and I did the following - I wouldn't call is a proper solution (rather a workaround), but it works mostly fine.

Basically, I do some calculations to retrieve the correct values of Hvalue and Vvalue. Moreover, I have to apply a compensation factor due to the fact that the ScrollPane will do not only the zooming but also a vertical translation of the image (due to standard behaviour of the ScrollPane).

Here you find the code.

/**
 * Pane containing an image that can be resized.
 */
public class SizeableImageView extends ScrollPane {
    /**
     * The zoom factor to be applied for each zoom event.
     *
     * (480th root of 2 means that 12 wheel turns of 40 will result in size factor 2.)
     */
    private static final double ZOOM_FACTOR = 1.0014450997779993488675056142818;

    /**
     * The zoom factor.
     */
    private final DoubleProperty zoomProperty = new SimpleDoubleProperty(1000);

    /**
     * The mouse X position.
     */
    private final DoubleProperty mouseXProperty = new SimpleDoubleProperty();

    /**
     * The mouse Y position.
     */
    private final DoubleProperty mouseYProperty = new SimpleDoubleProperty();

    /**
     * Constructor without initialization of image.
     */
    public SizeableImageView() {
        this(new ImageView());
    }

    /**
     * Constructor, initializing with an image view.
     *
     * @param imageView
     *            The ImageView to be displayed.
     */
    public SizeableImageView(final ImageView imageView) {
        setContent(imageView);

        setPannable(true);
        setHbarPolicy(ScrollBarPolicy.NEVER);
        setVbarPolicy(ScrollBarPolicy.NEVER);

        setOnMouseMoved(new EventHandler<MouseEvent>() {
            @Override
            public void handle(final MouseEvent event) {
                mouseXProperty.set(event.getX());
                mouseYProperty.set(event.getY());
            }
        });

        addEventFilter(ScrollEvent.ANY, new EventHandler<ScrollEvent>() {
            @Override
            public void handle(final ScrollEvent event) {
                ImageView image = (ImageView) getContent();

                // Original size of the image.
                double sourceWidth = zoomProperty.get() * image.getImage().getWidth();
                double sourceHeight = zoomProperty.get() * image.getImage().getHeight();

                zoomProperty.set(zoomProperty.get() * Math.pow(ZOOM_FACTOR, event.getDeltaY()));

                // Old values of the scrollbars.
                double oldHvalue = getHvalue();
                double oldVvalue = getVvalue();

                // Image pixels outside the visible area which need to be scrolled.
                double preScrollXFactor = Math.max(0, sourceWidth - getWidth());
                double preScrollYFactor = Math.max(0, sourceHeight - getHeight());

                // Relative position of the mouse in the image.
                double mouseXPosition = (mouseXProperty.get() + preScrollXFactor * oldHvalue) / sourceWidth;
                double mouseYPosition = (mouseYProperty.get() + preScrollYFactor * oldVvalue) / sourceHeight;

                // Target size of the image.
                double targetWidth = zoomProperty.get() * image.getImage().getWidth();
                double targetHeight = zoomProperty.get() * image.getImage().getHeight();

                // Image pixels outside the visible area which need to be scrolled.
                double postScrollXFactor = Math.max(0, targetWidth - getWidth());
                double postScrollYFactor = Math.max(0, targetHeight - getHeight());

                // Correction applied to compensate the vertical scrolling done by ScrollPane
                double verticalCorrection = (postScrollYFactor / sourceHeight) * event.getDeltaY();

                // New scrollbar positions keeping the mouse position.
                double newHvalue = ((mouseXPosition * targetWidth) - mouseXProperty.get()) / postScrollXFactor;
                double newVvalue =
                        ((mouseYPosition * targetHeight) - mouseYProperty.get() + verticalCorrection)
                                / postScrollYFactor;

                image.setFitWidth(targetWidth);
                image.setFitHeight(targetHeight);

                setHvalue(newHvalue);
                setVvalue(newVvalue);
            }
        });

        addEventFilter(ZoomEvent.ANY, new EventHandler<ZoomEvent>() {
            @Override
            public void handle(final ZoomEvent event) {
                zoomProperty.set(zoomProperty.get() * event.getZoomFactor());

                ImageView image = (ImageView) getContent();
                image.setFitWidth(zoomProperty.get() * image.getImage().getWidth());
                image.setFitHeight(zoomProperty.get() * image.getImage().getHeight());
            }
        });

    }

    /**
     * Set the image view displayed by this class.
     *
     * @param imageView
     *            The ImageView.
     */
    public final void setImageView(final ImageView imageView) {
        setContent(imageView);
        zoomProperty.set(Math.min(imageView.getFitWidth() / imageView.getImage().getWidth(), imageView.getFitHeight()
                / imageView.getImage().getHeight()));
    }
}
1
1/4/2015 9:27:47 AM

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