sazap10 sazap10 - 3 months ago 33
Java Question

Zooming in and out using Scroll Event

I am trying to make a group which contains

Rectangle
and
Text
objects to scale up and down using the
ScrollEvent
. I am having trouble getting the correct scale to use from the delta of the scroll. The following code is what I have at the moment. Any help will be appreciated.

Thanks

import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.input.ScrollEvent;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.scene.text.Text;
import javafx.stage.Stage;

// demonstrates scaling a test pane with content in it.
public class ScaleTest extends Application {
Group page;
double textScale =1.0;
public static void main(String[] args) {
launch();
}

@Override
public void start(Stage stage) throws Exception {
stage.setTitle("scale test");
Group root = new Group();
page= new Group();
Rectangle r = new Rectangle(300,300);
Text t = new Text("asodjoijdjiasjdoijaisjdijasijdiajsidjoiasjiodjiajosijdiojaisjdoijaoisjdiojaoisjdjaoisjdiojsoidj\njdoasijdoajsoidjoaisjoidjaoisjdiojs");
t.setFill(Color.FLORALWHITE);
t.setWrappingWidth(280);
t.setX(10);
t.setY(20);
page.getChildren().addAll(r,t);
root.getChildren().add(page);
Scene scene = new Scene(root,800,600);
this.setSceneEvents(scene);
stage.setScene(scene);
stage.show();
}
private void setSceneEvents(final Scene scene) {
//handles mouse scrolling
scene.setOnScroll(
new EventHandler<ScrollEvent>() {
@Override
public void handle(ScrollEvent event) {
double xscale = page.getScaleX() * event.getDeltaY()/35;
double yscale= page.getScaleY() * event.getDeltaY()/35;
System.out.println("xscale: "+ xscale);
System.out.println("yscale: "+ yscale);
//page.setScaleX(page.getScaleX() * event.getDeltaY()/35);
// page.setScaleY(page.getScaleY() * event.getDeltaY()/35);
event.consume();
}
});

}
}

Answer

|deltaY| is for all scroll events the same. Also note that deltaY is negative for scrolling down, and the scaling always is normalized at 1.0. So i suggest to use a "zoom factor" which determines the scaling. Try something like:

private void setSceneEvents(final Scene scene) {
    //handles mouse scrolling
    scene.setOnScroll(
            new EventHandler<ScrollEvent>() {
              @Override
              public void handle(ScrollEvent event) {
                double zoomFactor = 1.05;
                double deltaY = event.getDeltaY();
                if (deltaY < 0){
                  zoomFactor = 2.0 - zoomFactor;
                }
                System.out.println(zoomFactor);
                page.setScaleX(page.getScaleX() * zoomFactor);
                page.setScaleY(page.getScaleY() * zoomFactor);
                event.consume();
              }
            });

  }
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