java如何限制圆在直线上的拖动。JavaFX

Question

假设我在窗格上有一个线条，我想要圆形。如何限制圆的拖动，使圆只能在直线上左右拖动，而不能在其他任何地方拖动

Answer 1

此实现遵循线路，不经过线路末端

The key to following is y = mx + b. m = slope of line and b = y-intercept.

Here is a crude implementation:

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.AnchorPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Line;
import javafx.stage.Stage;

/**
 *
 * @author blj0011
 */
public class JavaFXApplication42 extends Application {
    
    @Override
    public void start(Stage primaryStage) {
        AnchorPane root = new AnchorPane();
        
        Line line = new Line(20, 120, 70, 170);
        line.setStrokeWidth(3);
        
        //When the line is clicked by the mouse add a circle
        line.setOnMouseClicked((mouseClickedEvent )->{
            Circle c1 = new Circle(mouseClickedEvent.getSceneX(), mouseClickedEvent.getSceneY(), 25, Color.BLUE);
            //When the circle is dragged follow the line
            c1.setOnMouseDragged(mouseDraggedEvent -> {
                double slope = lineSlope(line.getStartX(), line.getEndX(), line.getStartY(), line.getEndY());
                double yIntercept = yIntercept(slope, line.getStartX(), line.getStartY());
                c1.setCenterY(setCenterY(slope, mouseDraggedEvent.getSceneX(), yIntercept));
                c1.setCenterX(mouseDraggedEvent.getSceneX());
                
                //Bound checks to make sure circle does not go pass the line ends
                if(c1.getCenterX() > line.getEndX())
                {
                    c1.setCenterX(line.getEndX());
                }
                else if(c1.getCenterX() < line.getStartX())
                {
                    c1.setCenterX(line.getStartX());
                }
                
                if(c1.getCenterY() > line.getEndY())
                {
                    c1.setCenterY(line.getEndY());
                }
                else if(c1.getCenterY() < line.getStartY())
                {
                    c1.setCenterY(line.getStartY());
                }
            });
            root.getChildren().add(c1);
        });
        
        
        
        root.getChildren().add(line);
        
        Scene scene = new Scene(root, 300, 250);
        
        primaryStage.setTitle("Hello World!");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        launch(args);
    }
    
    double lineSlope(double x1, double x2, double y1, double y2)
    {
        if(x2 - x1 == 0)
        {
            return 0;
        }
        
        return (y2 - y1)/(x2 - x1);
    }
    
    double yIntercept(double slope, double x1, double y1)
    {
        return y1 - (slope * x1);
    }
    
    double setCenterY(double slope, double x, double  yIntercept)
    {
        return slope * x + yIntercept;
    }    
}