javajavafx：基于2次鼠标点击在画布上绘制一个矩形

Question

我正在尝试创建一个程序，它应该基于两次鼠标左键单击在画布上绘制一个矩形，并通过一次鼠标右键单击清除画布

创建矩形时，第一次鼠标单击模拟矩形的一个角，下一次鼠标单击与第一次鼠标单击相比模拟矩形的对角

我被困在如何存储第一次鼠标单击的坐标上，然后再好好利用第二次鼠标单击，因为每个定义的矩形仅基于一组坐标创建，即矩形的左上角

现在，我的代码所做的就是绘制固定大小的矩形（50x25），这显然不是我想要的。这只是为了看看清理部分是否有效

到目前为止，我得到的是：

package application;

import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.input.MouseButton;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;

public class DrawRectangle extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) {
        primaryStage.setTitle("Title");
        Canvas canv = new Canvas(500, 400);
        GraphicsContext gc = canv.getGraphicsContext2D();

        EventHandler<MouseEvent> event = new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                if (event.getButton() == MouseButton.PRIMARY) {
                    double x = event.getX();
                    double y = event.getY();                    
                    gc.setFill(Color.BLUE);
                    gc.fillRect(x, y, 50, 25);
                }
            }
        };

        canv.addEventHandler(MouseEvent.MOUSE_CLICKED, event);

        EventHandler<MouseEvent> event2 = new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event2) {
                if (event2.getButton() == MouseButton.SECONDARY) {
                gc.clearRect(0, 0, 500, 400);
                }
            }
        };

        canv.addEventHandler(MouseEvent.MOUSE_CLICKED, event2);

        StackPane root = new StackPane();
        root.getChildren().add(canv);

        primaryStage.setScene(new Scene(root, 500, 400));
        primaryStage.show();
    }
}

我不知道鼠标点击矩形的哪个角是否重要，也许有人有什么想法

致以最良好的祝愿，新年快乐

Answer 1

只需将第一个单击点保存在成员变量中，然后使用它，并在用户创建第二个单击点时重置它

注意：下面的示例代码使用来自Java13+的switch expression。如果Java版本中没有开关表达式，请将其转换为标准开关语句或If/else子句

import javafx.application.Application;
import javafx.geometry.*;
import javafx.scene.Scene;
import javafx.scene.canvas.*;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

public class DrawRectangle extends Application {

    private static final int W = 500;
    private static final int H = 400;

    private Point2D savedPoint = null;

    @Override
    public void start(Stage stage) {
        Canvas canvas = new Canvas(W, H);
        GraphicsContext gc = canvas.getGraphicsContext2D();

        canvas.setOnMouseClicked(event -> {
            switch (event.getButton()) {
                case PRIMARY   -> handlePrimaryClick(gc, event);
                case SECONDARY -> gc.clearRect(0, 0, W, H);
            }
        });

        stage.setResizable(false);
        stage.setScene(new Scene(new StackPane(canvas), W, H));
        stage.show();
    }

    private void handlePrimaryClick(GraphicsContext gc, MouseEvent event) {
        Point2D clickPoint = new Point2D(event.getX(), event.getY());

        if (savedPoint == null) {
            savedPoint = clickPoint;
        } else {
            Rectangle2D rectangle2D = getRect(savedPoint, clickPoint);

            gc.setFill(Color.BLUE);
            gc.fillRect(
                    rectangle2D.getMinX(),
                    rectangle2D.getMinY(),
                    rectangle2D.getWidth(),
                    rectangle2D.getHeight()
            );

            savedPoint = null;
        }
    }

    private Rectangle2D getRect(Point2D p1, Point2D p2) {
        return new Rectangle2D(
                Math.min(p1.getX(), p2.getX()),
                Math.min(p1.getY(), p2.getY()),
                Math.abs(p1.getX() - p2.getX()),
                Math.abs(p1.getY() - p2.getY())
        );
    }

    public static void main(String[] args) {
        launch(args);
    }
}