为什么我的函数没有做它应该做的事情，改变了 javafx 中球的速度方向？

Question

所以我做了一个小程序，其中我有一个球，它应该在跌落时缓慢加速，并在再次跳起时缓慢减速。同时它应该向左和向右移动，基本上是左右弹跳。

我现在遇到的问题是，当球击中 canvas 底部时，应该使球改变 y 轴速度的方法停止改变代数符号，在第一次成功 jump/bounce 球在底部出现故障。

我尝试打印一些东西，如果它进入函数 moveBubbleUp() 并且它在屏幕底部出现故障并且应该向上移动时打印出来再次，为什么代数符号不会改变？打印速度时，它变得越来越大，即使 moveBubbleUp() 中有 bubbleVelocity-=5。

所以该方法被调用，通过在它进入时打印一个随机字符串来证明，但没有做任何我想要它做的事情，同时也完全按照它的对应 moveBubbleDown() 应该做的。当故障发生时它不会被调用，因为我也尝试在那里打印一些东西。

改变速度的方法如下：

void moveBubbleDown() {
    bubbleSpeedY += 5;
    bubbleVelocityY = bubbleSpeedY;
}

void moveBubbleUp() {
    bubbleSpeedY -= 5;
    bubbleVelocityY = -bubbleSpeedY;
}

这里是调用函数然后根据函数更改 y-Pos 的方法：

    //calculates YPos of bubble


    //changes which method should be called, if the ball has left the border 
    //and sets him on the edge of it
        if (bubble.getTranslateY()>=heightPane-radiusBubble) {
            bubble.setTranslateY(heightPane-radiusBubble);
            moveDown=false;
        } else if (bubble.getTranslateY() <= maxHeight) {
            bubble.setTranslateY(maxHeight);
            moveDown=true;
        }

        if (moveDown) {
            moveBubbleDown();
        } else {
            moveBubbleUp();
        }
        final double deltaYBubble = elapsedSeconds * bubbleVelocityY;
        bubble.setTranslateY(bubble.getTranslateY() + deltaYBubble);

为了不遗漏任何内容，我将 post 其余代码，以便您也可以自己尝试：

   import javafx.animation.AnimationTimer;
   import javafx.application.Application;
   import javafx.scene.Parent;
   import javafx.scene.Scene;
   import javafx.scene.layout.Pane;
   import javafx.scene.paint.Color;
   import javafx.scene.shape.Circle;
   import javafx.stage.Stage;

   public class Main extends Application {

       //Global Variables
       private static final int widthPane = 1000;
       private static final int heightPane = 650;
       long lastUpdateTime = 0;

       //canvas
       private Pane root = new Pane();

       //Enemy
       int bubbleSpeedY = 30;
       int bubbleVelocityY = bubbleSpeedY;
       final int bubbleSpeedX = 200;
       int bubbleVelocityX = 0;
       int radiusBubble = 25;
       boolean moveDown=true;
       boolean moveRight=true;
       int maxHeight = 50;
       private Circle bubble = new Circle(radiusBubble, Color.CADETBLUE);

       private Parent createContent() {
           root.setPrefSize(widthPane, heightPane);

           root.getChildren().addAll(bubble);

           return root;
       }

       @Override
       public void start(Stage stage) throws Exception{

           bubble.setTranslateY(maxHeight);
           bubble.setTranslateX((int)(Math.random()*widthPane));

           Scene scene = new Scene(createContent());

           final AnimationTimer gameAnimation = new AnimationTimer() {
               @Override
               public void handle(long timestamp) {
                   update(timestamp);
               }
           };
           gameAnimation.start();

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


       /**
        * changes velocity so that the bubble goes to the right
        */
       void moveBubbleRight() {
           bubbleVelocityX = bubbleSpeedX;
       }

       /**
        * changes velocity so that the bubble goes to the left
        */
       void moveBubbleLeft() {
           bubbleVelocityX =-bubbleSpeedX;
       }

       void moveBubbleDown() {
           bubbleSpeedY += 5;
           bubbleVelocityY = bubbleSpeedY;
       }

       void moveBubbleUp() {
           bubbleSpeedY -= 5;
           bubbleVelocityY = -bubbleSpeedY;
       }


       /**
        * updates the pos of the bubble depending on the velocity,
        * looks if it's about to leave the border,
        * and sets it on the edge if it is
        *
        * @param timestamp helps calculate the time that has passed since the last update / frame
        */
       private void update(long timestamp) {
           if (lastUpdateTime > 0) {

        
               final double elapsedSeconds = (timestamp - lastUpdateTime) / 1_000_000_000.0 ;


               //bubble
               //calculates YPos of bubble


               //changes which method should be called, if the ball has left the border 
               //and sets him on the edge of it
               if (bubble.getTranslateY()>=heightPane-radiusBubble) {
                   bubble.setTranslateY(heightPane-radiusBubble);
                   moveDown=false;
               } else if (bubble.getTranslateY() <= maxHeight) {
                   bubble.setTranslateY(maxHeight);
                   moveDown=true;
               }

               if (moveDown) {
                   moveBubbleDown();
               } else {
                   moveBubbleUp();
               }
               final double deltaYBubble = elapsedSeconds * bubbleVelocityY;
               bubble.setTranslateY(bubble.getTranslateY() + deltaYBubble);


               //calculates XPos of Bubble
               if (bubble.getTranslateX() >= widthPane - radiusBubble) {
                   bubble.setTranslateX(widthPane - radiusBubble);
                   moveRight=false;
               } else if (bubble.getTranslateX() - radiusBubble <= 0) {
                   moveRight=true;
               }

               if (moveRight) {
                   moveBubbleRight();
               } else {
                   moveBubbleLeft();
               }

               final double deltaXBubble = elapsedSeconds * bubbleVelocityX;

               bubble.setTranslateX(bubble.getTranslateX() + deltaXBubble);

           }
           lastUpdateTime=timestamp;
       }

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

感谢大家的帮助，因为我对编码还不是很熟悉，而且我认为这个问题远远超出了我的代码知识范围。好吧，也许这是我忽略的一个愚蠢的小错误，这会毁了一切。

Answer 1

这与你撞到“地板”时的速度有关。简单的时间更改可以使它不会发生。我认为速度是这样的，气泡不能正确地离开地板，所以它被卡住了，触发了撞到地板的情况。我在 moveUp/Down 调用后立即添加了垂直气泡速度的打印，然后它不再卡住了！

我对您的代码做了一些小改动以简化垂直移动，现在情况似乎更好了：

package Whosebug.answers.demo;

import javafx.animation.AnimationTimer;
import javafx.application.Application;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;

public class Main extends Application {

    //Global Variables
    private static final int widthPane = 1000;
    private static final int heightPane = 650;
    long lastUpdateTime = 0;

    //canvas
    private Pane root = new Pane();

    //Enemy
    double bubbleAccelerationY = 300;
    double bubbleSpeedY = 30;
    double bubbleVelocityY = bubbleSpeedY;
    final int bubbleSpeedX = 200;
    int bubbleVelocityX = 0;
    int radiusBubble = 25;
    boolean moveDown = true;
    boolean moveRight = true;
    int maxHeight = 50;
    private Circle bubble = new Circle(radiusBubble, Color.CADETBLUE);

    private Parent createContent() {
        root.setPrefSize(widthPane, heightPane);
        root.getChildren().addAll(bubble);
        return root;
    }

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

    @Override
    public void start(Stage stage) throws Exception {

        bubble.setTranslateY(maxHeight);
        bubble.setTranslateX((int) (Math.random() * widthPane));

        Scene scene = new Scene(createContent());

        final AnimationTimer gameAnimation = new AnimationTimer() {
            @Override
            public void handle(long timestamp) {
                update(timestamp);
            }
        };
        gameAnimation.start();

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

    /**
     * changes velocity so that the bubble goes to the right
     */
    void moveBubbleRight() {
        bubbleVelocityX = bubbleSpeedX;
    }

    /**
     * changes velocity so that the bubble goes to the left
     */
    void moveBubbleLeft() {
        bubbleVelocityX = -bubbleSpeedX;
    }

    void accelerateBubble(double secs) {
        bubbleVelocityY += (secs * bubbleAccelerationY);
    }

    void bounceBubble() {
        bubbleVelocityY = -bubbleVelocityY;
    }

    /**
     * updates the pos of the bubble depending on the velocity, looks if it's about to leave the border, and sets it on
     * the edge if it is
     *
     * @param timestamp helps calculate the time that has passed since the last update / frame
     */
    private void update(long timestamp) {
        if (lastUpdateTime > 0) {

            final double elapsedSeconds = (timestamp - lastUpdateTime) / 1_000_000_000.0;

            //bubble
            //calculates YPos of bubble
            //changes which method should be called, if the ball has left the border
            //and sets him on the edge of it
            if (bubble.getTranslateY() >= heightPane - radiusBubble) {
                bubble.setTranslateY(heightPane - radiusBubble);
                bounceBubble();
            } else if (bubble.getTranslateY() <= maxHeight) {
                bubble.setTranslateY(maxHeight);
            }

            accelerateBubble(elapsedSeconds);

            final double deltaYBubble = elapsedSeconds * bubbleVelocityY;
            bubble.setTranslateY(bubble.getTranslateY() + deltaYBubble);

            //calculates XPos of Bubble
            if (bubble.getTranslateX() >= widthPane - radiusBubble) {
                bubble.setTranslateX(widthPane - radiusBubble);
                moveRight = false;
            } else if (bubble.getTranslateX() - radiusBubble <= 0) {
                moveRight = true;
            }

            if (moveRight) {
                moveBubbleRight();
            } else {
                moveBubbleLeft();
            }

            final double deltaXBubble = elapsedSeconds * bubbleVelocityX;

            bubble.setTranslateX(bubble.getTranslateX() + deltaXBubble);

        }
        lastUpdateTime = timestamp;
    }
}

为什么我的函数没有做它应该做的事情，改变了 javafx 中球的速度方向？

Why is my function not doing what its supposed to, changing the direction of the velocity of a ball in javafx?

java

geometry

javafx