当两个矩形在 Java 中触摸时，如何使它们相互检测？

Question

  if(rect3.a+30>rect2.a){


        ballright=false;
        bounce++;
    }
     if(rect3.a-30<rect1.a){

        ballright=true;
        bounce++;
    }

 public void paint(Graphics g){
    super.paint(g);
    Graphics2D g2d=(Graphics2D) g;
    g.setColor(Color.BLACK);
    g.fillRect(0, 0, 1080, 760);

    g2d.setColor(Color.WHITE);
   // g.fillOval(x, y, 30, 30);
   g2d.fillRect(rect3.a, rect3.b, 30, 30);


    g2d.setColor(Color.WHITE);
    g2d.fillRect(rect1.a, rect1.b, 30, 200);

    g2d.setColor(Color.WHITE);
    g2d.fillRect(rect2.a, rect3.b-50, 30, 200);

    g2d.fillRect(520, 0, 10, 760);

So I have these rectnagles to be the objects for a pong game. Except I cant seem to figure out how to make the ball (rect3) bounce of the paddles (rect1,2) and if the paddles is not there go to the edge of the window to score a point. The way I have it now it simply bounces of the whole y axis at 0 and 1080. Is there a way to make it bounce only when the paddle is there and if it is not score a point?

Answer 1

Let's start with the basic objects here:

1. Left Paddle (left:top:height:width = x1, y1, h, w)
2. Right Paddle (left:top:height:width = x2, y2, h, w)
3. Ball (centreXpos:centreYpos:radius = bx, by, r)
4. Board (left:top:height:width = boardX, boardY, boardH, boardW)

Note: - width here refers to the short side - height refers to the length of the long side of rectangle

Now that we have the objects out the way let's identify edges against which you want to detect collision:

1. Left Paddle - Collision surface would be the long right side (ie All pixels from x=(left + width) y=top to x=(left + width) y = (top + height))

2. Right Paddle - Collision surface would be the long left side (ie All pixels from x=(left) y=top to x=(left) y = (top + height))

3. Ball - Collision surface is all pixels on the edge of the circle - so bx +/- radius and by +/- radius

4. Board - Collision surface are the edges of the board - Long edges should cause you to bounce - short edges should end the rally

Collision detection - if collision surface of the ball is >= collision surface of right side paddle or - if collision surface of the ball is <= collision surface of left side paddle

What to do when collision is detected? - if collision is detected with left paddle change direction to move to right (change increments to bx and by to make it take a different direction) - if collision is detected with left end but not the paddle stop animation - if collision is detected with right paddle change direction to move to left - if collision is detected with right end but not the paddle stop animation

Suggestion around Objects

It would help if you modelled your objects and then in your animation loop called collision detector with each surface that you care about The collision detector could then respond with an enumeration. You can have another function act based on the enumeration

From what I see so far you would need

GameObjects
|-- Ball
|-- Paddle
    |-- Left
    |-- Right
|-- Board

you can choose to use inheritance.

CollisionDetector

• iterate through all Game objects and Detect if ball has collided with any surfaces that interest you
• Here you could get both object say, Ball and Left-Paddle and have specific collision routines written for each

( BTW.... with this you can even write test cases around Collision detection and ball movement rather than trying to play it everytime to see if it works as expected )

I believe this will make it simpler. If you have a running copy somewhere on github I am happy to help you with it.

Reading back on the above seems like a long-winded explanation for what you were looking for and something more.

The above does not really depend on Java.. you could do that in almost any language.

Hope this helps:)

Answer 2

you are only checking if ball.x + ball.width > paddle.x you should also account for the case that ball.y is between paddle.y and paddle.y + paddle.height