如何使矩形角的圆反弹 - 处理

Question

I will keep this quick.

Just making a processing program where the ball bounces off the rectangle.

At the moment I can only figure out how to do the top,left,right and bottom sides but when the ball goes into the corners of the rectangle, it doesn't bounce off but instead goes into the rectangle and after 1 or 2 bounces gets realeased.

I just really want to know how I should go about making the ball deflect off the corners of the rectangle so it doens't glitch

Here is my code :

    float x = 100, y = 100, radius = 50;
    float vx = 3, vy = 3;
    float MX = 0;
    float MY = 0;


    void setup() {
        size(500, 700);
    }

    void draw() {
        background(0);
        fill(255);

        x += vx;
        y += vy;
        if (x + radius > width) {
            vx = vx * -1;
        }
        //makes the ball bounce off the right
        if (x - radius < 0) {
            vx = vx * -1;
        }
        //makes the ball bounce off the left
        if (y + radius > height) {
            vy = vy * -1;
            y = height - radius;
        }
        //make the ball bounce off the top
        if (y - radius < 0) {
            vy = vy * -1;
            y = radius;
        }
        //makes the ball bounce    off the top
        if (y + radius > MY && x + radius > MX + 50 && x + radius < MX + 150 &&
            y + radius < MY + 20) {
            vy *= -1;
            y = MY - 3 - radius;
        } //Top Side
        if (x - radius < MX + 100 && y > MY - 10 && y < MY + 10 && x - radius > MX) {
            vx *= -1;
        } // Right Side

        if (y - radius < MY + 20 && x + radius > MX + 50 && x + radius < MX + 150 &&
            y - radius > MY) {
            vy *= -1;
            y = MY + 20 + radius;
        } //Bottom Side

        if (x + radius > MX && y > MY - 10 && y < MY + 10 && x + radius < MX + 100) {
            vx *= -1;
        } // Left Side

        ellipse(x, y, radius * 2, radius * 2);
        rect(MX, MY, 100, 20);

    }

void mouseMoved() {

        MX = mouseX - 50;
        MY = mouseY - 10;
        if (MX < 0) {
            MX = 0;
        }
        if (MX > 400) {
            MX = 400;
        }
        if (MY < 0) {
            MY = 0;
        }
        if (MY > 680) {
            MY = 680;
    }

Sorry I do know know how to insert the code very well, I am new to this site, please have mercy haha :)

Cheers

Answer 1

The problem is not that you need to detect corner collision. You've got two other problems:

Problem 1: When you detect a collision, you need to move the ball so it's not colliding with the rectangle anymore.

If you don't, then when the ball intersects the top of the box, you multiply the vy variable by -1 . That causes the circle to start moving up. But the next frame, the circle is still colliding with the rectangle, because it hasn't moved up enough yet. So your code detects that collision, multiples vy by -1 again, and the ball moves back down. Next frame the same thing happens, until the ball eventually stop colliding with the rectangle.

Slow the framerate down to see what I'm talking about:

To fix this, you need to "pop" the ball back to a location that's no longer intersecting with the rectangle. That way you know it won't still be colliding in the next frame.

Problem 2: You shouldn't do collision on each side separately. Instead, do collisions between the entire circle and the entire rectangle, and then check one axis of movement at a time.

Checking against one side at a time will lead to plenty of headaches, including the problem where multiple sides are hit at one time. I would also bet that your code isn't doing what you think it is: try adding println() statements to all of your if statements to make sure they're executing when you think they are.

To fix this problem, I would create a collides() function that takes parameters for the next position of the ball, and returns whether the ball will be colliding with any side of the rectangle. Then pass in the next X and Y positions and flip their speeds. It'll look something like this:

 if (collides(circleX + vx, circleY)) {
    vx*=-1;
  } 
  else {
    circleX += vx;
  }
  if (collides(circleX, circleY + vy)) {
    vy*=-1;
  } 
  else {
    circleY += vy;
  }

You'd also want to add the logic for "popping" the ball so it's no longer colliding.

PS: Did you try searching for your problem on google or the Stack Overflow search? This question is almost an exact duplicate of your question, to the point where I'm pretty sure you're in the same class!

Answer 2

A quick dirty way i have previously achieved this is by first adding bounding boxes to each side and positioning them in a way that if the ball collides with for example on the top right corner i would then have a condition:

If ball intercepts bounds top and bounds right: do this;

I hope this helps!