Orbiting issues

Processing Coding Questions
1

I am trying to make a circle orbit the larger circle in this cord. My attempts have been failing. Please help


ArrayList Balls;
int mass;
byte h;
PFont font;
int x = mass;

void setup(){
  size(640, 640);
  frameRate(60);

  Balls = new ArrayList();
  mass = 400;
  h = 80;
  font = createFont("Onyx", 12);
}

float distance(PVector pos, PVector pos2){
  return sqrt(((pos.x-pos2.x)*(pos.x-pos2.x))+((pos.y-pos2.y)*(pos.y-pos2.y)));
}

PVector grav(PVector pos){
  PVector direction = new PVector(width/2 - pos.x, height/2 - pos.y);
  direction.normalize();
  float d = distance(pos, new PVector(width/2+1, height/2+1));
  direction.mult(mass/(d*d));
  return direction;
}
  

class Ball{
  PVector position;
  PVector velocity;
  Ball(float px, float py, float vx, float vy){
    position = new PVector(px, py);
    velocity = new PVector(vx/50, vy/50);
  }
  void drawball(){
    PVector gravity = grav(position);
    PVector velgrav = velocity;
    velgrav.add(gravity);
    position.add(velgrav);
    ellipse(position.x, position.y, 10, 10);
  }
}

void draw(){
  background(0);
  text("w - initial height up", 10, 10);
  text("s - initial hieght down", 10, 20);
  text("c - clear", 10, 30);
  float ds = distance(new PVector(mouseX, mouseY), new PVector(width/2, height/2 - 60));
  stroke(200*(ds/250), 100, 50);
  strokeWeight(4);
  line(width/2, height/2 - h, mouseX, mouseY);
  fill(150);
  noStroke();
  ellipse(width/2, height/2,100,100);
  for (int i = Balls.size()-1; i >= 0; i--){
    Ball a = (Ball) Balls.get(i);
    a.drawball();
    float dis = distance(a.position, new PVector(width/2, height/2));
    if ( dis < 60 || dis > 2000){
      Balls.remove(i);
    }
    if ( dis < 80){
      mass = x/20;
      x = -abs(x);
      println(x);
      }else{
      x = x+25;
      x=-x*40;
      println(x);
      if(x>5000){
        x=25;
      }
    }
  }
}


void mousePressed(){
  Balls.add(new Ball(width/2, height/2 - h, mouseX - width/2, mouseY - (height/2 - h)));
}

void keyPressed(){
  if (key == 'w' && h < 121){
    h++;
  }else if (key == 's' && h > 61){
    h--;
  }else if (key == 'c'){
    for (int i = Balls.size()-1; i >= 0; i--){
      Balls.remove(i);
      mass = 400;
    }
  }
}
1 Like
2

It may be because the velocity is too small to to move the ball off it’s initial path

I found that getting rid of the velGrav intermediate and directly applying the gravity to velocity produced better results.

Also, the calculation causes the balls to move away from the center, not towards.

3

Code please. I don’t know how to make that change

4

Like I said, In void drawball() in the Ball class, make this change

velocity.sub(gravity);
position.add(velocity);

Edit: I also noticed that the same balls launched from the same place have varying velocities, which I feel shouldn’t be the case?

Commenting out line that says “mass = x/20” produces better results

1 Like