simple ik

js + p5

https://editor.p5js.org/kitasenjudesign/sketches/43JWJ7gZw

var balls = [];

function setup() {
  
  createCanvas(window.innerWidth, window.innerHeight);

  for(var i=0;i<10;i++){
    
    var b = new Ball();
    balls.push(b);
    
  }
  
  
}

function draw() {
  
  background(220);

  //console.log(balls[0].x);
  
  balls[0].x = mouseX;
  balls[0].y = mouseY;
  
  for(var i=0;i<balls.length;i++){
    
    if(i>=1){
      
      var ballA=balls[i];
      var ballB=balls[i-1];
      
      var dx = ballA.x - ballB.x;
      var dy = ballA.y - ballB.y;
        
      var rad = Math.atan2(dy,dx);
      
      var size = balls[i].size/2 + balls[i-1].size/2;
      
      balls[i].x = ballB.x + size*Math.cos(rad);
      balls[i].y = ballB.y + size*Math.sin(rad);
      
      /*
       for(var j=0;j<balls.length;j++){
        if(i==j)continue;
        
        var ddx = ballA.x - balls[j].x;
        var ddy = ballA.y - balls[j].y;
        var dd = sqrt(ddx*ddx+ddy*ddy);
        var ss = ballA.size/2+balls[j].size/2;
        
        if(dd<ss){
          ballA.size=2*(dd-balls[j].size/2);           
        }
         
      }*/
      
      
    }
    
    balls[i].draw();
  }
  
}  

class Ball {
 
  constructor() {
    this.x=random()*100;
    this.y=random()*100;
    
    this.size=random()*50+20;
    this.baseSize=this.size;
  }

  update() {
    
  }


  draw() {
 //   stroke(col);
    circle(this.x,this.y,this.size);
  }
  
}