// x and y positions
int[] xpos = new int[50];
int[] ypos = new int[50];

void setup() {
  size(200,200);
  smooth();
  // Initialize
  for (int i = 0; i < +xpos.length; i++) {
    xpos[i] = 0;
    ypos[i] = 0;
  }  
}

void draw() {
  background(255);
  // Shift array values
  for (int i = 0; i < xpos.length-1; i++ ) {
    xpos[i] = xpos[i + 1];
    ypos[i] = ypos[i + 1];
  }
  // New location
  xpos[xpos.length-1] = mouseX;
  ypos[ypos.length-1] = mouseY;
  // Draw everything
  for (int i = 0; i < xpos.length; i++ ) {
    noStroke();
    fill(255-i*5);
    ellipse(xpos[i],ypos[i],i,i);
  }
}