Simple Reactor

int gridWidth = 20; 
int gridHeight = 20; 
float shapeWidth = 30; 
float shapeHeight = 30; 
float reactorScaler = .06;
int xOffset;
int yOffset;
PVector reactorPosition;

void setup() {
  reactorPosition = new PVector(0, 0);
  size(700, 700);
  // offset used to center the graphics on the screen
  xOffset = floor(width/2-(shapeWidth*gridWidth/2));
  yOffset = floor(height/2-(gridHeight*shapeHeight/2));

  background(255);
  smooth();
};

void draw() {
  background(255);
  fill(0);
  noStroke();
  pushMatrix(); 
  translate(xOffset, yOffset);//translate matrix to center 
  for (int i = 0; i<gridWidth; i++ ) {
    for (int j = 0; j<gridHeight; j++ ) {
      PVector myPos = new PVector(i*shapeWidth, j*shapeHeight);
      float reactorDistance = dist(reactorPosition.x, reactorPosition.y, myPos.x, myPos.y);
      float scaler = reactorDistance*reactorScaler;
      ellipse(myPos.x, myPos.y, 1*scaler, 1*scaler);
    };
  };
  popMatrix();
};

int mouse_X() {
  return (mouseX - xOffset); //correct positions after matrix translations
}

int mouse_Y() {
  return (mouseY - xOffset); //correct positions after matrix translations
}
void mouseMoved() {
  reactorPosition.x = mouse_X();
  reactorPosition.y = mouse_Y();
};