float gridSize = 100;
float noiseStep = 0.02;

void setup() {
  size(512, 512);
}

void draw() {
  
  float xstep = width/gridSize;
  float ystep = height/gridSize;
  noStroke();
  
  for (int i = 0; i < gridSize; i++) {
    for (int j = 0; j < gridSize; j++) {
      float fillVal = noise(i*noiseStep, j*noiseStep) * 256;
      fill(fillVal);
      rect(xstep * i, ystep * j, xstep, ystep);
    }
  }
  
//  noiseStep = mouseX/(float)width * 0.1;
  
}