int cols;
int rows;

float[][] current;
float[][] previous;

float damping = 0.99;

void setup()
{
  size(600, 400);
  cols = width;
  rows = height;
  current = new float[cols][rows];
  previous = new float[cols][rows];
}

void mouseMoved()
{
  previous[mouseX][mouseY] = 2055;
}

void keyPressed()
{
  save("output.png");
}

void draw()
{

  background(0);

  int x = (int)random(0,(int)width);
  int y = (int)random(0,(int)height);
  previous[x][y] = random(2000);
  
  loadPixels();
  for ( int  i = 1; i < cols-1; i++ ) {
    for ( int j = 1; j < rows-1; j++ ) {
      current[i][j] = (
        previous[i-1][j]+
        previous[i+1][j]+
        previous[i][j-1]+
        previous[i][j+1])/2.0 - current[i][j];
        
      current[i][j] = current[i][j]*damping;
      int index = i + j * cols;
      pixels[index] = color(100-current[i][j]);
    }
  }

  updatePixels();

  float[][] temp = previous;
  previous = current;
  current = temp;
 
}