void ofApp::draw(){
    
// for testing whether the image can display correctly.
// image.draw(0, 0);


    for (int i = 0; i < gridSize; i++) {
       for (int j = 0; j < gridSize; j++) {

           if (grid[i][j]) {
               ofSetColor(255);
           } else {
               ofSetColor(0);
           }
           ofDrawRectangle(i*cellSize , j*cellSize , cellSize, cellSize);
//         ofDrawRectangle(i , j , cellSize, cellSize);
       }
    }
}