private static String loadShader(String fileName){
        StringBuilder shaderSource = new StringBuilder();

        BufferedReader shaderReader;

        try{
            shaderReader = new BufferedReader(new FileReader("./res/shader/" + fileName));
            String line;

            while ((line = shaderReader.readLine()) != null){
                shaderSource.append(line).append("\n");
            }

            shaderReader.close();
        }catch (Exception e){
            e.printStackTrace();
            System.exit(1);
        }


        return shaderSource.toString();
    }