I'm the author. The source code is here: https://github.com/Erkaman/cute-deferred-shading

This is a cute little implementation of normal deferred shading. The focus of this implementation was readability and brevity, so that others can learn from the code. The entire renderer is only about 1400 lines of C++ code. Note that there are probably ways in which the implementation can be made faster, but such optimizations were not performed to keep things brief, and readable.