This is an example game 'Flappy Gopher' that was written for my keynote at GoCon Tokyo Winter 2015.
This game is now an official example in the x/mobile repository. Its canonical location is golang.org/x/mobile/example/flappy (use 'go get').
The git history shows the step-by-step development of the game. When I gave the keynote, I demonstrated this using the dt tool. See https://github.com/adg/dt/.
The sprites were created by Renee French and are distributed under the Creative Commons Attributions 3.0 license.