Why doesn't Snake have an on-screen d-pad controller?
We experimented extensively with an on-screen d-pad for controlling Snake, but we found it was much more difficult to use than we initially anticipated. Specifically we noticed that during gameplay our thumbs had a tendency to drift away from the on screen buttons due to the lack of tactile feedback - a glass screen has no physical landmarks for your thumb to feel and align with. This caused us to constantly glance at our fingers or thumbs to see why the snake didn't turn in the direction we had anticipated only to realize our fingers weren't in the right spot anymore. That brief interruption was enough to cause an excessive number of crashes and near-misses while playing the game which was very frustrating.
The control scheme we ultimately settled on supports both swiping and a tap-and-hold method that we found to be much better than a virtual d-pad. Click here for a detailed description of Snake's controls.