I have a full-screen game in HTML+JavaScript, which uses the arrow keys as primary controls. This cannot be used on keyboardless Android devices (I haven't tested on iOS), and even if the soft keyboard had arrow keys it would take up unnecessary space. Therefore, I have added onscreen control buttons. However, the buttons are unnecessary (and absurdly large) on desktop browsers, so I would like them to not pop up unless they are needed. What heuristics can I use to decide whether they are needed — that is, whether it is impossible or awkward for the user to input arrow-key events — other than recognizing specific User-Agents (which is straightforward, but not future-proof)? I will of course allow the user to hide/show the buttons; I am looking for useful heuristics for choosing the default setting. Source: Tips4all