Touch input mechanisms have one or more drawbacks. For example, it may be difficult for a user to interact with a display surface of a touch input mechanism without causing inadvertent input events. In one scenario, for example, the user may attempt to perform a task using the computing device that does not involve the touch input mechanism. Yet the user may handle the computing device in a manner which causes inadvertent contact with the display surface. Or the user may accidently brush or bump against the display surface. The touch input mechanism may incorrectly interpret these inadvertent contacts as legitimate input events. In another scenario, the touch input mechanism may accommodate two or more distinct gestures that are nonetheless similar. In this case, the user may intend to enter a particular gesture, but the computing device may mistakenly interpret that gesture as another, similar, gesture. These problems may understandably frustrate the user if they become a frequent occurrence, or, even if uncommon, if they cause significant disruption in the task that the user is performing.
Moreover, a designer may wish to provide an expressive touch input mechanism that accommodates a rich set of input gestures. However, increasing the number of valid gestures may increase the risk of inadvertent input events. This design goal may therefore complicate the above-noted challenges. Further, increasing the number and/or complexity of gestures may make it more difficult for users to understand and memorize the gestures.