Let’s Talk About Touch (Part1):
Windows Mobile (and CE) has supported touch screen interfaces since the beginning but the release of Windows Mobile 6.5 brings something new to the platform: gesture support. Gestures are intended to be a more natural way of interacting with the device through the touch screen, making more of an emotional connection between the user and the applications under the finger or stylus. Technically gestures are a collection of input points generated by touching the screen in patterns that the system recognizes. However the touch solution is much more than just the gestures, it’s also about the animation and interaction that take place as a result of the gesture input, for example smoothly scrolling a list of items or ensuring a UI item remains fixed to the ‘finger’ to give the illusion that the user is directly manipulating the screen content as if it were tangible.
What’s the difference between gestures and simple mouse input?
At first glance there appears to be a lot of commonality between raw mouse messages and gesture messages such as select = mouse click, pan = mouse move and double select = double click. However the gesture recognition code is designed to handle a quite difference set of input limitations to the mouse input. Primarily the mouse input for mobile devices is expected to originate with a pointing device like a stylus or a physical mouse; however gesture messages are expected to originate from a variety of sources such as using a finger or thumb, or by shaking the device and even broader input like smile recognition from a camera. Most users will initially experience gestures through the touch screen input and the majority of the work in 6.5 has been around getting finger input and response right.
Using a stylus or a mouse results in surprisingly accurate touch data which in turn makes small screen controls a viable user experience. In this situation tolerances for click, double click and tap’n’hold can be very small.
However when using a finger instead of a stylus several things have to change – for example the tolerances for click , double click, and tap’n’hold need to grow significantly to handle the huge variety of finger shapes and sizes found out in the wilds of human kind. Additionally when moving your finger across the screen the shape pressed against the screen changes due to the angle the finger is at. This often leads to unexpected input points at the end of a pan input that can cause misinterpretation of the movement
A Word about Screens
Touch enabled Windows Mobile devices traditionally sport a plastic tipped stylus and have a touch screen based on resistive technology.
In brief resistive screen technology is based on two layers of transparent conducting material (Indium Tin Oxide or ITO) separated by an air gap held apart with tiny insulating plastic beads. Pressing the screen deforms the two sheets and makes contact between them and from the change in resistance the screen firmware can identify where the stylus has been placed. There are lots of variations on this technology.
Resistive screens have several killer properties: they are cheap, very accurate for a stylus, and they can continue to work in quite hostile environments i.e. dirty screens.
However they do suffer in other areas: they require an amount of force to deform the screen and make contact between the conducting layers; because of the multi plastic layers placed on top of the display and the air gap, some brightness is always lost; cheap & readily available traditional resistive screens really only support a single touch point - more advanced digital resistive sensors have been demonstrated which do support multiple touch points, but this is a future development; it’s quite tough to get more information beyond just the point location i.e. size of the touch area; and durability can be an issue due to the use of moving parts – i.e. deformation of the screen.
Another touch technology that has rapidly gained in popularity is capacitive (as found in the iPhone and Android G1). This technology works by continually measuring the capacitive property of different areas of the screen. When conducting material such as a finger is placed on the screen, its capacitive properties change and the screen driver can determine where the finger is based upon the changes.
Capacitive technology has several advantages: zero pressure is required to make an input because nothing needs to be deformed and this leads to a much more natural interface experience; although additional material is laid onto the screen, there is no air gap so optical clarity is much improved reducing the need for backlighting making power draw lower; multiple touch points can be supported; things like touch size and pressure can be extrapolated from the capacitive data.
However they do suffer in other areas: in general the cost is currently higher than the equivalent resistive screen; supporting a stylus is hard because it must be made of conducting material and must make sufficient contact to change the capacitive property of the screen; in several areas the accuracy tends to be lower than resistive e.g. around the edges of the screen, combined with the lack of a stylus and lower sample rates makes things like handwriting input very hard.
There are other input technologies developing all the time, but at the moment these two represent nearly all the market for mobile devices.
Windows Mobile 6.5 has primarily been designed for resistive screens because some input areas still rely on small controls and require a high level of input accuracy that can’t be easily achieved with a finger and require a stylus; however some device manufacturers are considering options to ship capacitive screens.
Looking forward the mobile team is considering how to address these issues and support many more screen types including capacitive.
What Gestures are supported?
In Windows Mobile 6.5 we have implemented five primary gestures:
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