Testing Windows 8 on a virtual desktop is a great way to explore the OS, but Windows 8 relies heavily on its touch interface, so how do you mimic the touch experience on a desktop?
You can debate the merits or drawbacks of the Windows 8 touch function all you want, but you can't deny that touch has become a major hardware component as of 2012. Whether it's suited for larger devices -- bigger than what can be comfortably stuck in a pocket -- is still up for debate.
Using a virtual desktop, you can try out Windows 8 without sacrificing a whole machine to do it. Only one problem: In many cases, there is no way to emulate the behavior of touch devices within a virtual machine (VM), even though support for the touch interface is a major reason for Windows 8's existence.
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This isn't a trivial problem. With previous versions of Windows, the mouse and keyboard were the standard input devices for Windows. Now, touch has been added to the mix -- probably for keeps.
Touch devices may support five- or ten-fingered multi-touch, which is all but impossible to emulate with a mouse. It may be possible to emulate that with a touchpad, but that's only if the touchpad supports multi-touch functionality in the first place. It's not something that can be programmed in but requires hardware-level support. (You can use the Windows 8 Simulator and Visual Studio 2012 to emulate touch, but only for the sake of debugging Metro apps, not as a general replacement.)
To help you test Windows 8 in a virtual desktop environment, here are three options for emulating touch devices within a VM that's running Windows 8:
Run your emulation on a device that supports touch, if possible. If you can install your VM software on a system that has touch devices, it may be possible to configure device pass-through so that the touch display is visible to the guest OS.
Note that this would mean anytime you're emulating touch in the VM, you wouldn't be able to use touch in the host OS (assuming you're using it in the first place), because the guest OS would have to commandeer the use of that device. Also, the device would need to run some variety of VM software to do this, and not all such devices are that robust.
Add a touch device to the host. If you don't have a touch-driven system, you may be able to connect a USB touchpad to the host system and use device pass-through to make the device visible to the guest.
The downside to this approach is that you have to buy additional hardware, which may not come cheap. Logitech's T650 can run as much as $80, but it supports multi-finger touch and has native Windows 8 driver support. On the plus side, if you have an existing touch device that can be connected to the system, you can always use that.
You might not have to emulate Windows 8 touch. Bear in mind that almost every one of the Windows 8 touch actions, such as swiping to expose the charms bar, has a corresponding hotkey. (For the charms bar, it's Winkey+C -- C for charms, get it?) You can find a rundown of all the different hotkey combinations here. If you just need access to the different bits of functionality that the various Windows 8 touch actions expose, you can perform most of them through key combinations.
Most desktop systems aren't touch-equipped. This will change as touch becomes a ubiquity not only for specific PC form factors (notebooks, convertibles, etc.) but for PC peripherals as well (monitors with touch included, for instance). We will also see more elegant integration of touch interface support into host OSes in VMs, but for now, workarounds to Windows 8 touch on desktops do exist.