Using the Swype keyboard on Android devices is an efficient way to type faster with just sliding your fingers over letter and let the prediction mode do the rest.
On HTC devices, including HTC One M7 and HTC One M8 the Trace Keyboard functions exactly the same as Swype keyboard, and you need to do as follows to enable continuous input mode on your device:
1. Open Settings app and go to Language & Input
2. Under Keyboard & Input Methods, touch "HTC Sense Input"
3. Find the Track Keyboard option and enable it
4. Now you just need to slide your finger over letter to enter text
You can also change the Trace Color, by going to the Advanced menu and changing the color from the "Trace color" menu. The default color is Yellow.