스택오버플로우에
http://stackoverflow.com/questions/4300399/android-drawing-a-line-to-follow-your-finger
http://stackoverflow.com/questions/2403604/fingertip-drawing-applications-on-android
api데모에 http://developer.android.com/tools/samples/index.html
s pen을 이용하는거라면
http://developer.samsung.com/s-pen-sdk
여기를 뒤저보시면 원하는게 있을겝니다.(샘플코드도....)