A few years back I saw someone playing a game. It was on mobile and I have no idea what it is called. In the game you wound tap dots which were black. It looked really fast paced. Occasionally instead of a dot you would slide your finger along a line. It looked really cool and I have been trying to find it for weeks now. Help it's driving me insane!
There are several games like this in the Google Play store. Try looking at "Don't Tap The White Tile". It sound like what you are describing and is one of the more popular games of that style. If you need further help, /r/tipofmyjoystick is a great subreddit to figure stuff like this out.