I am not sure about the meaning of the phrase "slide two fingers across the screen" in the following sentence:
In N.O.V.A. you can slide three fingers over a door to open it, slide two fingers across the screen to toss a grenade or draw a targeting box around an enemy.
Does the phrase above mean to slide anywhere on the screen? Or does it convey a particular direction? Being a non-native speaker, I cannot figure out the exact meaning the word "across" here. The Merriam-Webster defines across as from one side to the other side of (something). Does it mean that in the given context the word "across" does not involve any particular direction, like up-down?