How to create a line by mouse but in x and y direction only

i am working on a game which is basically coin matching game. i wanna draw

Step1: user starts as mention at image step2: user starts drag and as user drag line start draw but user can only draw in x,y plane direction not in angular direction as mention in image. step3: when user reach at specifice cell as shown in figure the line exits remains if it discountinues for some resons it disappears.