How to change my app resolution according to client display size ? For example, if someone have ultra wide or square display the app should fit perfectly according to the resolution of the display.

I stored the position of ball in ballX and ballY. But I don't know how to calculate dx and dy ?

Hey! I'm remaking Pong game with LOVE2D and Lua. Can someone tell me how can I make my ball move, give it a random angle and velocity ?
Github : https://github.com/imadityaksingh/Pong