Part 6 - collision detection "player vs snowball"

calculating the collision based on distance between the centre point player sprite and snowball (not pixel-level collision masking individual pixels of sprites, just two "virtual circles", when overlap = collision)

When collision happens, the code will add extra "sparks" sprite over the snowball, and change palette offset of the main character.

(the effects are for debug/educative purposes, probably not to remain for final version)