It's a type cast. Basically, there are two kinds of "numbers" that computers use: integers (int) and floating point numbers (float). The "(float)" in in the line of code says that, even though the variable mouseX is an int, treat it like a float this one time so that when you do division, you get a float back instead of an int - basically, it's there to avoid truncating the result of the division to a whole number.