For loop and boolean expression in it and other troubles..

[SilverWarior]

There are just so many things to check for. Ex: if selection is negative or positive, how many selector blocks there are in total etc..

You can solve this easly by sorting X1 and X2 so that X1 is alyways lower. Same goes for Y1 and Y2.
The number of selector blocks rendered only depends on trimmed selection dimensions.