pnl_temp.filter = (screen_size.x != HUD_reference.x);

Yeah, that works on the fly, because its a boolean operation. Uhm, or simplier explained: (screen_size.x != HUD_reference.x) returns only 1 or 0, so, these are also the only values .filter accepts.

The reason for this line, is, btw, that even when I scale it with 1 for both axis', it is blurry with filter=on. So, I simply turn it off and it is sharp as hell.

EDIT: you can do such things with every boolean property (=flags). But you can't assign them directly. You can use e.g.

boolean = sign(boolean);
or
boolean = (boolean == 1);

(this doesnt count for vars, there you can assign like every variable)

booleans (operations) are really useful, they are shortening the code a lot.