In my game all objects are facing right direction by default but they can be rotated and one of my object (let's call it "shooter") needs to know if any object is on its line of fire. If so, it shoots... The most basic idea that comes to my head is to calculate the equation of a straight line, given the left bottom corner of the "shooter" and its right bottom corner. Then I could check if left top corner of some object is above the line and if its right bottom corner is beneath the line. If so, I'd say that it's on the "shooter's" line of fire. But I suppose that this could be done in a much simpler but maybe a little sophisticated manner. Unfortunately I'm not sure how... I would be grateful for offering some better approach!
Here's the drawing for clarity ^^: