Probability – How to find the joint cumulative distribution function in this region?

Find the cumulative cumulative distribution function of

$ f (x, y) = begin {cases} 1 & 0 the x the 1, 0 the y the 1, 2y the x \ 0 & text {otherwise} end {cases} $

If I use the definition $ F (x, y) = int _ {- infty} ^ x int _ {- infty} ^ y1 dudv $ for all $ (x, y) in mathbb {R} ^ 2 $.

How do I define regions?

It's easy to show that for the region $ x <0, y <0 $ then $ F (x, y) = $ 0but I have trouble defining other regions.