Evaluate along the straight line segment lying along x + y = 1

Now i take that i must paramaterize this.

x = t

y = 1 - t

dx = dt

dy = -dt

so my integral is now of (t - (1-t)i)(dt + idt)or something

so my question is, do i evaluate this from i to 1 ?

or from 0 to 1?

I'm not sure