Change the order of integrals..

$$\int_0^1dx\int_0^{1-x}dy\int_0^{x+y}f(x,y,z)dz$$

to$$\int dz\int dx \int f(x,y,z) dy$$

Not sure if to split the shape into two shapes, or do it directly. Either way i would like to know how its done..