About non-box function ranges (also integral question)

Hi, i will need to make a integral of a bidimensional function in the space-phase
range, what means a non-box range. Using TF2 i cant find a way to define this
kinf of range. As a simple example i was trying to evaluate the area of 1/4 of circulus

A= int_0^1 int_0^{sqrt(1-x^2)} dy dx

How i do that if TF2::Integrate only gets numbers as parameters?

I will have to define my own integration function in a class derived from TF2?