  We introduce in this article a general formalism for Fourier based wave front
sensing. To do so, we consider the filtering mask as a free parameter. Such an
approach allows to unify sensors like the Pyramid Wave Front Sensor (PWFS) and
the Zernike Wave Front Sensor (ZWFS). In particular, we take the opportunity to
generalize this two sensors in terms of sensors' class where optical quantities
as, for instance, the apex angle for the PWFS or the depth of the Zernike mask
for the ZWFS become free parameters. In order to compare all the generated
sensors of this two classes thanks to common performance criteria, we firstly
define a general phase-linear quantity that we call meta-intensity. Analytical
developments allow then to split the perfectly phase-linear behavior of a WFS
from the non-linear contributions making robust and analytic definitions of the
sensitivity and the linearity range possible. Moreover, we define a new
quantity called the SD factor which characterizes the trade-off between these
two antagonist quantities. These developments are generalized for modulation
device and polychromatic light. A non-exhaustive study is finally led on the
two classes allowing to retrieve the usual results and also make explicit the
influence of the optical parameters introduced above.
