  We discuss the development of the new radiative transfer code Wind3D. It
solves the non-LTE radiative transport problem in moving stellar atmosphere
models in three geometric dimensions. The code accepts arbitrary 3D velocity
fields in Cartesian geometry without assumptions of axial symmetry. Wind3D is
currently implemented as a fully parallelized (exact) accelerated lambda
iteration scheme with a two level atom formulation. The numerical transfer
scheme is efficient and very accurate to trace small variations of local
velocity gradients on line opacity in strongly scattering dominated extended
stellar winds. We investigate the detailed formation of P Cygni line profiles
observed in ultraviolet spectra of massive stars. We compute the detailed shape
of these resonance lines to model local enhancements of line opacity that can
for instance be caused by clumping in supersonically expanding winds. Wind3D
will be applied to hydrodynamic models to investigate physical properties of
discrete absorption line components.
