In this article we discuss the applicability of global scattering functions for structure analysis of Grazing Incidence Small Angle X-ray Scattering (GISAXS) data. Contrary to rigorous analysis of the full 2-D detector image, which can be performed with complex simulation models, the global scattering functions described here will be used to model transverse detector scans in the $q_{\parallel}$ reciprocal scattering planes. In contrast to a full GISAXS analysis, this procedure cannot explain structural features perpendicular to the sample plane. The discussed method is useful for the analysis of weakly correlated films. These films are e.g. found in polymer inorganic composite materials based on commercially available nanoparticles. In hybrid material systems polydisperse structures, including particle aggregates without precisely defined shape are formed. The pictured approach, which models scattering in terms of structural levels, has been previously applied with success in conventional transmission SAXS geometry. It is based on conventional exponential and power laws. Hence, data analysis becomes less complex compared to simulation approaches. Here we examine if this unified fitting model can be used to model diffuse, non specular scattering resulting from GISAXS. In this context the applicability and limit of its application to diffuse scattering in the GISAXS geometry is discussed. Furthermore diffuse $q_{\parallel}$ scattering from different ideal particle types is simulated and compared with fitted results. To verify our approach, fit results from experimental GISAXS curves obtained for real samples are compared with results from Scanning Probe Microscopy and Scanning Electron Microscopy studies. The samples investigated range from evaporated Au films to hybrid TiO2/polymer films and demonstrate the usefulness in the structural analysis of complex films.