The form of a building is among the most critical design aspects concerning building energy consumption. Form-based passive design strategies, like solar control, can significantly reduce heating and cooling demands if implemented early in the design process. In this sense, there is an evident need for tools that can adequately support designers in their decisions. This paper aims to illustrate how geometry-based graphical methods (GGM) can provide effective support in the conceptual design stage. The paper introduces a novel digital framework for designing and analysing shading devices that leverages geometrical models and graphical methods. The digital implementation of GGM allows extending their applicability to three-dimensional and non-planar geometries. A comprehensive review of existing methods and tools for the design of shading devices lays the ground for the proposed digital framework, which is then demonstrated through two case studies. The results show that the diagrammatic nature of GGM facilitates a better and more direct understanding of the relationship between form and performance.