Real-time rendering of colour-shift effect of metallic materials

The directional-dependent effects of the materials are responsible for our perception of certain materials being realistic or not. Some materials consist of colour pigments, and these cause directional-dependent colour variations (or colour-shifts). For instance, we can observe a colour-shift effect of metallic materials, which means the changing of colour from metallic colour to pigment colour depending on the direction of incident illumination and direction of view. The most common criticism of existing analytical Bidirectional Reflectance Distribution Function (BRDF) models is that these models are inadequate to generate colour-shift effect of materials for realistic real-time rendering. This paper introduces a visually plausible shading model to generate colour-shift effect of metallic materials by modifying specular component with illumination and view dependent sheen. The developed shaders have intuitive parameters, which can generate different kinds of metallic effects for real-time rendering, including visually plausible gold, brass, silver, bronze and copper effects for real-time rendering.