Real-Time Rendering of Old Glass Panes

Many cultural heritage projects involve the 3D reconstruction of old glass buildings. Old glass, however, has many defects, due to the artisanal manufacturing techniques of the time, such as crown or cylinder blowing. The presence of these defects has a number of visual consequences, manifesting itself in the deviation of light passing through or reflecting off the glass panes. The appearance of these old glasses, the lighting produced through their surface, and the vision of the world perceived through them, is thus very different from what is perceived through contemporary industrial glass, and therefore has a considerable impact on the rendering that will be produced in their presence. However, setting up interactive virtual tours that take into account these old glasses is proving complex, as the materials available in commercial 3D rendering engines are unable to faithfully reproduce the lighting effects produced. In this paper, we propose a precise, real-time rendering of the surface and volume defects (bubbles, chords) present in some old glass and their impact on the appearance of the world perceived through these panes. Our approach is based on ray tracing, which not only interacts with the material's geometric defects, but also takes into account the curvature of light as the glass's refractive index varies.