A. Using Triangle Shell Technique to Render Silhouette Outlines Considering the controllability of line thickness and the convenience to implement on GPU, triangle shell technique is used in this paper to extract silhouette outlines from 3D models. The steps of triangle shell technique are described as follow: a) Enable Z Write, cull the back faces of the model, and render it in a normal way. b) Create a second surface by shifting the surface along its vertex normals. c) Cull the front faces of the model, enable Z Test, set condition to "less or equal", then render it in black. Fig. 2 shows the silhouettes rendering process of a blue ball using triangle shell technique. In fig. 2(b), we can see that only the visible hemisphere of the original model is left because the back faces were culled out. In fig. 2(c), a black hemisphere whose front faces were culled out, is added into the picture. Fig. 2 (d) is the