Rendering Method for Flat Origami

In flat Origami (Origami which is folded flat), some cases exist that have a closed-loop in the overlap order of faces after they are folded. It is difficult to display this shape correctly on the screen when Origami is expressed by sets of plane polygons of zero thickness as is generally used in CG because all faces are placed on the same plane. In the present paper, we propose a new rendering technique to solve this problem. In the proposed method, we prepare a matrix that represents the overlap relation between two faces and a face ID buffer, the concept of which is similar to a Z buffer in the z-buffer algorithm. With this buffer, the face located in the uppermost is monitored in each pixel at the rendering stage. We render the shape on the face ID buffer using a scanline algorithm and display the folded shape by outputting the result in which the edges are extracted. Moreover, we render the shape in technical illustration style by coloring each vertex according to the number of mountain and valley folds connected to the vertex. In addition, we propose a simple pseudo shading algorithm.