The Research On Shader-Based Real-Time Cartoon Rendering

NPR (Non-Photorealistic Rendering) is one of the hotspots of current Computer Graphics research. Cartoon Rendering is an important researching area in NPR. The algorithm of Cartoon Rendering reflects some pivotal themes and technique of NPR. Programmability is the mainstream of current display hardware development. Real-time Cartoon Rendering has a wide application in current film entertainment and video game industry. The exploration of using shader to implement real-time Cartoon Rendering algorithm is of great importance in both theory and application.Being similar to the traditional cartoon making process, the research is divided into two parts named painting and inking. This paper used three parts to describe the algorithm behind cartoon painting, inking and combination of these two parts, and the implementation of using resent shader technique.This paper discussed three methods in painting part: color index table, texture mapping method and dot3 shading. In color index table method, there is a color table with items of all colors used in scene. Each item in the table includes the highlight, diffuse and shadow area colors. The diffuse value of lighting mode will be used as the index into the table. Texture mapping method replaces the table with a texture and uses the diffuse value as the texture coordinate to sample the texture. Dot3 shading uses the diffuse value to calculate the width of surface color band and the edge dynamically and uses the specified color to shading them. The inking algorithm is grouped by 4 categories: surface angle silhouette, procedural geometry silhouette, image-based outlining and direct drawing method. Surface angle silhouette is based on the fact that the diffuse value at the edge is nearly zero. This method uses texture to render the silhouette. Procedural geometry silhouette method draws front faces first and then back faces to make the silhouette visible. Image-based outlining uses the pixel shader as a effective image processing unit to process the G-buffers and then enhance the resulting image. Direct drawing method separate edge detection with edge drawing. This method is able to process a wide range of types of edges.In the combining part, the paper researches the combination of different kinds of painting and inking algorithms. The texture mapping method can be use in both painting and inking. Procedural geometry silhouette, image-based outlining and direct drawing method can be combined with any kinds of painting method but each of them need some special process and skills to do that.Based on a real project, the author explores and summarizes the real-time Cartoon Rendering algorithms, and did research and experiment on using the shader to implement part of them. At the conclusion of this paper, we compare and analyze the image quality and running efficiency of each painting and inking method. This can be a base and reference of application. The author also made the combination of the shader-based cartoon rendering method to the rendering engine of the project, and achieved the desired results.