Based On The Construction Of The Npr Technology Cad System

As the CAD systems are commonly used in many domains, demands for CAD are more and more higher. It is important and necessary to improve the current CAD system. The researchers turn their research emphases from pure modeling design to the design process itself while trying to find the best joint of the CAD system and practically creative design process. To the CAD system, its main concern is aiding design, which requests that the displaying technology could handle the designer's intension and provide the corresponding feedback so that the designer can make evaluation timely. In this regard, the traditional photorealistic rendering is not appropriate in many fields such as scientific illustration and architecture design: it can't communicate complex information in a comprehensible and effective manner. So, a new mechanism is necessary.We bring up a scheme to solve these problems: non-photorealistic rendering. The non-photorealistic rendering (NPR) is an approach that seeks to provide alternative method for rendering 3D models or reference image. It is easy to modify and capable of abstracting away details and clarifying shapes, so the demand of the clientele could be met by this means.This paper describes a CAD system, which can generate pen-and-ink illustration. The overall goal of the system is to enable user to easily generate effective and attractive illustration directly on a computer.The paper presents an overview of CAD and Non-photorealistic Rendering techniques and the pen-and-ink illustration techniques are discussed in detail. Because the differences between non-photorealistic rendering and the traditional photorealistic rendering, according to the feature of Non-photorealistic Rendering, we present a novel rendering architecture. In order to support the rendering architecture and to improve the stability and efficiency, our comprehensive strategic plan is focused on the basic areas of computer graphic: we present the design and implementation of modeling, system architecture and renderingWe propose a Shader based multiple passes rendering model towards computer-generated non-photorealistic rendering system. Techniques concerning coordination between multiple passes and illustration of textures and tone through strokes are described in detailed. Through this means, expressive ability of the system got significantly enhanced. Moreover the manipulating objects are surfaces and lines, which can let the users design more directly and habitually. Examples illustrated in pen-and-ink, demonstrating the capabilities of presenting 3D scene are also given in this paper.To support the Shader language, system design and to get attractive rendering result, a brief description of some of the salient features and terminology of hand-drawn pen-and-ink illustration are presented. Discussions of the stroke model, texture model, the stroke database, texture database, the frame of Shader and so on are also given in this paper. On the implementation of Shader language, the syntax rule and lexical rule are presented and an interpreter, which interprets and executes the Shader language, is also given.