【作者】 王健；

【导师】 冯月萍；

【作者基本信息】 吉林大学 ， 计算机应用技术， 2006， 硕士

【摘要】 基于点的绘制方法已成为近几年计算机真实感图形绘制研究的热点。与传统方法相比,该方法计算复杂度低,数据结构简单,造型手续简化,并且越是在复杂的场景中或者计算精度要求较高的情况下,该方法越能发挥它的优越性。本文对传统的真实感图形绘制方法进行了研究,分析了其中的缺点与不足,在此基础上提出了基于离散点的造型和绘制方法,并结合离散点造型的特点,在真实感图形生成过程中提出了新的方法,经过不断的实践和改进,在许多不同的场景中都取得了良好的效果。更多还原

【Abstract】 With the development of Computer Graphics and the computer itself,the realistic graphics have applyed broadly in our daily life, such ascomputer aided design(CAD), multimedia education, virtual realitysystems, scientific visualization, animation, film’s acrobatic simulation,computer games and so on.But there were increasingly stringentrequirements in the computer visual feeling, which need us to study morealgorithms of generating lifeliker realistic graphics.Currently the generating course of realistic graphics includes scene modeling,transformation of coordinate, frustum culling, removing hidden surfaces andcalculating illumination of visibility surfaces. Those processes need informationon the basis of graphics as a precondition. Only in the basis of graphicsinformation, we can dispose to graphics for deformation, shrinking,enlarging, and display. And the basic information here refers to thegeometric information and topological information. Traditional methodsuse a culmination table and a triangle table to store that informationseparately. Because the rendering unit is triangle and the number of thetriangles is usually twice more than the point’s, which result in a sharpincrease in the calculation and a lot of rendering time. So a large numberof scholars began to study a new rendering method that directly processedsurface points to gain efficient rendering speed. In such circumstances,people began to explore a new rendering method, and Point-BasedRendering becomes a new focuses.Point-based Rendering is modeling and rendering based on the points, aswell as some other processing.This rendering algorithm does not use thetraditional triangle facet method. It records the information of each point,and directly from the information it can reconstruct the image. Thus, itprovides a new approach that can resolve the difficulty of fast renderingof abundant 3D sample data.This paper has carried on research to the generating course of realisticgrapgics and has analyzed its shortcoming and insufficient. Then a kind ofnew method of modeling on the basis of discrete points is proposed. Themethod can avoid a large amount of operation of calculating points ofintersect. Because of its simple data construction, the operation of adding,deleting and modifying curved faces is very convenient. And because ofthe simple procedure of modeling, this method is suitable for showing thecartoon. The content of this text include modeling on the basis of discretepoints, transformation of coordinate, visibility, illumination, generating ofshadow, texture mapping and smoothing of image.PBR of realistic graphics used the discrete points of the object surfaceto model the entities shape. We used the data from the polygon meshmodel.We used polygon mesh transformation in scene modeling. For polygonmesh data, we only need its points and normal vectors. However, theinitial mesh data points are limited, so we used polygon mesh subdivisionalgorithm encrypt these in order to obtain sufficient density of data. Thesubdivision algorithm adopted Loop and Catmull algorithm to obtainmore polygon facets and points. Then, we realized the modeling on thebasis of discrete points.This paper designed three elimination algorithms by the character ofthe PBR: back-point elimination, based-view elimination and regionrelative depth elimination. The theory of back-point elimination is thatuse the angle between the vector in the view direction and normal vectorof each point to determine whether a point is a back-point or not;based-view elimination is due to some points on 3D objects may beprojected to the same pixel on the screen, these points form a sequenceaccording to the view direction. Each pixel has a point’s sequence(thissequence may empty). In the sequence, only the first point is visible, theother points are hidden. So we considered the first point when show andcalculate illumination;region relative depth elimination is projectedaiming at the problems of the above two methods, this algorithm got ridof the points should be hidden by frontal ‘surface’ through .relative depthin a small region. Experiments show the third method can remove hiddenpoints commendably.We introduced the transformation from world coordinate to viewcoordinate and Phong illumination. This illumination only considered thereflection of direct light and used ambient light denote the reflectionbetween objects.Because the distribution of discrete points is inequable, object surfacesappear holes or sawtooth or dot noises. The motive of the imagereconstruction is wiping off manual trace, sawtooth, pixel’s color steepchange on PBR and holes as a result of lacking information. This paperwe use the texture filtering interposition and smoothness processing toreconstruct the image. The filter method estimate whether the pixel isbackground and the lacking information bring holes or not, fill up theinformation by linearity interposition. Image smoothness is achieved by atemplate which is a local pixel field. We adopt a circular template whichcan wipe off wave noises and keep the intrinsic contrast.In the procedure of shadow, we compare several shadow algorithmsbased points. Combining the context point’s character, we project ashadow algorithm recur to Zbuffer. We transform the coordinate fromview vector to light vector, calculate the points according to z valuewhich are the most near distance to the light and produce shadow.Calculate the intersections between known plane and the line which fromlight to those points. These intersections are shadow.This paper achieved the 2D texture mapping from point to point. Weuse the points stored in Zbuffer corresponding to the texture points andsmooth the result image.更多还原