计算机图形学知识综述
CG复习总结Computer Graphics
Goals in Detail
Introduce basic concepts of computer graphics
Describe the 3D graphic representation flow in current PC
Describe some fundamental algorithms used in computer graphics
Introduce the computer graphics programming with OpenGL
Enhance the ability on programming and data structure exertion
Research in CG community
Contents
Survey of CG and Overview of Graphics Systems
Line/Circle Drawing algorithm
Polygon Fill Algorithm
Introduction to OpengGL Programming
Lighting model
Geometric Transformations
Clipping
Visible-Surface Detection
Graphics in “Computer Graphics”
是指由点、线、面、体等几何要素(geometric attribute)和明暗、灰度（亮度）、色彩等视觉要素(visual attribute)构成的，从现实世界中抽象出来的图或形
Tasks of CG
Generating 2D images of a 3D world represented in Computer by Computing, NOT by sensing.
(3D Models -> rendering -> 2D images)
Overview of the course
Geometry (Modeling)
– View, Transformation of Models (模型的投影和变换)
– Bezier Curves
– B-Spline Curves
– Triangle Mesh（三角网）
– Deformation （变形）
Rendering : photorealistic rendering and non-photorealistic rendering
– Basic Concepts, OpenGL
– Lighting （光照）
– Ray Tracing （光线跟踪）
– Acceleration of Ray Tracing（光线跟踪加速）
– Texture （纹理）
– Shadow （阴影）
– Radiosity（辐射度）
Research Hot Topics
• Rendering
• Computer Animation
• Geometry
• Video-based rendering
Geometric Transformation
Geometric transformation in 3D space
Translation(平移)
Scaling(放缩)
Rotation(旋转)
Homogeneous Coordinates(齐次坐标)
Global Transformation and Local Transformation
Projection
Perspective projection (透视投影)
Perspective projections in OpenGL
void glFrustum(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble znear, GLdouble zfar );
void gluPerspective( GLdouble fovy, GLdouble aspect, GLdouble zNear, GLdouble zFar );
Parallel projection (平行投影)
Clipping
Point clipping (点的裁减) ：是否在区域内部
Line clipping (线的裁减)
Binary Region Codes(区域编码) ：4-digit code CtCbCrCl（上下右左）
Mid-point Partition Algorithm（中点分割算法：二分）
Polygon clipping (多边形的裁减)
输出顶点为0~2.
Transformation from window to viewport
glFrustum函数和glViewport函数
Graphics Pipeline
图形学流水线可以概括为：
局部坐标的3D模型通过3D空间的几何转换得到全局坐标的3D模型，通过投影得到投影坐标系中的2D图形，通过窗口裁剪得到窗口坐标系中已裁剪的2D图形，通过窗口到视口的变换，得到视口坐标系中的2D图形，通过光栅化得到视口坐标系中的2D图像
Visibility Detection
Why to do it
Avoiding ambiguity (消除二义性)
Get the correct visual effect (正确绘制）
Improving rendering rates (提高绘制效率)
Back-Face Detection(后向面判别)
实现与平面法向的夹角V· N<0为前向面，V· N>0为后向面
Visible-Surface Detection Methods
Ray Casting Method（了解）：光线投射法
Z-buffer, Scan-Line Z-buffer（详细掌握）
stores a depth value for each pixel on the screen
Scan-Line Z-buffer:To process one scan-line of the screen at a time in order to reduce storage requirements
Area-Subdivision Method（了解）
Depth Sorting Method（整体掌握）
Lighting
Shading(着色)
Polygonal Shading
– Flat shading(平面着色)
– Interpolative shading(插值着色)：Interpolate color in interior
– Gouraud shading(高洛德着色 )
Face normal取平均得到vertex normal计算得到vertex color然后Interpolate colors across polygon
– Phong shading (different from Phong illumination)(Phong着色)
Interpolate normals rather than colors
Photorealistic Rendering Ray-tracing
• Introduction of ray tracing
• Ray intersection(光线求交)
• shadows(阴影)
• Transparence and specular reflection(透明和镜面反射)
• textures(纹理)
光线追踪的核心在于光线求交（Ray intersection）
The Simplest Ray Tracing：Ray Casting(光线投射)
Texture
Texture mapping(纹理映射) or texturing(贴纹理)
Texture usage
Texture acquisition(纹理获取)
Taking photograph
Procedure texture(过程纹理)
Texture synthesis(纹理合成)
Texture mapping(贴纹理)
Texture filtering(纹理滤波)
Aliasing(走样)和Anti-aliasing(反走样)
NPR stroke(非真实感绘制过程)
Let computer have partial or aggressively complete capability of artists, that is selectively rendering objects stylized and abstracted.（让计算机有艺术家的能力：抽象）
名词解释
Animation ：动画
Simulation ：模拟，仿真
Deformation ：变形
Triangle Mesh ：三角网
3D Data Acquisition and Modeling ：三维数据采集和建模
Color Space ：RGB、CMY、HSV、CIE XYZ
Diffuse ：漫发射
Ambient ：环境光
Specular ：高光（镜面反射）
Cathode ray tube(CRT) ：阴极射线管
Raster-Scan Display ：光栅扫描显示器
frame buffer ：帧缓冲（A memory area that image is stored in）
Resolution ：分辨率
OpenGL ：Open Graphic Library (开放的图形编程库)
Clipping ：剪裁
Composite Transformation ：综合变换
Depth overlaps checking ：深度重叠测试
Details
1、画出多个茶壶围绕中心一周
2、void glTranslatef(float x, float y, float z);如何使用，平移前的坐标是如何指定的？（移动整个物体）
x, y and z is the translation distances along the three axes.
3、void glRotate{fd} (TYPE angle, TYPE x, TYPE y, TYPE z);
绕vector(x,y,z)旋转angle角度
4、void glScale{fd}(TYPE Sx, TYPE Sy, TYPE Sz)
Sx，Sy，Sz分别为x，y，z变换的倍数
5、Local transformation can be implemented by inverse the multiplying order of the global transformation ：局部变换可以通过全局变换的逆乘法顺序实现（顺序完全颠倒即可）
6、Global Transformation and Local Transformation
Global transformation
每一次变换均可以看成是相对于原始坐标系执行的
后调用的变换矩阵乘在先前矩阵的左边
先调用的变换矩阵先执行
Local transformation
每一次变换均可以看成是在上一次变换所形成的新的坐标系中进行
后调用的变换矩阵乘在先前矩阵的右边
后调用的变换矩阵先执行
7、void glFrustum(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble znear, GLdouble zfar );
void gluPerspective( GLdouble fovy, GLdouble aspect, GLdouble zNear, GLdouble zFar );
两个函数的使用方法：
8、Z-buffer算法
Z-Buffer算法在像素级上以近物取代远物。面片在屏幕上的出现顺序是无关紧要的。
