Chap 7 ClippingHidden Surface Removal(1).pptVIP

* * * * * * * 3D clipping 三维裁剪 裁剪对象：线裁剪、面裁剪 裁剪窗口：规范的立方体、视域四棱锥 Sutherland-Cohen、梁友栋-Basky裁剪等算法都可以推广到三维情形 * On 3D transformation and clipping 何时裁剪? 投影之前裁剪——三维裁剪 优点：只对可见的物体进行投影，提高消隐效率 缺点：三维裁剪相对复杂 投影之后裁剪——二维裁剪 优点：二维裁剪相对容易 缺点：需要对所有的物体进行投影变换 * 三维裁剪实例 * 三维裁剪窗口的规范化 为什么引入规范视域体 简化投影 简化裁剪 规范化变换 将任意视域体变换成规范视域体的变换 * 三维裁剪窗口的规范化 y x -z 平行投影 y x -z 透视投影 两种规范化的视域体 平行投影：[0,1]?[0,1]?[-1,0] or [-1,1]?[-1,1]?[-1,0] 透视投影：[z,-z]?[z,-z]?[-1,zmin] * 总结 裁剪 二维线裁剪 二维多边形裁剪 文本裁剪 三维裁剪 关于三维变换与裁剪 * * * * * * * * * * * * * * * * * * * * * * * * * * Clipping and Hidden Surface Removal Li Guiqing South China University of Technology * Agenda Clipping (Textbook: chap 6, Sect. 6-7, 6-8) Terminologies Line clipping Polygon clipping Hidden surface removal * Agenda Clipping (Textbook: chap 6, Sect. 6-7, 6-8) Terminologies Line clipping Polygon clipping Hidden surface removal * 三维变换流程图(Recall) 局部坐标系 世界坐标系 视点坐标系 图像坐标系 规格化设备 坐标系 屏幕坐标系 造型变换 取景变换 投影变换 设备变换 视窗变换 二维裁剪？ 三维裁剪？ * Agenda Terminology Line clipping Polygon clipping * Clipping(裁剪) Determines the portion of geometric objects inside given region (2D或3D裁剪窗口). Applied to antialiasing(反混淆), hidden lines and surface, shadow(阴影), and texture (纹理) algorithms * Extensions of Clipping(裁剪) Polyhedron Polyhedron, Boolean operations Biermann et al. sigraph 2001 * Clipping algorithms(裁剪算法分类) Dimension of clipping windows：2D、3D Shape of clipping windows：regular(矩形、六面体) irregular(任意多边形和多面体) Objects to be clipped：points, lines, polygons, polyhedra, surfaces. Implementation：software/hardware * Agenda Terminology Line clipping Polygon clipping * 2D clipping (二维线裁剪) Determine which portion is in the region The portions in the window are preserved for displaying, and others are discarded In a typical scene, there are a great amount of clipping operations. Therefore efficiency is quite key. * 2D clipping: examples * Algorithms for 2D clipping Sutherland-Cohen 裁剪：编码 Midpoint clipping：除以2，移位运算 Parametric clipping and Liang(梁友栋)-Barsky 裁剪：高效率的裁剪 Nicholl-Lee-Nic