7-游戏场景的几何优化.pdf

游戏场景的几何优化 II . LOD技术 II. 游戏场景的几何优化 • 层次细节技术（LOD-Level of Detail） – 简单取舍型LOD：不绘制投影尺寸小的物体，模型的出现和消失 造成跳跃感，造成视觉失真 – 平滑过渡型LOD：淡入淡出，适用于模拟小的植被、装饰物和家 具等 – 静态LOD：预计算同一个物体的多个不同精度版本，同样需要解 决过渡中的跳跃现象 • 雾化、融合 – 动态LOD：几何变形算法是否高效 • 基于顶点删除、基于边删除、基于面删除 II. Object Simplification Object is a set of vertices, edges, faces. We will present algorithms to simplify object by reducing its # vertices, and # edges. In reducing either #, we are actually reducing the number of triangles in turn. These algorithms are also known as simplification algorithms. Online vs Offline ? Manual vs Auto? 3 II.1. Vertex Clustering Observation: when an object is placed at some relatively far distance, many vertices when rendered to a window are actually collapsed into (i.e. projected onto) a same pixel. Thus, it is reasonable to generate simplified model, i.e. lower LoD model, by collapsing each group of nearby vertices into a single representative vertex. These representative vertices take the place of original ones, and they in turn create new triangles to replace the old ones. In the process, some old triangles are collapsed into an edge, or a representative vertex, or remain as triangles but with their vertices moved to representative vertices. 4 II.1. Vertex Clustering original model 1. grading 2. triangulation clustering resolution 3. clustering 4. synthesis 5. elimination 6. adjustment of normals 5 II.1 Vertex Clustering Process of Vertex