大规模雪场景的实时绘制

摘要

大规模雪场景的真实感实时绘制在虚拟现实、雪灾的预防和救援、军事仿真及游戏设计等领域有着广泛的应用价值,但现有方法难以同时生成大规模动态雪场景的积雪及飘雪效果.为此提出并实现了一种交互式大规模雪场景建模与实时绘制的新方法.为了精细地模拟场景的积雪效果,提出一种基于视点的自适应降雪遮挡图模型,能在实时更新地物的遮挡关系的同时大大减少大规模雪场景中积雪的计算量,并提高了计算精度；对于场景的飘雪,采用一种基于视点的雪粒子分层建模技术来减少雪粒子数量,将视点变换及降雪粒子系统移至GPU中进行加速计算；采用动态多旋转纹理来模拟飘落雪花的形状以增加其真实感；采用几何与纹理混合绘制的方式来减少大场景的复杂度.最终成功地实现了野外和城市两个大规模雪场景的实时漫游,在场景中可看到压雪累累的树枝雪挂景象及轿车上厚厚积雪等冬天美景.%Real-time rendering of large-scale snow scenes with high realism has wide applications in the areas such as virtual reality,snowy disaster's prevention and rescue,military simulation and game design,etc.However,current methods cannot simultaneously simulate both the snow accumulation and falling effects for large-scale dynamic snow scenes.To solve this problem,we propose a new method of modeling and real-time rendering.To simulate the accumulation of snowflakes on different objects in the scene precisely,we present an adaptive occlusion map for the falling snowflakes,with respect to the object distribution within the current view frustum.The occlusion map will be updated in real-time allowing dynamic objects to be included in the scene.To simulate the huge amount of dynamically falling snow flakes,we adopt a view-dependent particles grouping technique to reduce the amount of the snowflakes,meantime move the view transform and evolution of snow particle system into GPU for acceleration.To enhance the realism of falling snowflake,we adopt a dynamic texture sequence of multi-rotary snowflake.Besides,a hybrid approach of geometry and texture is employed to render the distant view of large-scale snow scenes with less computation.Based on the above approaches,we successfully implemented the real-time walkthrough of large-scale snow scenes including both urban and suburb circumstances,and generate the beautiful winter view such as heavy snow accumulation on the tree branches and the covers of cars,etc.