布告板云树木模型的阴影快速生成与绘制

摘要

As an important visual feature of trees, shadows are very important for keeping the visual fidelity of the rendering result, and the shadow rendering speed affects the whole scene's rendering speed significantly as well. A tree shadow generation and rendering algorithm is proposed in this paper, which especially fits to the widely used Billboard Cloud tree model. Based on Shadow Map, the algorithm uses a depth transformation method to solve the self-occlusion problem of Billboards, and uses shadow map filtering together with screen shadow map filtering to render the soft shadow of trees. Besides, the graphics hardware function, i.e. Multi Render Target (MRT), is used to optimize our algorithmic procedure. Finally, the algorithm is tested by a tree model from SpeedTree, and the experimental results have shown that the shadow of Billboard Cloud tree model generated by our algorithm has good view fidelity and the algorithm is of high efficiency.%阴影是树木的重要视觉特征,对提高树木绘制的真实感具有重要意义,同时阴影算法的效率也是影响树木绘制效率的重要因素.文中针对树木建模中广泛应用的布告板云(Billboard Cloud)树木模型的特点,提出了BillboardCloud树木模型阴影快速生成与真实感绘制算法.在传统阴影图算法基础上,采用深度变换的方法解决了Billboard的自遮挡问题,使用阴影图滤波和屏幕阴影图滤波相结合的方法实现了树木软影效果,并利用图形硬件的多绘制目标功能对上述算法流程进行了优化,以提高算法效率.最后以SpeedTree树木模型为例进行了实验,结果表明,文中算法生成的Billboard cloud树木阴影真实感强,且具有较高的效率.