目的 模拟绘制焦散效果是真实感图形绘制的重要组成部分。利用可编程GPU硬件，基于图像的光子映射方法绘制速度快，但由于使用了近似采样和计算，会产生失真。为了克服这一现象，针对理想的镜面反射、折射体，提出一种快速绘制焦散效果的方法（VOBPBT）。方法 该方法首次定义了光子路径映射图的概念，并提出通过基于虚顶点光子映射的光子束跟踪来准确构建光子路径映射图的方法；此外，方法也创新性地提出利用光子路径映射图来查找焦散三角形，创建焦散映射图的方法。结果 实验结果表明，本文绘制结果真实，可以处理多次递归反射、折射，能够绘制连贯的高频焦散效果，同时可以达到交互的绘制性能。结论 本文VOBPBT方法在可交互计算机仿真、计算机游戏、虚拟漫游等应用领域具有一定的实用价值。

Objective Caustic rendering plays an important part in the research of photorealistic image rendering. Based on programmable GPUs, image-based photon mapping renders fast but suffers from artifacts caused by sampling and computing approximately. Method To overcome this drawback, this paper proposes a fast method called virtual object-based photon beam tracing (VOBPBT) to render caustic effects. VOBPBT originally defines the photon-path map and then constructs the map. It also presents a way to find caustic triangles in the photon-path map and splat them onto the caustic map. Result This method can recursively render reflective and refractive effects as well as high-frequency caustic effects realistically in an interactive speed. Conclusion VOBPBT is useful in interactive computer-aided simulation, computer games, as well as virtual tours.