Fast and Flexible Tree Rendering with Enhanced Visibility Estimation

We present a set of techniques to simplify tree models for faster rendering while retaining their visual resemblance to the original model. This goal is achieved by setting a budget constraint of how many leaves shall be rendered, and we select leaves with higher possibilities to be visible to generate a simplified model for rendering. We first examine how leaf objects can be prioritized to provide a tree model suitable for a single viewing angle. The camera's projected screen space is partitioned into several small regions to ensure that each region is guaranteed to be filled with a certain number of leaves. Each region selects higher priority leaves by utilizing the leaf objects' spatial relationship to the camera. Then, an iterative algorithm is proposed to allocate leaf objects at different viewing angles. The algorithm chooses different viewing positions for leaf allocation at each iteration with the goal of maximizing the resemblance to the original tree model at all possible angles. Three criteria taken in consideration for viewing angle selection are: distance, leaf normal, and unfilled pixel. Experimental results are provided to demonstrate time efficiency of the proposed techniques at the cost of little visual degradation.