Large-scale forest rendering: Real-time, realistic, and progressive

Real-time rendering of large-scale forest landscape scenes is important in many applications, such as video games, Internet graphics, and landscape and cityscape scene design and visualization. One challenge in the field of virtual reality is transferring a large-scale forest environment containing plant models with rich geometric detail through the network and rendering them in real time. We present a new framework for rendering large-scale forest scenes realistically and quickly that integrates extracting level of detail (LOD) tree models, rendering real-time shadows for large-scale forests, and transmitting forest data for network applications. We construct a series of LOD tree models to compress the overall complexity of the forest in view-dependent forest navigation. A new leaf phyllotaxy LOD modeling method is presented to match leaf models with textures, balancing the visual effect and model complexity. To progressively render the scene from coarse to fine, sequences of LOD models are transferred from simple to complex. The forest can be rendered after obtaining a simple model of each tree, allowing users to quickly see a sketch of the scene. To improve client performance, we also adopt a LOD strategy for shadow maps. Smoothing filters are implemented entirely on the graphics processing unit (CPU) to reduce the shadows' aliasing artifacts, which creates a soft shadowing effect. We also present a hardware instancing method to render more levels of LOD models, which overcomes the limitation of the latest CPU that emits primitives into only a limited number of separate vertex streams. Experiments show that large-scale forest scenes can be rendered with smooth shadows and in real time. (C) 2012 Elsevier Ltd. All rights reserved.