关键词: 间接光照, 全局光照, 真实感绘制, 概率模型, 树木绘制

Abstract: After the sunlight shines on tree crowns, it will be reflecting and refracting among leaves and develops into indirect illumination effect. It is quite difficult to make fast simulation of such indirect illumination, when doing realistic rendering of trees. Traditional way of calculation, including light trace and radiancy, costs more time, which is hard to meet the demand of timing. This paper adopts a model of probability to quickly assess indirect illumination effect among leaves which enables to realistic rendering of indirect illumination effect. It establishes a bounding volume and assumes that the location and normal of the leaves in the bounding volume are generally in line with even distribution. It sets up reflection coefficient and transmission coefficient for the front and back of the leaf, as well as the attenuation function to describe the attenuation function of sunlight that travels through the leaf. Based on the bounding volume model with even distribution and the material properties of leaves, emergent light from the surface of each leaf will be calculated. As for the leaves with P center, indirect illumination effect caused by sunlight passing through neighboring leaves is able to be quickly calculated. In order to further improve rendering efficiency, it does not take traditional tree model with large amount of patches, but adopts a concise 3D tree model with trees and branches based on Billboards structure. It tactfully combines above-mentioned probability model with such presentation to complete the realistic rendering with indirect illumination effect.

Key words: indirect illumination, global illumination, realistic rendering, probabilistic model, tree rendering