基于真实感雾效混合的快速渲染算法

A Fast Rendering Algorithm Based on Realistic Fog Effect Mixing

针对目前基于经验模型的雾效真实感不足和基于物理模型的雾效延时的问题,提出一种雾效混合算法改善雾效绘制的真实感和实时性.首先采用经验模型模拟基础雾,引入能见度因子和温度系数优化雾效衰减公式,使得平流雾、辐射雾、层次雾、体积雾的雾效公式得到统一,从而丰富雾效的多样性;其次引入Simplex噪声和风速完善边界噪声模型,克服传统雾效的规律性,优化雾的动态效果;再利用物理模型补偿细节,采用拉格朗日方法模拟细节雾,通过引入谐波叠加法建立风场模型,改善雾粒子运动轨迹,提升雾效的真实感;改进时间轴算法解决雾效颜色不随时间变化的问题,获得随时间渐变的动态雾;最后根据Henyey-Greenstein相位函数近似求解Mie散射,利用纹理和billBoard技术快速渲染雾粒子,并将基础雾和细节雾混合生成逼真的混合雾效.在GPU仿真环境下搭建不同雾场景,根据混合雾与传统算法在主观视觉与客观帧率方面对比作为评判指标,实验结果表明,该算法在保证至少40帧的基础上,绘制出细节突出的多种类雾效.

Due to shortage of the realistic fog effect with the empirical model and the delay problem with the physical-based model,a combined fog simulation algorithm is proposed to improve the reality and real-time performance.First,the empirical model is adopted to simulate the basic fog,and an optimized fog formula is unified to compute the advection fog,the radiation fog,the layer fog and the volume fog by introducing the visibility factor and temperature coefficient.The unified formula enriched the diversity of fog effects.Secondly,the Simplex noise and the wind speed are introduced to improve the boundary noise model.The method overcomes the regularity issues of the traditional effect and optimizes the dynamic fog effect.Thirdly,the physical model is used to compensate the details.The Lagrangian method is used to simulate the details of the fog,and the wind field is established by the harmonic superposition method to improve the movement path of fog particles and to enhance the realistic effect.And also,the improved timing axis algorithm solves the unchangeable fog color problem to obtain gradually changeable fog effect with time.Finally,the approximate algorithm of the Mie scattering is calculated according to the Henyey-Greenstein phase function,and the fog particles are quickly rendered with the texture and billBoard technology.Then,the base fog and the detail fog are blended to generate realistic fog effort.Different simulation scenes are built on GPU.The comparison between the blended fog effect and the traditional effect is judged by the subjective effect and objective frame rates.Experimental results show that the algorithm simulates a variety of fog effect with outstanding details on the basis of the frame rates no more than 40.