The Speed of Clouds : Utilizing Adaptive Sampling to Optimize a Real-Time Volumetric Cloud Renderer

Abstract: Volumetric clouds are often used in video games in order to improve the realism or graphical quality of the game. However, in order to achieve real-time rendered clouds, optimizations have to be implemented as part of the rendering algorithm. These kinds of optimizations improve the performance, but can also have a negative impact on the visual quality of the clouds. This thesis investigates the use of bilinear interpolation for the purpose of improving the performance of a volumetric cloud renderer, while trying to avoid any substantial reduction in visual quality. This is extended by looking at the effect of adaptively sampling the pixel colors. The renderer itself is created in Unity3D using a ray marching algorithm. As part of the literature study, this research also explores different ways of measuring visual quality within real-time rendering. As a result of this, the thesis uses the Structural Similarity Index Measure to measure the visual quality. The research found that utilizing bilinear interpolation to ray march every eighth pixel results in a performance gain of 45%. However, it also reduces the visual quality of the volumetric clouds. This is counteracted by using adaptive sampling to interpolate only where the standard deviation of pixel colors is below a threshold. We cannot, however, determine the optimal value of this parameter, since it depends on the requirements of the renderer. Instead, it has to be determined on a case-by-case basis.