A Real-Time Adaptive Ray Marching Method for Particle-Based Fluid Surface Reconstruction

Abstract

In the rendering of particle-based fluids, the surfaces reconstructed by ray marching techniques contain more details than screen space filtering methods. However, the ray marching process is quite time-consuming because it needs a large number of steps for each ray. In this paper, we introduce an adaptive ray marching method to construct high-quality fluid surfaces in real-time. In order to reduce the number of ray marching steps, we propose a new data structure called binary density grid so that our ray marching method is capable of adaptively adjusting the step length. We also classify the fluid particles into two categories, i.e. high-density aggregations and low-density splashes. Based on this classification, two depth maps are generated to quickly provide the accurate start and approximated stop points of ray marching. In addition to reduce the number of marching steps, we also propose a method to adaptively determine the number of rays cast for different screen regions. And finally, in order to improve the quality of reconstructed surfaces, we present a method to adaptively blending the normal vectors computed from screen and object space. With the various adaptive optimizations mentioned above, our method can reconstruct high-quality fluid surfaces in real time.