Point-Based Visualization of Metaballs on a GPU

Abstract

In this chapter we present a technique for rendering metaballs on state-of-the-art graphics processors at interactive rates. Instead of employing the marching cubes algorithm to generate a list of polygons, our method samples the metaballs’ implicit surface by constraining free-moving particles to this surface. Our goal is to visualize the metaballs as a smooth surface by rendering thousands of particles, with each particle covering a tiny surface area. To successfully apply this point-based technique on a GPU, we solve three basic problems. First, we need to evaluate the metaballs’ implicit function and its gradient per rendered particle in order to constrain the particles to the surface. For this purpose, we devised a novel data structure for quickly evaluating the implicit functions in a fragment shader. Second, we need to spread the particles evenly across the surface. We present a fast method for performing a nearest-neighbors search on each particle that takes two rendering passes on a GPU. This method is used for computing the repulsion forces according to the method of smoothed particle hydrodynamics. Third, to further accelerate particle dispersion, we present a method for transferring particles from high-density areas to low-density areas on the surface.