Research On Real-Time Soft Shadow Algorithm Based On Visibility Map

Shadow is an important technology to enhance the computer virtual reality. Shadow effects play an important role in 3D games. It is necessary to military simulation filed. It is much more realistic and vivid if adding shadow to 3D scene. High-quality shadow effects, not only make the virtual scene closer to the real world, but also provide more rich information to it, such as shadows can reflect the relative distance of light, occlusion body and receiver. The size and shape of the shadows can reflect the attributes of geometry and surface of the occlusion body and receiver in the scene.Shadow computation is mainly including image-based and object-based algorithms. The advantages of image-based algorithms are the ability to quickly generate interactive shadows, and independent of the scene complexity, but with the disadvantages of aliasing, etc. Object-based methods are directly to analyze the scene to generate high-quality and accurate shadows, but they are not suitable for rendering real-time shadows because of high complexity.As a classical image-based technology, the shadow map can generate shadows which only need two paths for rendering. In this paper, we carefully study and analyze the shadow map and its series of improved algorithms, and summarize the general expansion technical route of it.Real-time shadows and soft shadows are the shadows with high-quality which need a lot of calculations. The traditional shadow maps can only generate hard shadows. This paper proposes bivariate attenuation function during the process of shadow map generation to expend the traditional shadow map. Fisrt of all, generating the shadow width and shadow depth map, and then constructing attenuation function, computing adjustment factors, adjusting the brightness of pixel and generating shadows. There are some problems when simulation soft shadows for a single sample point, such as aliasing. This paper also proposes visibility map algorithm for shadow generation. Sampled by the light source, generate a visibility map for the scene. The map stores visibility relative of each pixel with light source, and then adjusting the brightness of pixel using visibility to generate the final shadow.The two methods can achieve perfectly real-time performance by the rapidly computing ability of GPU. The borders of shadows also have good softness.