Real Time Shadow Rendering

Shadow is a very important visual cue to human. Shadow shows the geometry of the scene, emphasizes the spatial relationship between objects and moreover reveals the positions of light sources.Ideal point light source will generate shadow with notable edge, which is called hard shadow. Area light source will generate shadow with soft edge, which is called soft shadow. The first contribution of this paper is that we proposed a refracted under water shadow rendering algorithm which overcomes the deficiency that traditional hard shadow algorithms cannot handle refracted shadow. The second contribution of this paper is that we proposed a real time soft shadow algorithm which is suitable for real time applications.Common hard shadow algorithms fail to render under water shadow because water will refract the light. This paper introduces a fast algorithm for generating under water shadow based on GPU. In the proposed method, we generate shadow on the water surface using normal shadow techniques. Then we treat each shadow pixel as the point light source which shoots ray into the terrain. We use a simplified refraction formula to accelerate the calculation of refracting rays and we approximate the intersection point of refracting ray and terrain. This algorithm takes the advantage of the parallel pixel processing functionality of GPU. Experimental result shows that this algorithm can generate visually plausible underwater shadow under high frame rate (70~80fps). Moreover, this algorithm can be easily integrated into existing shadow rendering process, thus it is very suitable for applications such as 3D games which requires critical real time performance.Moreover, this paper proposed a real time soft shadow algorithm. Because Most soft shadow rendering algorithms have to consider the geometry of area light sources and occluders at the same time to generate shadows physically correct, they require huge amount of computation and run just at interactive rates even on high-end graphics hardware, thus not suitable for applications such as 3D games which require critical real time performance. This paper introduces a fast soft shadow rendering algorithm which utilizes parallel pixel processing functionality of GPU. It samples the shadow map parallel and produces soft edges to generate visually plausible shadow. Although it is not physically correct, experimental result shows that it can generate visually plausible shadow at real time (20fps). So it can be used in applications which are not sensitive to physical error on shadow but requires critical real time performance with good visual effects.