GPU-based Real-time Rendering Techniques For Large-scale Point-based Models

Point-based graphics is a new research field of computer graphics. Because of the advantage and application of point-based rendering, rendering techniques for pint-based models hava become a hot topic for research in recent years. In this paper, GPU-based real-time rendering techniques for large-scale point-based models are discussed, including photorealistic rendering (such as lighting, texture mapping), non-photorealistic rendering (such as stylized silhouette rendering, stippling with silhouettes, emboss effect, cartoon, etc.) and other special effects (such as depth of field, motion blur, soft-edge shadow rendering).Firstly, point-based rendering and programmable graphics hardware techniques are summarized, and photorealistic-rendering techniques for point-based models, including lighting, texture mapping, are introduced in detail in this paper. Because of the limited efficiency of current Phong Splatting and ray-tracing techniques, we propose an efficient method for real-time lighting and material rendering of large-scale point-based models based on QSplat algorithm and GPU-based computation of illumination. So the balance of quality and efficiency is achieved. Two common methods for texture mapping of point-based models are analyzed. One is triangulation and texture mapping of point cloud, and the other is parameterization and texture mapping of point-based surfaces. Parameterization is needed in the two methods, so the computation is complex and the efficiency is not high. An efficient method for texture mapping of large-scale point-based models using GPU-base procedural textures is proposed in our paper, and real-time interaction can be achieved. Several examples of procedural texture mapping are also shown, such as wood texture mapping, checker texture mapping, dapple texture mapping, knitting texture mapping, etc.Afterwards, non-photorealistic rendering of point-based models is specially discussed in this paper. Non-photorealistic rendering techniques, including current research status of point-based NPR, are briefly described at first. The disadvantages of several current methods for silhouette rendering and stylized silhouette rendering of point-based models are specially analyzed, such as the object-space based two-pass rendering in Xu's method, the image-space based pixel linking, silhouette trimming and part silhouette missing in Zakaria's method. Because these methods cannot achieve real-time rendering, we propose an efficient method for stylized silhouette rendering of large-scale point-based models. In our method, silhouettes are computedbased on object space, and the one-pass post-filtering processing is applied to the image from the frame buffer. Several stylized rendering effects can be achieved, such as silhouette rendering in loose style, emboss effect, etc. By taking advantage of LOD structures in point-based rendering, such as QSplat etc., we also achieve stippling with silhouettes in one-pass rendering in low-level detail.Finally, several special effects of point-based rendering, such as depth of field, motion blur, and shadow, are discussed in our paper. Because of the low efficiency of current methods, the computation of depth blurriness based on GPU and the post-filtering processing are used in the implementation of our DOF method for large-scale point-based models. And the motion blur effect of large-scale point-based models is simulated in real-time by blending between previous and current frames that is similar to several-pass rendering method. Besides, the PCF technique is used to render soft-edge shadows of large-scale point-based models. At the same time, the implementation of algorithms, experiment results and high efficiency are also shown.