Asymmetric Geometry Clipmap Algorithm

When it comes to the 3D graphics scene, we always classify it to two types: indoor graphics environments and outdoor graphics environments. Researchers have published different optimal rendering methods for these two kinds of scene. The key technique for outdoor graphics environments is the realtime rendering of mass terrain height-field data. To achieve this goal, level-of-details (LOD) control is applied to adjust the terrain geometry. Geometry clipmap is a novel regular mesh based algorithm which generates nested regular grids and updates only the newly exposed "L-shaped"region so that it can keep visual continuity and get high performance in fast movement. After having studied and implemented the geometry clipmap algorithm, we found that the factor deciding the frame rate is the size of clipmap. So we proposed the center-asymmetric geometry clipmap algorithm which generates center-asymmetric nested grids and makes progress in the first step of the geometry clipmap. Our algorithm offsets the center of each level of grids as a function of view direction parameters. Each level is composed with the new grids surrounding the center instead of the view point. After the update of the new exposed "L-shaped"region, we eliminate the gap caused by the power-of-two mismatch at boundaries by extending the clipmap with one cell around. Then we offer a uniform interpolation formula to fetch the height in coarser level. With the new features of graphics hardware, we implement geometry morphing and texture blending in GPU. Finally, because the grids of center-asymmetric algorithm are similar to the result of view-frustum culling, our method avoided view-frustum culling before rendering.