屏幕空间自适应的地形Tessellation绘制

Screen-space adaptive tessellation for terrain rendering

为了在大规模真实感地形渲染中利用GPU硬件加速的Tessellation技术,在对地形Tessellation原理分析的基础上,提出一种屏幕空间自适应的地形Tessellation绘制算法,实现了在GPU内部对地形模型的三角形自适应细分。该算法采用Tile和Patch的形式对地形数据进行分层组织,在CPU和GPU上分别以Tile和Patch为基础实现地形LOD(level of detail)的自适应简化;提出在Hull Shader上基于Patch边界的细分系数计算模型,确保了Patch细分时的无缝连接;给出了Domain Shader上置换贴图的处理过程,以实现细分顶点的高程纹理映射;并且采用了两级视锥体裁剪机制,减少了渲染数据的冗余量。实验结果表明,该算法具有较好的屏幕空间自适应性和渲染性能,能够在输入粗糙网格的基础上,渲染输出高分辨率几何细节特征的地形模型。

In order to render large-scale terrain on graphics processing units （GPU） using hardware-accelerated tessella- tion, a screen-space adaptive tessellation algorithm for terrain rendering is presented. The triangulation is performed entirely on the GPU, based on analyzing the principle of terrain tessellation. The proposed approach organizes the terrain data hier- archically by tiles and patches, which is the base for a terrain LOD simplification approach processed separately on the CPU and GPU. The edge-based tessellation LOD model for each patch is constructed to compute the tessellation factors in the Hull Shader for the water tightness surface. The procedure for terrain displacement mapping in the Domain Shader is de- signed to offset and transform each vertex height. Furthermore, a two-level view frustum culling mechanism is used to mini- mize the data to be rendered. The experimental results show that the algorithm has better screen-space adaptivity and ren- dering performance. It can produce the terrain model with high resolution geometric details in spite of inputting coarse trian- gle meshes.