一种实用且鲁棒的模板阴影渲染算法
Practical and Robust Stenciled Shadow Volumes for Hardware-Accelerated Rendering
摘要：
25年前，Crow发表了确定场景中阴影区域的阴影体积方法。十年前，Heidmann描述了一种硬件加速的基于模板缓冲区的阴影体积算法。不幸的是，硬件加速的模板阴影体技术还没有被3D游戏和应用广泛采用，这在很大程度上是由于所描述的技术缺乏鲁棒性。尽管有广泛的硬件支持，这种情况仍然存在。具体来说，一直缺乏的是一种技术，鲁棒地处理各种“硬”的情况下创建的近或远平面剪切的阴影体积。我们描述了一个强大的，无伪影技术的模板阴影体积的硬件加速渲染。假设现有的硬件，我们解决的问题，否则所造成的阴影体积近，远平面裁剪，通过（1）将传统的远裁剪平面“在无限远”，（2）光栅化与无限阴影体积多边形通过齐次坐标，和（3）采用zfail模板测试计划的组合。深度箝位是NVIDIA GeForce 3提供的一种新的光栅化功能，它不需要将远平面放置在无穷远处，从而保持了现有的深度精度。我们还提出了双面模板测试，以提高渲染模板阴影体积的效率。
英文摘要：
Twenty-five years ago, Crow published the shadow volume approach for determining shadowed regions in a scene. A decade ago, Heidmann described a hardware-accelerated stencil buffer-based shadow volume algorithm. Unfortunately hardware-accelerated stenciled shadow volume techniques have not been widely adopted by 3D games and applications due in large part to the lack of robustness of described techniques. This situation persists despite widely available hardware support. Specifically what has been lacking is a technique that robustly handles various "hard" situations created by near or far plane clipping of shadow volumes. We describe a robust, artifact-free technique for hardware-accelerated rendering of stenciled shadow volumes. Assuming existing hardware, we resolve the issues otherwise caused by shadow volume near and far plane clipping through a combination of (1) placing the conventional far clip plane "at infinity", (2) rasterization with infinite shadow volume polygons via homogeneous coordinates, and (3) adopting a zfail stencil-testing scheme. Depth clamping, a new rasterization feature provided by NVIDIA's GeForce3, preserves existing depth precision by not requiring the far plane to be placed at infinity. We also propose two-sided stencil testing to improve the efficiency of rendering stenciled shadow volumes.
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