Main benefits are summarized below:
- Due to the nature of the point-based approach, the resulting ambient occlusion effect is smooth.
- Displacements, a costly operation in the ray-tracing case, come at no additional cost in the point-based method.
- No need to declare objects visible to the ray-tracer, this can save a lot of memory.
The drawbacks of point-based occlusion can be summarized in the following points:
- It is an approximation to the real occlusion. In general, the obtained occlusion is darker than the ray tracing case and it is necessary to adjust quite a few parameters to obtain the same look. More about parameter adjustments in Algorithm Control Parameters.
- The pipeline is obviously more complicated since one need a special pass to create the point cloud(s).
上述摘自3delight 文档
ao 效果更smooth
对置换支持更快更高
避免光线跟踪，减少内存使用
ptc ao的不足：
与光线跟踪的ao相比，ptc ao只是近似计算的非真实ao，所以某些地方可能比raytrace的药黑，需要更多的调节参数才能达到一样的效果。
因为需要预先计算出ptc文件，所以流程和操作上稍微复杂。