Occlusion Map 遮挡贴图 Standard Shader系列12

Occlusion Map 遮挡贴图

本文档主要是对Unity官方手册的个人理解与总结（其实以翻译记录为主：>）
仅作为个人学习使用，不得作为商业用途，欢迎转载，并请注明出处。
文章中涉及到的操作都是基于Unity2018.3版本
参考链接：https://docs.unity3d.com/Manual/StandardShaderMaterialParameterOcclusionMap.html

The occlusion map is used to provide information about which areas of the model should receive high or low indirect lighting. Indirect lighting comes from ambient lighting and reflections, and so steep concave parts of your model such as a crack or fold would not realistically receive much indirect light.
遮挡图用于提供关于模型的哪些区域应该接收高或低的间接光照的信息。间接照明来自环境照明和反射，因此你的模型的陡峭凹面部分，如裂缝或褶皱，实际上不会接收到太多的间接照明。

Occlusion texture maps are normally calculated by 3D applications directly from the 3D model using the modeller or third party software.
遮挡纹理图通常由三维应用程序直接从三维模型中使用建模器或第三方软件计算得到。

An occlusion map is a greyscale image, with white indicating areas that should receive full indirect lighting, and black indicating no indirect lighting. Sometimes this is as simple as a greyscale heightmap, for simple surfaces (such as the knobbly stone wall texture shown in the heightmap example above).
遮挡图是一种灰度图像，白色表示应该接收全部间接照明的区域，黑色表示没有间接照明。有时，对于简单的表面，这就像灰度高度贴图一样简单(例如上面的高度贴图示例中显示的多瘤结的石墙纹理)。

At other times, generating the correct occlusion texture is slightly more complex. For example, if a character in your scene is wearing a hood, the inside edges of the hood should be set to very low indirect lighting, or none at all. In these situations, occlusion maps will be often be produced by artists, using 3D applications to automatically generate an occlusion map based on the model.
在其他时候，生成正确的遮挡纹理稍微复杂一些。例如，如果一个角色出现在你的场景中正戴着头巾时，头巾的内侧边缘应设置为非常低的间接照明，或者根本没有照明。在这种情况下，遮挡贴图往往由美术制作，利用3D应用程序根据模型自动生成遮挡贴图。

This occlusion map identifies areas on a character’s sleeve that are exposed or hidden from ambient lighting. It is used on the model pictured below.
这个遮挡贴图识别角色套筒上暴露或隐藏在环境光下的区域。它用于下图的模型。

Before and after applying an occlusion map. The areas that are partially obscured, particularly in the folds of fabric around the neck, are lit too brightly on the left. After the ambient occlusion map is assigned, these areas are no longer lit by the green ambient light from the surrounding wooded environment.
在应用遮挡贴图之前和之后。部分被遮挡的区域，尤其是颈部周围面料的褶皱部分，在左侧被照得太亮。在环境遮挡贴图被赋值之后，这些区域不再被来自周围树木繁茂环境的绿色环境光照亮。