Shadow Catcher

阴影捕手

Shadow Catcher

阴影捕手

To be clear upfront: The Shadow Catcher shader is simply a much easier and faster method of achieving the same effect that can also be achieved using other methods, e.g., with the Compositing tag, multi-pass tricks, etc.

首先要澄清的是: 阴影捕手着色器是一个简单而快速的方法，可以达到同样的效果，也可以通过其他方法来实现，例如，使用合成标签，多重过关等。

In short, the Shadow Catcher shader integrates shadows and, if desired, reflections into the Alpha channel.

简而言之，阴影捕捉着色器集成了阴影和，如果需要，反射到阿尔法通道。

Only shadows and/or reflections from objects to which shaders are assigned will land in the Alpha channel (the remaining space in the Alpha channel will be black).

只有阴影和/或对象的反射被赋予着色器将土地在阿尔法通道(剩余的空间在阿尔法通道将是黑色)。

This makes it easy, for example, to insert rendered objects in photos in a compositing program, i.e., insert them into a two-dimensional background (backplates):

例如，这使得在合成程序中将渲染的对象插入到照片中变得容易，也就是说，将它们插入到一个二维背景(背景)中:

The following conditions must be met:

必须满足下列条件:

1. The Shadow Catcher shader must lie on the object onto which the shadow or reflection is cast (this would be the black plane in the image above; a Floor object would also work just as well) 阴影捕捉着色器必须位于投射阴影或反射的物体上(这将是上图中的黑平面，地板物体也可以)
   
2. The 这个Alpha Channel 阿尔法通道 option must be enabled in the render settings’ 选项必须在渲染设置中启用Save 保存 menu 菜单
   
3. The lighting situation should match that of the background into which the rendered object will be inserted as closely as possible. In the image above, the light that casts the shadow should be positioned behind the figure to the right. Often, a second light source is used that creates a uniform environment light (somthing like 照明情况应该与背景相匹配，渲染的对象将尽可能近地插入其中。在上面的图像中，投射阴影的光线应该位于图像的右后方。通常，使用第二个光源来创建一个统一的环境光(比如Ambient Illumination 环境照明).
   
4. Render the scene. The saved image file can now be opened in a compositing program and inserted into a background image, where shadow and reflection will be displayed according to the Alpha channel’s settings. 渲染场景。保存的图像文件现在可以在合成程序中打开并插入到背景图像中，其中的阴影和反射将根据阿尔法通道的设置显示
   

Limitations

局限性

• Note that GI effects cannot be taken into account by the Shadow Catcher with regard to shadows since it only works with shadows from light sources. 注意，GI 效果不能被阴影捕捉器考虑到关于阴影，因为它只与来自光源的阴影工作
• The Shadow Catcher cannot exclude itself from self-shadowing. To do so, the 阴影捕捉器不能排除自我阴影。为了达到这个目的，我们需要Self Shadowing 自我阴影 option must be disabled in the 选项必须在Compositing 合成 tag. 标签
• The Shadow Catcher does not work with the Physical Renderer if soft shadows (shadow maps) are used. 如果使用软阴影(阴影地图) ，阴影捕捉器不能与物理渲染器一起工作