[Port] [2022.3] DOCG-7473 Move channel packing to its own task page, clarify steps

Author: markg-unity

Packages/com.unity.render-pipelines.universal/Documentation~/TableOfContents.md

@@ -109,6 +109,7 @@
       * [Fullscreen Master Stack in Shader Graph reference for URP](urp-shaders/fullscreen-master-stack-reference.md)
 * [Shaders and Materials](shaders-in-universalrp.md)
   * [Shading Models](shading-model.md)
+  * [Assign a channel-packed texture to a material](shaders-in-universalrp-channel-packed-texture.md)
   * [Material Variants](materialvariant-URP.md)
   * [Complex Lit](shader-complex-lit.md)
   * [Lit](lit-shader.md)

Packages/com.unity.render-pipelines.universal/Documentation~/lit-shader.md

@@ -47,6 +47,8 @@ The __Surface Options__ control how URP renders the Material on a screen.
 
 The __Surface Inputs__ describe the surface itself. For example, you can use these properties to make your surface look wet, dry, rough, or smooth.
 
+You can use a single RGBA texture for the metallic, smoothness, and occlusion properties. For more information, refer to [Assign a channel-packed texture to a material in URP](shaders-in-universalrp-channel-packed-texture.md).
+
 **Note:** If you are used to the [Standard Shader](https://docs.unity3d.com/Manual/Shader-StandardShader.html) in the built-in Unity render pipeline, these options are similar to the Main Maps settings in the [Material Editor](https://docs.unity3d.com/Manual/StandardShaderContextAndContent.html).
 
 

Packages/com.unity.render-pipelines.universal/Documentation~/shader-complex-lit.md

@@ -49,6 +49,8 @@ The __Surface Options__ control how URP renders the Material on a screen.
 
 The __Surface Inputs__ describe the surface itself. For example, you can use these properties to make your surface look wet, dry, rough, or smooth.
 
+You can use a single RGBA texture for the metallic, smoothness, and occlusion properties. For more information, refer to [Assign a channel-packed texture to a material in URP](shaders-in-universalrp-channel-packed-texture.md).
+
 **Note:** If you are used to the [Standard Shader](https://docs.unity3d.com/Manual/Shader-StandardShader.html) in the built-in Unity render pipeline, these options are similar to the Main Maps settings in the [Material Editor](https://docs.unity3d.com/Manual/StandardShaderContextAndContent.html).
 
 

Packages/com.unity.render-pipelines.universal/Documentation~/shaders-in-universalrp-channel-packed-texture.md

@@ -0,0 +1,27 @@
+# Assign a channel-packed texture to a URP material
+
+In the [Lit](lit-shader) and [Complex Lit](shader-complex-lit) shaders in the Universal Render Pipeline (URP), you can use a single RGBA texture for the metallic, smoothness, and occlusion properties. This technique is called channel packing or texture packing.
+
+Follow these steps:
+
+1. Create a texture with the following channels:
+
+    | **Channel** | **Property** |
+    | - | - |
+    | Red   | Metallic |
+    | Green | Occlusion |
+    | Blue  | Not used |
+    | Alpha | Smoothness |
+
+2. [Import the texture](https://docs.unity3d.com/Manual/ImportingTextures).
+
+3. In the Inspector window for the texture, disable **sRGB (Color Texture)**.
+
+4. Assign the texture to the **Metallic** and **Occlusion** properties of the material. Unity automatically uses the correct channels from the texture.
+
+You can use [Shader Graph](https://docs.unity3d.com/Manual/shader-graph) instead if you pack channels in textures differently.
+
+## Additional resources
+
+- [Materials](https://docs.unity3d.com/Manual/Materials)
+- [Custom textures](https://docs.unity3d.com/Manual/Textures-landing)