Replacing shaders at runtime

In the Built-in Render PipelineA series of operations that take the contents of a Scene, and displays them on a screen. Unity lets you choose from pre-built render pipelines, or write your own. More info
See in Glossary, you can tell a CameraA component which creates an image of a particular viewpoint in your scene. The output is either drawn to the screen or captured as a texture. More info
See in Glossary to change the shader that it uses to render certain geometry at runtime. You might do this to achieve a visual effect such as edge detection.

Shader replacement is done from scriptsA piece of code that allows you to create your own Components, trigger game events, modify Component properties over time and respond to user input in any way you like. More info
See in Glossary with either the Camera.RenderWithShader or Camera.SetReplacementShader function. Both functions take a shaderA program that runs on the GPU. More info
See in Glossary and a replacementTag.

It works like this: the camera renders the sceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
See in Glossary as it normally would. The objects still use their materials, but the shader they use changes:

• If replacementTag is empty (must be an empty string not null), then all objects in the scene are rendered with the given replacement shader.
• If replacementTag is not empty, then for each object that would be rendered:
  • The real object’s shader is queried for the tag value.
  • If it does not have that tag, object is not rendered.
  • A subshader is found in the replacement shader that has a given tag with the found value. If no such subshader is found, object is not rendered.
  • Now that subshader is used to render the object.

So if all shaders would have, for example, a “RenderType” tag with values like “Opaque”, “Transparent”, “Background”, “Overlay”, you could write a replacement shader that only renders solid objects by using one subshader with RenderType=Solid tagA reference word which you can assign to one or more GameObjects to help you identify GameObjects for scripting purposes. For example, you might define and “Edible” Tag for any item the player can eat in your game. More info
See in Glossary. The other tag types would not be found in the replacement shader, so the objects would be not rendered. Or you could write several subshaders for different “RenderType” tag values. Incidentally, all built-in Shader objectsAn instance of the Shader class, a Shader object is container for shader programs and GPU instructions, and information that tells Unity how to use them. Use them with materials to determine the appearance of your scene. More info
See in Glossary have a “RenderType” tag set.

Lit shader replacement

When using shader replacement the scene is rendered using the render path that is configured on the camera. This means that the shader used for replacement can contain shadow and lighting passes (you can use surface shaders for shader replacement). This can be useful for doing rendering of special effects and scene debugging.

Shader replacement tags in built-in shaders

All built-in shaders have a “RenderType” tag set that can be used when rendering with replaced shaders. Tag values are the following:

• Opaque: most of the shaders (NormalThe direction perpendicular to the surface of a mesh, represented by a Vector. Unity uses normals to determine object orientation and apply shading. More info
  See in Glossary, Self Illuminated, Reflective, terrain shaders).
• Transparent: most semitransparent shaders (Transparent, Particle, Font, terrain additive pass shaders).
• TransparentCutout: masked transparency shaders (Transparent Cutout, two pass vegetation shaders).
• Background: SkyboxA special type of Material used to represent skies. Usually six-sided. More info
  See in Glossary shaders.
• Overlay: Halo, Flare shaders.
• TreeOpaque: terrainThe landscape in your scene. A Terrain GameObject adds a large flat plane to your scene and you can use the Terrain’s Inspector window to create a detailed landscape. More info
  See in Glossary engine tree bark.
• TreeTransparentCutout: terrain engine tree leaves.
• TreeBillboard: terrain engine billboarded trees.
• Grass: terrain engine grass.
• GrassBillboard: terrain engine billboarded grass.

Built-in scene depth/normals texture

A Camera has a built-in capability to render depth or depth+normals texture, if you need that in some of your effects. See Camera Depth Texture page. Note that in some cases (depending on the hardware), the depth and depth+normals textures can internally be rendered using shader replacement. So it is important to have the correct “RenderType” tag in your shaders.

Code Example

Your Start() function specifies the replacement shaders:

void Start() {
    camera.SetReplacementShader (EffectShader, "RenderType");
}

This requests that the EffectShader will use the RenderType key. The EffectShader will have key-value tags for each RenderType that you want. The Shader will look something like:

Shader "EffectShader" {
     SubShader {
         Tags { "RenderType"="Opaque" }
         Pass {
             ...
         }
     }
     SubShader {
         Tags { "RenderType"="SomethingElse" }
         Pass {
             ...
         }
     }
 ...
 }

SetReplacementShader will look through all the objects in the scene and, instead of using their normal shader, use the first subshader which has a matching value for the specified key. In this example, any objects whose shader has Rendertype=“Opaque” tag will be replaced by first subshader in EffectShader, any objects with RenderType=“SomethingElse” shader will use second replacement subshader and so one. Any objects whose shader does not have a matching tag value for the specified key in the replacement shader will not be rendered.