Output a motion vector texture in a custom shader in URP

For URP to render the MotionVectors pass for a ShaderLabUnity’s language for defining the structure of Shader objects. More info
See in Glossary shaderA program that runs on the GPU. More info
See in Glossary, make sure that its active SubShader contains a pass with the following LightMode tag:

Tags { "LightMode" = "MotionVectors" }

For example:

Shader “Example/MyCustomShaderWithPerObjectMotionVectors"
{
    SubShader
    {
        // ...other passes, SubShader tags and commands
    
        Pass
        {
            Tags { "LightMode" = "MotionVectors" }
            ColorMask RG
            
            HLSLPROGRAM
            
            // Your shader code goes here.
            
            ENDHLSL
        }
    }
}

For an example of adding motion vector pass support for features such as alpha clipping, LODThe Level Of Detail (LOD) technique is an optimization that reduces the number of triangles that Unity has to render for a GameObject when its distance from the Camera increases. More info
See in Glossary cross-fade, or alembic animation, refer to the implementation of the MotionVectors pass in URP pre-built ShaderLab shaders, for example, the Unlit.shader file. The rendering of your MotionVectors pass should match your non-motion-vector passes and should reflect any custom deformation and/or vertex animation a pass is performing.

If a custom shader is only intended for objects with transform motion or skinned animation, without using alpha clipping, LOD cross-fade, alembic animation, custom deformation, or vertex animation, the motion vector fallback shader provided by URP might be enough. To add the pre-built fallback shader, add the following ShaderLab command to your SubShader blocks:

Shader “Example/MyCustomShaderWithPerObjectMotionVectorFallback"
{
    SubShader
    {
        // ...other passes, SubShader tags, and commands
    
        UsePass "Hidden/Universal Render Pipeline/ObjectMotionVectorFallback/MOTIONVECTORS"
    }
}

Note: In Unity versions earlier than 2023.2, URP would automatically use the fallback pass for all SubShader blocks which don’t have a pass tagged with the MotionVectors LightMode tag. Starting from Unity 2023.2, this fallback logic is disabled for the following reasons:

• The fallback logic was only an initial implementation detail meant for URP’s own Materials.
• URP Materials now use material-type-specific motion vector passes to support features like alpha clip, LOD cross-fade, or alembic animation, making the fallback obsolete.
• The fallback logic was causing unintended visual artifacts for content which it was not applicable to (for example, decals which should not draw any object motion vectors).