Creating shaders that support GPU instancing

This page contains information on how to add GPU instancing support to a custom Unity shader. It first explains the shader keywords, variables, and functions custom Unity shaders require to support GPU instancing. Then it includes examples of how to add per-instance data to both surface shaders and vertex/fragment shaders.

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Shader modifications

This section contains information about shader additions that relate to GPU instancing.

When you use multiple per-instance properties, you don’t need to fill all of them in MaterialPropertyBlock objects. Also, if one instance lacks a property, Unity takes the default value from the referenced material. If the material doesn’t have a default value for the property, Unity sets the value to 0. Don’t put non-instanced properties in the MaterialPropertyBlock, because this disables instancing. Instead, create different materials for them.

Instancing_options switches

The [#pragma instancing_options](#pragma-instancing_options) directive can use the following switches:

Using shader variants with GPU instancing

Unity generates Surface shaders with instancing variants by default, unless you specify noinstancing in the #pragma directive. Unity ignores uses of #pragma multi_compile_instancing in a surface shader.

Unity’s Standard and StandardSpecular shaders have instancing support by default, but with no per-instance properties other than the transform.

If your scene contains no GameObjects with GPU instancing enabled, then Unity strips instancing shader variants. To override the stripping behaviour:

1. Open Project Settings (menu: Edit > Project Settings).
2. Go to Graphics.
3. In the Shader Stripping section, set Instancing Variants to Keep All.

Adding per-instance properties to GPU instancing shaders

By default, Unity GPU instances GameObjects with different Transforms in each instanced draw call. To add more variation to the instances, modify the shader to add per-instance properties such as color. You can do this both in surface shaders and in vertex/fragment shaders.

Custom shaders don’t need per-instance data, but they do require an instance ID because world matrices need one to function correctly. Surface shaders automatically set up an instance ID, but custom vertex and fragment shaders don’t. To set up the ID for custom vertex and fragment shaders, use UNITY_SETUP_INSTANCE_ID at the beginning of the shader. For an example of how to do this, see Vertex and fragment shader.

When you declare an instanced property, Unity gathers all the property values from the MaterialPropertyBlock objects set on GameObjects into a single draw call. For an example of how to use MaterialPropertyBlock objects to set per-instance data at runtime, see Changing per-instance data at runtime.

When adding per-instance data to multi-pass shaders, keep the following in mind:

• If a multi-pass shader has more than two passes, Unity only instances the first pass. This is because Unity renders later passes together for each object, which forces material changes.
• If you use the Forward rendering path in the Built-in Render Pipeline, Unity can’t efficiently instance objects that are affected by multiple lights. Unity can only use instancing effectively for the base pass, not for additional passes. For more information about lighting passes, see documentation on Forward Rendering and Pass Tags.

Surface shader example

The following example demonstrates how to create an instanced Surface Shader with different color values for each instance.

Shader "Custom/InstancedColorSurfaceShader"
{
    Properties
    {
        _Color ("Color", Color) = (1,1,1,1)
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
        _Glossiness ("Smoothness", Range(0,1)) = 0.5
        _Metallic ("Metallic", Range(0,1)) = 0.0
    }

    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 200
        CGPROGRAM
        // Uses the physically based standard lighting model with shadows enabled for all light types.
        #pragma surface surf Standard fullforwardshadows
        // Use Shader model 3.0 target
        #pragma target 3.0
        sampler2D _MainTex;
        struct Input
        {
            float2 uv_MainTex;
        };
        half _Glossiness;
        half _Metallic;
        UNITY_INSTANCING_BUFFER_START(Props)
           UNITY_DEFINE_INSTANCED_PROP(fixed4, _Color)
        UNITY_INSTANCING_BUFFER_END(Props)
        void surf (Input IN, inout SurfaceOutputStandard o) {
            fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * UNITY_ACCESS_INSTANCED_PROP(Props, _Color);
            o.Albedo = c.rgb;
            o.Metallic = _Metallic;
            o.Smoothness = _Glossiness;
            o.Alpha = c.a;
        }
        ENDCG
    }
    FallBack "Diffuse"
}

Vertex and fragment shader example

The following example demonstrates how to create an instanced vertex and fragment shader with different color values for each instance. Unlike the surface shader, when you create the vertex and fragment shader you must use UNITY_SETUP_INSTANCE_ID to manually set up an instance ID.

Shader "Custom/SimplestInstancedShader"
{
    Properties
    {
        _Color ("Color", Color) = (1, 1, 1, 1)
    }

    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_instancing
            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct v2f
            {
                float4 vertex : SV_POSITION;
                UNITY_VERTEX_INPUT_INSTANCE_ID // use this to access instanced properties in the fragment shader.
            };

            UNITY_INSTANCING_BUFFER_START(Props)
                UNITY_DEFINE_INSTANCED_PROP(float4, _Color)
            UNITY_INSTANCING_BUFFER_END(Props)

            v2f vert(appdata v)
            {
                v2f o;

                UNITY_SETUP_INSTANCE_ID(v);
                UNITY_TRANSFER_INSTANCE_ID(v, o);
                o.vertex = UnityObjectToClipPos(v.vertex);
                return o;
            }

            fixed4 frag(v2f i) : SV_Target
            {
                UNITY_SETUP_INSTANCE_ID(i);
                return UNITY_ACCESS_INSTANCED_PROP(Props, _Color);
            }
            ENDCG
        }
    }
}

Changing per-instance data at runtime example

The following example demonstrates how to use MaterialPropertyBlock objects to set per-instance data for a group of GameObjects at runtime. It sets the _Color property from the above shader examples to a random color.

Important: MaterialPropertyBlocks break SRP Batcher compatibility. For more information, see GPU instancing: Requirements and Compatibility.

using UnityEngine;

public class MaterialPropertyBlockExample : MonoBehaviour
{
    public GameObject[] objects;

    void Start()
    {
        MaterialPropertyBlock props = new MaterialPropertyBlock();
        MeshRenderer renderer;

        foreach (GameObject obj in objects)
        {
            float r = Random.Range(0.0f, 1.0f);
            float g = Random.Range(0.0f, 1.0f);
            float b = Random.Range(0.0f, 1.0f);
            props.SetColor("_Color", new Color(r, g, b));

            renderer = obj.GetComponent<MeshRenderer>();
            renderer.SetPropertyBlock(props);
        }
    }
}