Unity GPU Instancing

.gpu-instancing.md

https://docs.unity3d.com/Manual/GPUInstancing.html

GPU Instancing (Unity)

Introduction

Use GPU Instancing to draw (or render) multiple copies of the same Mesh at once, using a small number of draw calls. It is useful for drawing objects such as buildings, trees and grass, or other things that appear repeatedly in a Scene .

GPU Instancing only renders identical Meshes with each draw call, but each instance can have different parameters (for example, color or scale) to add variation and reduce the appearance of repetition.

GPU Instancing can reduce the number of draw calls used per Scene. This significantly improves the rendering performance of your project.

Adding per-instance data

By default, Unity only batches instances of GameObjects with different Transforms in each instanced draw call. To add more variance to your instanced GameObjects, modify your Shader to add per-instance properties such as Material color.

The example below demonstrates how to create an instanced Shader with different colour values for each instance.

gpu-instancing-material-property-block.cs

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);
}

gpu-instancing-shader-simple.glsl

Shader "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 // necessary only if you want to access instanced properties in __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); // necessary only if you want to access instanced properties in the fragment Shader.

                o.vertex = UnityObjectToClipPos(v.vertex);
                return o;
            }
           
            fixed4 frag(v2f i) : SV_Target
            {
                UNITY_SETUP_INSTANCE_ID(i); // necessary only if any instanced properties are going to be accessed in the fragment Shader.
                return UNITY_ACCESS_INSTANCED_PROP(Props, _Color);
            }
            ENDCG
        }
    }
}

gpu-instancing-shader.glsl

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
        // Physically based Standard lighting model, and enable shadows on 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"
}