GPU Instancing + Texture2DArray

create-texture2d-array.cs

// https://www.reddit.com/r/Unity3D/comments/6uueox/gpu_instancing_texture2darray/

Texture2D[] textures;
int textureWidth = 256
int textureHeight = 256

Texture2DArray textureArray = new Texture2DArray(textureWidth, textureHeight, textures.Length, TextureFormat.RGBA32, false);

for (int i = 0; i < textures.Length; i++)
{
    Graphics.CopyTexture(textures[i], 0, 0, textureArray, i, 0); // i is the index of the texture
}

material.SetTexture("_Textures", textureArray);

Texture2DArraySurface.Shader

Shader "Custom/Texture2DArraySurfaceShader"
{
    Properties
    {
        _Textures("Textures", 2DArray) = "" {}
    }

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

        CGPROGRAM

        #pragma surface surf Standard fullforwardshadows
        #pragma target 3.5
        #include "UnityCG.cginc"

        UNITY_DECLARE_TEX2DARRAY(_Textures);

        struct Input
        {
            fixed2 uv_Textures;
        };

        UNITY_INSTANCING_CBUFFER_START(Props)
            UNITY_DEFINE_INSTANCED_PROP(float4, _Color)
            UNITY_DEFINE_INSTANCED_PROP(float, _TextureIndex)
        UNITY_INSTANCING_CBUFFER_END

        void surf (Input IN, inout SurfaceOutputStandard o)
        {
            fixed4 c = UNITY_SAMPLE_TEX2DARRAY(_Textures, float3(IN.uv_Textures, UNITY_ACCESS_INSTANCED_PROP(_TextureIndex)) * UNITY_ACCESS_INSTANCED_PROP(_Color);
            o.Albedo = c.rgb;
            o.Alpha = c.a;
        }

        ENDCG
    }
    FallBack "Diffuse"
}