[Unity] 深度バッファから法線を復元しようとしてうまくいかなかった話 ref: http://qiita.com/edo_m18/items/86029fd6c18a52ad4f3d

file0.txt

Shader "Custom/DepthNormal" {
    SubShader {
        Tags { "RenderType"="Transparent" "Queue"="Transparent+10" }
        LOD 200

        Pass
        {
            CGPROGRAM

            #include "UnityCG.cginc"
            #pragma vertex vert
            #pragma fragment frag
            #pragma target 3.0

            uniform sampler2D  _CameraDepthTexture;
            uniform float4x4 _InverseProjection;

            struct v2f
            {
                float4 pos : SV_POSITION;
                float2 uv : TEXCOORD0;
            };

            v2f vert(appdata_img v)
            {
                v2f o = (v2f)0;
                o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                o.uv = v.texcoord.xy;
                return o;
            }

            float4 frag(v2f i) : SV_Target
            {
                float ep = 0.001;

                float2 xy1 = float2(i.uv.x + ep, i.uv.y + ep);
                float2 xy2 = float2(i.uv.x - ep, i.uv.y + ep);
                float2 xy3 = float2(i.uv.x - ep, i.uv.y - ep);
                float2 xy4 = float2(i.uv.x + ep, i.uv.y - ep);

                float z1 = tex2D(_CameraDepthTexture, xy1);
                float z2 = tex2D(_CameraDepthTexture, xy2);
                float z3 = tex2D(_CameraDepthTexture, xy3);
                float z4 = tex2D(_CameraDepthTexture, xy4);

                float4 pPos1 = float4(xy1 * 2 - 1, z1, 1.0);
                float4 p1 = mul(_InverseProjection, pPos1);
                p1.xyz /= p1.w;

                float4 pPos2 = float4(xy2 * 2 - 1, z2, 1.0);
                float4 p2 = mul(_InverseProjection, pPos2);
                p2.xyz /= p2.w;

                float4 pPos3 = float4(xy3 * 2 - 1, z3, 1.0);
                float4 p3 = mul(_InverseProjection, pPos3);
                p3.xyz /= p3.w;

                float4 pPos4 = float4(xy4 * 2 - 1, z4, 1.0);
                float4 p4 = mul(_InverseProjection, pPos4);
                p4.xyz /= p4.w;

                float3 v1 = normalize(p3.xyz - p1.xyz);
                float3 v2 = normalize(p4.xyz - p2.xyz);

                float3 n = normalize(cross(v1, v2));

                return half4(n, 1);
            }

            ENDCG
        }
    }
    FallBack "Diffuse"
}

file1.txt

float ep = 0.001;

float2 xy1 = float2(i.uv.x + ep, i.uv.y + ep);
float2 xy2 = float2(i.uv.x - ep, i.uv.y + ep);
float2 xy3 = float2(i.uv.x - ep, i.uv.y - ep);
float2 xy4 = float2(i.uv.x + ep, i.uv.y - ep);

float z1 = tex2D(_CameraDepthTexture, xy1);
float z2 = tex2D(_CameraDepthTexture, xy2);
float z3 = tex2D(_CameraDepthTexture, xy3);
float z4 = tex2D(_CameraDepthTexture, xy4);

file2.txt

float4 pPos1 = float4(xy1 * 2 - 1, z1, 1.0);

file3.txt

float4 p1 = mul(_InverseProjection, pPos1);
p1.xyz /= p1.w;

file4.txt

float3 v1 = normalize(p3.xyz - p1.xyz);
float3 v2 = normalize(p4.xyz - p2.xyz);
float3 n = normalize(cross(v1, v2));

file5.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[ExecuteInEditMode]
public class DepthEnabler : MonoBehaviour
{
    public Material _material;

    void Start()
    {
        Camera.main.depthTextureMode |= DepthTextureMode.Depth;
    }

    private void OnRenderImage(RenderTexture source, RenderTexture destination)
    {
        Matrix4x4 mat = Camera.main.projectionMatrix;
        _material.SetMatrix("_InverseProjection", mat.inverse);
        Graphics.Blit(source, destination, _material);
    }
}

file6.cs

Camera.main.depthTextureMode |= DepthTextureMode.Depth;