shader实现雪地中的脚印

效果图：点击地面产生坑！！！

总体思路：
1.用一张RT 标记人走过的痕迹
2.将痕迹映射到雪地上
3.雪地上痕迹凹陷混合
4. 凹陷和突起，阴影，法线。。。。。。等（未做）

第一步：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;public class Snow : MonoBehaviour
{public RenderTexture rt;// 为了混合 rt,但不能直接用rt,所以先用rt0接收中转RenderTexture rt0;// 画笔public Texture drawImg;// 清屏显示public Texture defaultImg;public Camera mainCam;// 用于混合rt和 画 的材质public Material drawMat;void Start(){mainCam = Camera.main.GetComponent<Camera>();GetComponent<Renderer>().material.mainTexture = rt;DrawDefault();rt0 = new RenderTexture(rt.width, rt.height, 32, rt.graphicsFormat);rt0.Create();}private void DrawDefault(){RenderTexture.active = rt;GL.PushMatrix();GL.LoadPixelMatrix(0, rt.width,  rt.height, 0);Rect rect = new Rect(0, 0, rt.width, rt.height);Graphics.DrawTexture(rect, defaultImg);GL.PopMatrix();RenderTexture.active = null;}private void Draw(int x,int y){Graphics.Blit(rt, rt0);RenderTexture.active = rt;GL.PushMatrix();// 屏幕空间的表现GL.LoadPixelMatrix(0, rt.width, rt.height, 0);// 绘制到中心点x -= (int)(drawImg.width * 0.5f);y -= (int)(drawImg.height * 0.5f);Rect rect = new Rect(x, y, drawImg.width, drawImg.height);Vector4 SourceUV = new Vector4();SourceUV.x = rect.x / rt.width;SourceUV.y = 1 - rect.y / rt.height;SourceUV.z = rect.width / rt.width;SourceUV.w = rect.height / rt.width;SourceUV.y -= SourceUV.w;drawMat.SetTexture("_SourceTex", rt0);drawMat.SetVector("_SourceUV", SourceUV);// 此处如果不用drawMat混合，产生的痕迹会被覆盖掉//Graphics.DrawTexture(rect, drawImg);Graphics.DrawTexture(rect, drawImg,drawMat);GL.PopMatrix();RenderTexture.active = null;}// Update is called once per framevoid Update(){if (Input.GetMouseButton(0)){Debug.LogError("按下");Ray ray = mainCam.ScreenPointToRay(Input.mousePosition);RaycastHit hit;//多加一个参数 限制射线检测的 距离//Physics.Raycast(ray, out hit,0.01f)if (Physics.Raycast(ray,out hit)){                int x = (int)(hit.textureCoord.x * rt.width);// （0，0）点在左上角， 变换到左下角  只变动yint y = (int)(rt.height -hit.textureCoord.y * rt.height);Debug.LogError("点击到" + hit.transform.name + " x="+ x+" y="+y);Draw(x, y);}}}
}

第二步：地面的shader,点击地面后，地面shader的顶点偏移，产生“凹陷”的效果
注意理解tex2Dlod函数的意义

Shader "Unlit/snow"
{Properties{_MainTex ("Texture", 2D) = "white" {}}SubShader{Tags { "RenderType"="Opaque" }LOD 100Pass{CGPROGRAM#pragma vertex vert#pragma fragment frag// make fog work#pragma multi_compile_fog#include "UnityCG.cginc"struct appdata{float4 vertex : POSITION;float2 uv : TEXCOORD0;float3 normal : NORMAL;};struct v2f{float2 uv : TEXCOORD0;UNITY_FOG_COORDS(1)float4 vertex : SV_POSITION;};sampler2D _MainTex;float4 _MainTex_ST;v2f vert (appdata v){v2f o;o.uv = TRANSFORM_TEX(v.uv, _MainTex);// 此函数在 顶点着色器，片元着色器中  都能使用， v.vertex.xyz += tex2Dlod(_MainTex,float4(o.uv,0,0)).r * v.normal;o.vertex = UnityObjectToClipPos(v.vertex);               return o;}fixed4 frag (v2f i) : SV_Target{// sample the texturefixed4 col = tex2D(_MainTex, i.uv);return col;}ENDCG}}
}

第三步：能产生凹凸的效果，但是由于顶点数量有限，所以凹凸效果太突兀（可以用曲面细分来优化）。。。
画笔出的痕迹被自己覆盖，所以混合一下，保证是纯色

Shader "Unlit/draw"
{Properties{_MainTex ("Texture", 2D) = "white" {}_SourceTex("SourceTex", 2D) = "white" {}_SourceUV("SourceUV",Vector) = (0,0,0,0)}SubShader{Tags { "RenderType"="Transparent" }LOD 100Pass{ZWrite OffBlend SrcAlpha OneMinusSrcAlphaCGPROGRAM#pragma vertex vert#pragma fragment frag#include "UnityCG.cginc"struct appdata{float4 vertex : POSITION;float2 uv : TEXCOORD0;};struct v2f{float2 uv : TEXCOORD0;float4 vertex : SV_POSITION;float2 sourceUV : TEXCOORD1;};sampler2D _MainTex;float4 _MainTex_ST;sampler2D _SourceTex;float4 _SourceTex_ST;Vector _SourceUV;v2f vert (appdata v){v2f o;o.vertex = UnityObjectToClipPos(v.vertex);o.uv = TRANSFORM_TEX(v.uv, _MainTex);o.sourceUV = TRANSFORM_TEX(_SourceUV, _SourceTex);return o;}fixed4 frag (v2f i) : SV_Target{                fixed4 col = tex2D(_MainTex, i.uv);fixed4 sCol = tex2D(_SourceTex, i.sourceUV);fixed4 endCol = min(col, sCol);return endCol;}ENDCG}}
}

以上只是宏观上能实现效果，是这么个意思，（美术功底不好不会作图的请脑补一下==），阉割的不能再阉割了。。。。。。迫于没有图片资源，就不上传效果动图了。
参考：
雪地脚印1

-------------------------分割线--------------------------------------------------------

升级版：

使用曲面细分效果：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Experimental.Rendering;public class DrawWithMind : MonoBehaviour
{[SerializeField]public RenderTexture rt;private Camera mainCam;public Material drawMat;Material snowMat;[Range(0, 100)]public float _BrushStrength;[Range(0, 1000)]public float _BrushSize;void Start(){mainCam = Camera.main.GetComponent<Camera>();snowMat = GetComponent<MeshRenderer>().material;rt = new RenderTexture(1024, 1024, 0, GraphicsFormat.R32G32B32A32_SFloat);snowMat.SetTexture("_MaskTex", rt);}Vector4 vec = new Vector4();// Update is called once per framevoid Update(){if (Input.GetMouseButton(0)){Ray ray = mainCam.ScreenPointToRay(Input.mousePosition);if (Physics.Raycast(ray, out var hit)){vec.x = hit.textureCoord.x;vec.y = hit.textureCoord.y;Debug.LogError("hit name =" + hit.transform.name + " pos = " + hit.textureCoord.x + " , " + hit.textureCoord.y + " u=" + vec.x + " v=" + vec.y);drawMat.SetVector("_HitUV", vec);//drawMat.SetFloat("_Strength", _BrushStrength);//drawMat.SetFloat("_powSize", _BrushSize);RenderTexture temp = RenderTexture.GetTemporary(rt.width, rt.height, 0, rt.format);Graphics.Blit(rt, temp);Graphics.Blit(temp, rt, drawMat);RenderTexture.ReleaseTemporary(temp);}}}
}

Shader "Unlit/DrawLine"
{Properties{_MainTex ("Texture", 2D) = "white" {}_Color("LineColor",Color) = (0,1,0,1)[hideIninspector]_HitUV("HitUV",vector) = (0,0,0,0)_powSize("pow size",Range(0,1000)) = 500_Strength("Strength",Range(0,60)) = 10}SubShader{Tags { "RenderType"="Opaque" }LOD 100Pass{CGPROGRAM#pragma vertex vert#pragma fragment frag// make fog work#pragma multi_compile_fog#include "UnityCG.cginc"struct appdata{float4 vertex : POSITION;float2 uv : TEXCOORD0;};struct v2f{float2 uv : TEXCOORD0;UNITY_FOG_COORDS(1)float4 vertex : SV_POSITION;};sampler2D _MainTex;float4 _MainTex_ST;float4 _Color;float _powSize;float _Strength;
vector _HitUV;v2f vert (appdata v){v2f o;o.vertex = UnityObjectToClipPos(v.vertex);o.uv = TRANSFORM_TEX(v.uv, _MainTex);return o;}fixed4 frag (v2f i) : SV_Target{fixed4 col = tex2D(_MainTex, i.uv);float draw = pow(saturate(1 - distance(i.uv,_HitUV.xy)),500/_powSize);fixed4 drawCol = _Color * (draw * _Strength);//col *= draw;return drawCol+ col;}ENDCG}}
}

Shader "Unlit/SnowShader"
{Properties{_Color("Color", Color) = (1,1,1,1)_BaceTex ("BaceTex", 2D) = "white" {}_SnowColor("SnowColor", Color) = (1,1,1,1)_SnowTex("SnowTex", 2D) = "white" {}_MaskTex("mask tex",2D) = "white"{}_aaaa("TesselationNum",Range(0.1,100)) = 0.145299_Displacement("_Displacement",Range(0.1,100)) = 0.5}SubShader{Tags { "RenderType" = "Opaque" }LOD 100Pass{CGPROGRAM#pragma hull hull#pragma domain domain#pragma vertex tessvert#pragma fragment frag#include "UnityCG.cginc"
#include "Tessellation.cginc"
#pragma multi_compile_fwdbase_fullshadows
#pragma only_renderers d3d9 d3d11 glcore gles
#pragma target 4.6sampler2D _BaceTex,_SnowTex,_MaskTex;float4 _MaskTex_ST ;float _aaaa;float4 _Color, _SnowColor;float _Displacement;struct VertexInput{float4 vertex : POSITION;float2 uv : TEXCOORD0;float3 normal : NORMAL;float4 tangent : TANGENT;};struct VertexOutput{float2 uv : TEXCOORD0;float4 pos : SV_POSITION;float3 normal_dir : TEXCOORD1;float2 uv_bace : TEXCOORD2;float2 uv_snow : TEXCOORD3;};VertexOutput vert(VertexInput v){VertexOutput o = (VertexInput)0;o.uv = v.uv;o.normal_dir = UnityObjectToWorldNormal(v.normal);float4 _MaskTex_var = tex2Dlod(_MaskTex, float4(o.uv, 0, 0));float4 _BaceTex_var = tex2Dlod(_BaceTex, float4(o.uv, 0, 0));v.vertex.xyz -= v.normal * (_BaceTex_var.r - 0.7 + _MaskTex_var.r) * _Displacement;o.pos = UnityObjectToClipPos(v.vertex);return o;}#ifdef UNITY_CAN_COMPILE_TESSELLATIONstruct TessVertex {float4 vertex : INTERNALTESSPOS;float3 normal : NORMAL;float4 tangent : TANGENT;float2 uv : TEXCOORD0;};struct OutputPatchConstant {float edge[3] : SV_TessFactor;float inside : SV_InsideTessFactor;float3 vTangent[4] : TANGENT;float2 vUV[4] : TEXCOORD;float3 vTanUCorner[4] : TANUCORNER;float3 vTanVCorner[4] : TANVCORNER;float3 vCWts :TANWELIGHTS;};//将顶点里的处理 传入到曲面细分中TessVertex tessvert(VertexInput v) {TessVertex o;o.vertex = v.vertex;o.normal = v.normal;o.tangent = v.tangent;o.uv = v.uv;return o;}// 曲面细分的  远近控制（近处细分，远处不细分）float4 Tessellation(TessVertex v, TessVertex v1, TessVertex v2) {float minDist = 1.0;float maxDist = 25.0;return UnityDistanceBasedTess(v.vertex, v1.vertex, v2.vertex, minDist, maxDist, _aaaa);}// 曲面细分的强度控制float Tessellation(TessVertex v){return _aaaa;}// InputPatch<TessVertex, 3> 表示输入的 patch 为3个 TessVertex 数据，对应三角形 patch 的3个顶点OutputPatchConstant hullconst(InputPatch<TessVertex, 3> v) {OutputPatchConstant o = (OutputPatchConstant)0;float4 ts = Tessellation(v[0], v[1], v[2]);// 每个边分成几段  o.edge[0] = ts.x;o.edge[1] = ts.y;o.edge[2] = ts.z;// 意味着在三角形内部加入三个新的顶点，但是这个函数并不会创建任何新的顶点，只是会计算出所有新的顶点的重心坐标。o.inside = ts.w;return o;}[domain("tri")] // 定义特性  输入进hull shader的图元是三角形[partitioning("fractional_odd")]// 决定分割方式[outputtopology("triangle_cw")]//决定图元的朝向[patchconstantfunc("hullconst")]// 补丁常量缓存函数名[outputcontrolpoints(3)]//决定三个控制点TessVertex hull(InputPatch<TessVertex, 3> v, uint id : SV_OutputControlPointID) {return v[id];}[domain("tri")]VertexOutput domain(OutputPatchConstant tessFactors, const OutputPatch<TessVertex, 3> vi, float3 bary : SV_DomainLocation){VertexInput v = (VertexInput)0;v.vertex = vi[0].vertex * bary.x + vi[1].vertex * bary.y + vi[2].vertex * bary.z;v.normal = vi[0].normal * bary.x + vi[1].normal * bary.y + vi[2].normal * bary.z;v.tangent = vi[0].tangent * bary.x + vi[1].tangent * bary.y + vi[2].tangent * bary.z;v.uv = vi[0].uv * bary.x + vi[1].uv * bary.y + vi[2].uv * bary.z;VertexOutput o = vert(v);return o;}
#endiffixed4 frag (VertexOutput i) : SV_Target{               float4 _MaskTex_var = tex2D(_MaskTex, TRANSFORM_TEX(i.uv,_MaskTex));float4 BaceTex_var = tex2D(_BaceTex, i.uv) * _Color;float4 SnowTex_var = tex2D(_SnowTex, i.uv) * _SnowColor;float4 c = lerp(BaceTex_var, SnowTex_var, _MaskTex_var.r);float3 finalColor = c.xyz;return fixed4(finalColor,1);}ENDCG}}
}

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