全局雾效

通过屏幕后处理实现雾效可以不用修改场景物体的 shader，方便自由控制
还是参照《unity shader入门精要》

// 引入雾效相关的参数
_FogStart ("FogStart", float) = 1
_FogEnd ("FogEnd", float) = 1
_FogColor ("FogColor", Color) = (1,1,1,1)
_FogDesity ("FogDesity", float) = 1

// 根据场景高度计算雾的浓度，和场景颜色做差值
float4 color =  tex2D(_MainTex, i.uv);
float fogDensity = (_FogEnd - worldPos.y) / (_FogEnd - _FogStart);
fogDensity = saturate(fogDensity * _FogDesity);
color.rgb = lerp(color.rgb, _FogColor.rgb, fogDensity);
return color;

雾的最终效果

高度雾

扫描线

// in fragment shader
float linear01Depth = Linear01Depth(depthTextureValue);
float d = distance(worldPos, _ScanCenter);

// 在场景中，并在扫描区域
if (linear01Depth < 1 && _ScanRange - d > 0)
{
        // 根据坐标到中心的距离计算扫描线，加入扫描线宽度的控制
    float r = saturate(1 - (_ScanRange - d) / _ScanWidth);
    return _LineColor * r + color;
}

// 不在扫描区域显示默认画面
return color;

// in c#
private Vector3 mouseWorldPos;
private float scanWidth = 0f;
public float scanSpeed = 0f;

...

void Update()
{
        // 鼠标点击位置为扫描区域中心
    if (Input.GetMouseButtonDown(0))
    {
        Ray ray = currentCamera.ScreenPointToRay(Input.mousePosition);
        RaycastHit hit;
        if (Physics.Raycast(ray, out hit))
        {
            mouseWorldPos.x = hit.point.x;
            mouseWorldPos.z = hit.point.y;
            mouseWorldPos = hit.point;
            scanWidth = 0;
        }
    }
        
        // 范围随着时间扩大
    scanWidth += Time.deltaTime * scanSpeed;
}

...

postEffectMaterial.SetVector("_ScanCenter", mouseWorldPos);
postEffectMaterial.SetFloat("_ScanRange", scanWidth);

最终效果

扫描线

进一步：加入墙体和墙体后被遮挡的物体
利用 Stencil 可以区分绘制物体被遮挡的部分
先绘制墙后的物体，并写入Stencil
然后绘制墙，不覆盖绘制墙体后的物体

// object behind wall
Shader "Unlit/ObjectBehindWall"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _Color ("Color", Color) = (1,1,1,1)
        _Outline ("Outline", float) = 1
        _Fresnel ("Fresnel", float) = 1
    }

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

            Stencil {
                Ref 1
                Comp Always
                pass Replace
            }
            
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
                float3 normal : NORMAL;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
                float3 normal : NORMAL;
                float3 worldPos : TEXCOORD1;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            float4 _Color;
            float _Outline;
            float _Fresnel;

            v2f vert (appdata v)
            {
                v2f o;
                float3 normal = UnityObjectToWorldNormal(v.normal);
                o.vertex = UnityObjectToClipPos(v.vertex + normal * _Outline);
                o.worldPos = mul(unity_ObjectToWorld, v.vertex).xyz;
                o.normal = normal;
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                float3 V = normalize(_WorldSpaceCameraPos.xyz - i.worldPos);
                float3 N = normalize(i.normal);
                float NdotV = saturate(dot(V, N));

                float fresnel = pow(1 - NdotV, _Fresnel);
                if (fresnel < 0.2) {
                    discard;
                }

                float4 col = _Color;
                col.rgb *= fresnel;

                return col;
            }
            ENDCG
        }        
    }

    Fallback "Diffuse"
}

// wall
Shader "Unlit/wall"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _Color ("Color", Color) = (1,1,1,1)
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            Stencil {
                Ref 1
                Comp NotEqual
            }

            CGPROGRAM
            #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;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            float4 _Color;

            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
            {
                // sample the texture
                fixed4 col = tex2D(_MainTex, i.uv) * _Color;
                return col;
            }
            ENDCG
        }
    }
}

墙使用的是 unlit 的材质，这样就不会写入深度

墙后的物体使用的也是 unlit 材质。在后面加上 Fallback "Diffuse"，由于引入了阴影，就会写入深度纹理

最后的效果，在物体上绘制扫描线，墙上不绘制扫描线

最终效果