unity planar实时阴影

废话不多先上图片 实时阴影效果 带渐变的

接着上代码

Shader "Custom/NewShader" {
    Properties {
        _MainTex ("Base (RGB)", 2D) = "white" {}
        //*********************绘制阴影的参数****************************
        _ShadowPlane ("Shadow Plane", Vector) = (0,1,0,0.02)
        _ShadowColor("Shadow Color",Color) = (0.2, 0.2, 0.2, 1)
        _ShadowPara("Shadow Param",Vector) = (-0.006,60,3,0.02)
        _lightDirection("LightDir",Vector) = (0,-1,0)
        //*************************************************
    }
    SubShader {
        Tags { "RenderType"="Opaque" }
        LOD 200

        CGPROGRAM
        #pragma surface surf Lambert

        sampler2D _MainTex;

        struct Input {
            float2 uv_MainTex;
        };

        void surf (Input IN, inout SurfaceOutput o) {
            half4 c = tex2D (_MainTex, IN.uv_MainTex);
            o.Albedo = c.rgb;
            o.Alpha = c.a;
        }
        ENDCG
        //*******************绘制阴影的参数pass 只需要在你原来的shader里面加入这个pass就可以绘制出实时阴影了******************************
        pass{
            Tags { "QUEUE"="Transparent" "RenderType"="Transparent" }
            ZWrite Off
            Fog { Mode Off }
            Blend SrcAlpha OneMinusSrcAlpha
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"
            struct v2f { 
                float4 pos : SV_POSITION;
                half3 texcord0 : TEXCOORD0;
                half3 texcord1 : TEXCOORD1;
            };
            uniform fixed4 _ShadowPlane;
            uniform fixed4 _ShadowPara;
            uniform fixed3 _lightDirection;
            uniform fixed4 _ShadowColor;
            v2f vert(appdata_tan v)
            {
                  v2f o;
                  fixed3 vt;
                  vt = mul(_Object2World , v.vertex).xyz;
                  fixed3 tmpvar_3;
                  tmpvar_3 = (vt - (( (dot (_ShadowPlane.xyz, vt) - _ShadowPlane.w) / dot (_ShadowPlane.xyz, _lightDirection)) * _lightDirection));
                  fixed4 tmpvar_4;
                  tmpvar_4.w = 1.0;
                  tmpvar_4.xyz = tmpvar_3;
                  o.pos = mul(UNITY_MATRIX_VP , tmpvar_4);
                  o.texcord0 = mul(_Object2World,float4(0, 0, 0, 1));
                  o.texcord1 = tmpvar_3;
                  return o;
            }

            float4 frag(v2f inData) : COLOR
            {
                fixed3 posToPlane = inData.texcord0-inData.texcord1;
                fixed4 f = _ShadowColor;
                fixed v = pow (1.0 - clamp ((( sqrt( dot(posToPlane,posToPlane) ) * _ShadowPara.w) - _ShadowPara.x),0,1),_ShadowPara.y) * _ShadowPara.z;
                f.w = v * _ShadowColor.a;
                return f;
            }
            ENDCG
        }
        //*************************************************

    } 
    FallBack "Diffuse"
}

plannar实时阴影最基本的原理如下：

 

float4 vPosWorld = mul( _Object2World, v.vertex);
float4 lightDirection = -normalize(_WorldSpaceLightPos0); 
float opposite = vPosWorld.y - _PlaneHeight;
float cosTheta = -lightDirection.y;	// = lightDirection dot (0,-1,0)
float hypotenuse = opposite / cosTheta;
float3 vPos = vPosWorld.xyz + ( lightDirection * hypotenuse );
o.pos = mul (UNITY_MATRIX_VP, float4(vPos.x, _PlaneHeight, vPos.z ,1));  

详细见：https://github.com/ozlael/PlannarShadowForUnity