Unity Shader Example 29 (平面阴影)

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

public class Player : MonoBehaviour
{
    public static Player Instance = null;

    public Camera mCamera;

    public CharacterController mCharCtrl;

    public Light mLight;

    private Animation mAnim;

    private List<Material> mMatList = new List<Material>();

    #region 内置函数

    private void Awake()
    {
        Instance = this;

        SkinnedMeshRenderer[] renderlist = GetComponentsInChildren<SkinnedMeshRenderer>();
        foreach(var render in renderlist)
        {
            if (render == null)
                continue;

            mMatList.Add(render.material);
        }
    }

    // Use this for initialization
    void Start () 
    {
        mAnim = GetComponentInChildren<Animation>();
    }

    // Update is called once per frame
    void Update ()
    {
        //UpdatePos();
        UpdateShader();
    }

    #endregion

    #region 函数



    private void UpdateShader()
    {
        Vector4 worldpos = transform.position;

        //Vector4 projdir = new Vector4(-0.06323785f, -0.9545552f, -0.2912483f, 1.0f);
        //mLight.transform.rotation = Quaternion.LookRotation(projdir);

        Vector4 projdir = mLight.transform.forward;

        foreach (var mat in mMatList)
        {
            if (mat == null)
                continue;

            mat.SetVector("_WorldPos", worldpos);
            mat.SetVector("_ShadowProjDir", projdir);
            mat.SetVector("_ShadowPlane", new Vector4(0.0f, 1.0f, 0.0f, 0.1f));
            mat.SetVector("_ShadowFadeParams", new Vector4(0.0f, 1.5f, 0.7f, 0.0f));
            mat.SetFloat("_ShadowFalloff", 1.35f);
        }
    }

    #endregion
}

这个cs脚本主要是给shader的变量进行赋值。

Shader "PlanarShadow/Shadow"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
		_ShadowInvLen ("ShadowInvLen", float) = 1.0 //0.4449261
	
	}
	
	SubShader
	{
		Tags{ "RenderType" = "Opaque" "Queue" = "Geometry+10" }
		LOD 100
		
		Pass
		{
			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;

			v2f vert (appdata v)
			{
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				o.uv = TRANSFORM_TEX(v.uv, _MainTex);
				UNITY_TRANSFER_FOG(o,o.vertex);
				return o;
			}
			
			fixed4 frag (v2f i) : SV_Target
			{
				// sample the texture
				fixed4 col = tex2D(_MainTex, i.uv);
				// apply fog
				UNITY_APPLY_FOG(i.fogCoord, col);
				return col;
			}
			
			ENDCG
		}

		Pass
		{		
			Blend SrcAlpha  OneMinusSrcAlpha
			ZWrite Off
			Cull Back
			ColorMask RGB

			Stencil
			{
				Ref 1			
				Comp NotEqual			
				WriteMask 255		
				ReadMask 255
				Pass Replace
				Fail Keep
				ZFail Keep

			}


			CGPROGRAM
			
			#pragma vertex vert
			#pragma fragment frag

			float4 _ShadowPlane;
			float4 _ShadowProjDir;
			float4 _WorldPos;
			float _ShadowInvLen;
			float4 _ShadowFadeParams;
			float _ShadowFalloff;
			
			struct appdata
			{
				float4 vertex : POSITION;
			};

			struct v2f
			{
				float4 vertex : SV_POSITION;
				float3 xlv_TEXCOORD0 : TEXCOORD0;
			};

			v2f vert(appdata v)
			{
				v2f o;

				float3 lightdir = normalize(_ShadowProjDir);
				float3 worldpos = mul(unity_ObjectToWorld, v.vertex).xyz;
				// _ShadowPlane.w = p0 * n  // 平面的w分量就是p0 * n
				float distance = (_ShadowPlane.w - dot(_ShadowPlane.xyz, worldpos)) / dot(_ShadowPlane.xyz, lightdir.xyz);
				float3 shadowWorldpos = worldpos + distance * lightdir.xyz;

				o.vertex = mul(unity_MatrixVP, float4(shadowWorldpos, 1.0));
				o.xlv_TEXCOORD0 = shadowWorldpos;

				return o;
			}
			
			float4 frag(v2f i) : SV_Target
			{
				float3 posToPlane_2 = (_WorldPos.xyz - i.xlv_TEXCOORD0);
				float4 color;
				color.rgb = float3(0.0, 0.0, 0.0);
				
				// 下面两种阴影衰减公式都可以使用(当然也可以自己写衰减公式)
				// 王者荣耀的衰减公式
				//color.a = (pow((1.0 - clamp(((sqrt(dot(posToPlane_2, posToPlane_2)) * _ShadowInvLen) - _ShadowFadeParams.x), 0.0, 1.0)), _ShadowFadeParams.y) * _ShadowFadeParams.z);

				// 另外的阴影衰减公式
				color.a = 1.0 - saturate(distance(_WorldPos.xyz, i.xlv_TEXCOORD0) * _ShadowFalloff);

				return color;
			}
			
			ENDCG
		}
	}
}

细节

a.

float distance = (_ShadowPlane.w - dot(_ShadowPlane.xyz, worldpos)) / dot(_ShadowPlane.xyz, lightdir.xyz);
float3 shadowWorldpos = worldpos + distance * lightdir.xyz;

作用：

计算物体投影到 plane 上的 顶点的坐标，也就是阴影坐标。

具体的算法涉及到：Line–plane intersection（https://en.wikipedia.org/wiki/Line%E2%80%93plane_intersection ）

b.

                // 下面两种阴影衰减公式都可以使用(当然也可以自己写衰减公式)
				// 王者荣耀的衰减公式
				//color.a = (pow((1.0 - clamp(((sqrt(dot(posToPlane_2, posToPlane_2)) * _ShadowInvLen) - _ShadowFadeParams.x), 0.0, 1.0)), _ShadowFadeParams.y) * _ShadowFadeParams.z);

				// 另外的阴影衰减公式
				color.a = 1.0 - saturate(distance(_WorldPos.xyz, i.xlv_TEXCOORD0) * _ShadowFalloff);

作用：

所谓的衰减其实就是计算alpha值，衰减公式可以看效果来调。

c.

            Stencil
			{
				Ref 1			
				Comp NotEqual			
				WriteMask 255		
				ReadMask 255
				Pass Replace
				Fail Keep
				ZFail Keep

			}

作用：

设置模板，主要的作用就是同一个模型下，投影到平面上 重复的点 不进行渲染。