利用Projector实现伪动态阴影

C#

浏览数:170

2019-8-30

传统的阴影实现方法是基于ShadowMap的原理,ShadowMap是以光源为视角,先渲染一张深度图缓存起来,记录下物体在光源空间的深度,然后在实际的渲染过程中,将接受阴影的物体的转换到光源空间之后的深度与深度图作比较,如果比深度图要深,则该点处于阴影之中。

Unity自带的阴影在某些手机上存在硬件不支持的情况,另一种实现阴影的方式可以通过Projector+RenderTexture来实现。我们通过在projector上挂载阴影相机,将相机渲染到RenderTexture上,再将RenderTexture作为贴图传递给Projector的材质,即可实现动态阴影。

projector上挂载的脚本如下:

[RequireComponent(typeof(Projector))]
public class ShadowCameraGenerator : MonoBehaviour 
{
    public LayerMask shadowCasterLayer;
    private RenderTexture _renderTex;

    void Awake()
    {
        Projector projector = GetComponent<Projector>();
        Camera camera = gameObject.AddComponent<Camera>();
        camera.cullingMask = shadowCasterLayer;
        camera.orthographic = true;
        camera.orthographicSize = projector.orthographicSize;
        camera.clearFlags = CameraClearFlags.SolidColor;
        camera.backgroundColor = new Color(1.0f,1.0f,1.0f,0.0f);
        _renderTex = new RenderTexture(1024,1024,0,RenderTextureFormat.ARGB32);
        camera.targetTexture = _renderTex;
        camera.SetReplacementShader(Shader.Find("Unlit/ReplaceShadowRender"),null);
        projector.material.SetTexture("_ShadowTex",_renderTex);
    }

    //ignore black quad occur when editor stop play
    #if UNITY_EDITOR
    void OnApplicationQuit()
    {   
        Projector projector = GetComponent<Projector>();
        projector.material.SetTexture("_ShadowTex",null);
    }
    #endif
}

使用Projector来实现阴影时,需要注意的几点:

  1. 传递给Projector材质的RenderTexture必须是clamp模式,但是如果阴影到了RenderTexture边缘的像素,因为是Clamp的原因,地板就会出现整个长条形的阴影,解决方案可以通过给projector材质添加mask图来处理边缘的像素。
  2. 使用阴影相机时,设置replaceshader,因为只需要物体的alpha信息,因此阴影相机渲染时使用最简单的shader即可。
  3. RenderTexture的大小会决定阴影的质量,图越小,阴影质量越差。

Projector Shader

Shader "Projector/Multiply" {
    Properties {
        _ShadowTex ("Cookie", 2D) = "black"{}
        _FalloffTex ("FallOff", 2D) = "white" {}
    }
    Subshader {
        Tags {"Queue"="Transparent"}
        Pass {
            ZWrite Off
            ColorMask RGB
            Blend DstColor Zero
            Offset -1, -1

            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_fog
            #include "UnityCG.cginc"
            
            struct v2f {
                float4 uvShadow : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 pos : SV_POSITION;
            };
            
            float4x4 unity_Projector;

            v2f vert (float4 vertex : POSITION)
            {
                v2f o;
                o.pos = mul (UNITY_MATRIX_MVP, vertex);
                o.uvShadow = mul (unity_Projector, vertex);
                UNITY_TRANSFER_FOG(o,o.pos);
                return o;
            }
            
            sampler2D _ShadowTex;
            sampler2D _FalloffTex;
            
            fixed4 frag (v2f i) : SV_Target
            {
                fixed4 texS = tex2Dproj (_ShadowTex, UNITY_PROJ_COORD(i.uvShadow));
                fixed4 texF = tex2Dproj (_FalloffTex, UNITY_PROJ_COORD(i.uvShadow));
                fixed ratio =  texF.r * texS.a;
                fixed4 res = fixed4(1,1,1,1) *  (1 - ratio);
                UNITY_APPLY_FOG_COLOR(i.fogCoord, res, fixed4(1,1,1,1));
                return res;
            }
            ENDCG
        }
    }
}

作者:叶小榕