shader实例水(反射，法线，透明)

unity自带的资源中有水的例子，导入步骤为：Assets-Import Package-Water (Pro Only)，熟悉相关参数就可以调出很漂亮的水效果，但是作为程序员不能只停留在使用层，了解其中的原理才是我们追寻的目标。

先看看效果，这样学习兴趣会更大。

因为unity自带demo集成的比较多，作为新手很难进行学习，所以就在网上先找关于反射的资料，不找不知道一找吓一跳，反射才不简单！不过现在不用看懂它会用就好，在这里反射被封装为一个名为Mirror的cs脚本，将这个脚本绑定到水的对象上就可以获取当前反射的贴图，然后将贴图传到shader中就可以显示。之前有接触过grabpass，法线贴图，所以现在只需要加上反射就能实现一个普通水的效果，显然通过设置参数这个shader还可以用于镜面反射，玻璃效果等等。而在这之前完全不懂这些是啥，所以获得经验：有规划的进行学习终究有所收获。

 

原理和shader代码如下(有不对的地方希望能指出)：

Shader "Mirrors/Transparent Bumped Specular Flat" {
 Properties {
  _Speed ("UV移动速度", Range (-1,1)) = 0
  _Transparency("材质透明度", Range (0, 1)) = 1
  _Distortion ("针对法线贴图的扭曲程度", range (0,0.4)) = 0

  _Color ("主色", Color) = (1,1,1,1)
  _MainTex ("主材质", 2D) = "white" {}
  _BlendLevel("主材质显示强度",Range(0,1))=1
  _SpecColor ("镜面颜色", Color) = (0.5, 0.5, 0.5, 1)
  _Shininess ("镜面强度", Range (0.01, 1)) = 0.078125

  _BumpMap ("法线贴图", 2D) = "bump" {}
  _Bumpness ("法线颜色强度",Range(0,1))= 1
  _Ref ("来自镜面反射", 2D) = "white" {}
 }

 SubShader {
  Tags { "Queue"="Transparent" "RenderType"="Opaque" }
  GrabPass {       
   Name "BASE"
   Tags { "LightMode" = "Always" }
   }

  CGPROGRAM
  #pragma surface surf BlinnPhong
  #pragma target 3.0

  half _Speed; // uv移动速度
  half _Transparency;//材质透明度
  half _Distortion;// 扭曲强度
  fixed4 _Color; //主色
  sampler2D _MainTex;// 主材质图
  half _BlendLevel;// 主材质强度
  half _Shininess;// 镜面强度
  sampler2D _BumpMap;// 法线贴图
  half _Bumpness;// 法线颜色强度
  sampler2D _Ref; // 反射贴图
  sampler2D _GrabTexture;// 屏幕纹理

  struct Input {
   float2 uv_MainTex; // 主贴图
   float2 uv_BumpMap; // 法线贴图
   float4 screenPos; // 顶点在屏幕坐标的位置
  };

  void surf (Input IN, inout SurfaceOutput o) {
   // 移动法线纹理的X
   IN.uv_BumpMap.x = IN.uv_BumpMap.x + _Speed * _Time;
   // 对法线贴图进行采样
   fixed3 nor = UnpackNormal (tex2D(_BumpMap, IN.uv_BumpMap));
   // 对主材质进行采样
   fixed4 tex = tex2D(_MainTex, IN.uv_MainTex);

   // 【将反射的图像正常显示在此对象上】
   // 获取屏幕纹理坐标信息
   float2 screenUV = IN.screenPos.xy / IN.screenPos.w;
   // 针对法线纹理做法线扭曲，_Distortion为扭曲强度
   screenUV += nor.xy * _Distortion ; 
   // 对反射纹理进行采样，通过屏幕纹理
   fixed4 ref = tex2D(_Ref, screenUV);
 
   // 【将屏幕的纹理正常显示在此对象上】，如果不需要半透明可去掉
   // 获取顶点在屏幕的坐标为纹理
   float4 screenUV2 = IN.screenPos;
   // 以下是根据平台来判断是否需要倒置Y坐标
   // D3D:scale=-1，那么screenUV2.y = -1 * screenUV2.y + screenUV2.w;【倒置后+w让值域保持为0到1】
   // OpenGL:scale=1，那么screenUV2.y = screenUV2.y;
   #if UNITY_UV_STARTS_AT_TOP
   float scale = -1.0;
   #else
   float scale = 1.0;
   #endif
   screenUV2.y = (screenUV2.y - screenUV2.w * 0.5) * scale + screenUV2.w * 0.5;
   screenUV2.xy = screenUV2.xy / screenUV2.w;
   // 针对法线纹理做的法线扭曲,_Distortion为强度
   screenUV2.xy += nor.xy * _Distortion;
   // 对屏幕纹理进行采样
   fixed4 trans = tex2D(_GrabTexture,screenUV2.xy);
  
   // 最终颜色 = 主材质颜色 * 主颜色 * 主色显示强度
   o.Albedo = tex.rgb * _Color.rgb * _BlendLevel;
   // 反射颜色 = 反射材质颜色和【屏幕纹理颜色】的插值
   o.Emission = lerp(ref.rgb,trans.rgb,_Transparency);
   // 法线值 = 法线材质颜色 * 法线强度
   o.Normal = nor.rgb * _Bumpness;
   // 发光强度 = 主纹理A
   o.Gloss = tex.a;
   // 透明度 = 主色
   o.Alpha = tex.a * _Color.a;
   // 镜面高光【高光需要针对针对非立方体，如果是平面BlinnPhong也无效】
   o.Specular = _Shininess * _SpecColor; 
  }
  ENDCG
 }//end subshader
}

 

镜子代码Mirror 如下：

using UnityEngine;

using System.Collections;

[ExecuteInEditMode]
public class Mirror : MonoBehaviour
{
    public bool m_DisablePixelLights = true;
    public int m_TextureSize = 256;
    public float m_ClipPlaneOffset = 0.07f;
 public bool m_IsFlatMirror = true;
  
    public LayerMask m_ReflectLayers = -1;
      
    private Hashtable m_ReflectionCameras = new Hashtable();
  
    private RenderTexture m_ReflectionTexture = null;
    private int m_OldReflectionTextureSize = 0;
  
    private static bool s_InsideRendering = false;

    public void OnWillRenderObject()
    {
        if( !enabled || !renderer || !renderer.sharedMaterial || !renderer.enabled )
            return;
          
        Camera cam = Camera.current;
        if( !cam )
            return;
  
        if( s_InsideRendering )
            return;
        s_InsideRendering = true;
      
        Camera reflectionCamera;
        CreateMirrorObjects( cam, out reflectionCamera );
      
        Vector3 pos = transform.position;
  Vector3 normal;
  if(m_IsFlatMirror){
         normal = transform.up;
  }
  else{
   normal= transform.position - cam.transform.position ;
   normal.Normalize();
  }
        int oldPixelLightCount = QualitySettings.pixelLightCount;
        if( m_DisablePixelLights )
            QualitySettings.pixelLightCount = 0;
      
        UpdateCameraModes( cam, reflectionCamera );

        float d = -Vector3.Dot (normal, pos) - m_ClipPlaneOffset;
        Vector4 reflectionPlane = new Vector4 (normal.x, normal.y, normal.z, d);
  
        Matrix4x4 reflection = Matrix4x4.zero;
        CalculateReflectionMatrix (ref reflection, reflectionPlane);
        Vector3 oldpos = cam.transform.position;
        Vector3 newpos = reflection.MultiplyPoint( oldpos );
        reflectionCamera.worldToCameraMatrix = cam.worldToCameraMatrix * reflection;
  

        Vector4 clipPlane = CameraSpacePlane( reflectionCamera, pos, normal, 1.0f );
        Matrix4x4 projection = cam.projectionMatrix;
        CalculateObliqueMatrix (ref projection, clipPlane);
        reflectionCamera.projectionMatrix = projection;
      
        reflectionCamera.cullingMask = ~(1<<4) & m_ReflectLayers.value;
        reflectionCamera.targetTexture = m_ReflectionTexture;
        GL.SetRevertBackfacing (true);
        reflectionCamera.transform.position = newpos;
        Vector3 euler = cam.transform.eulerAngles;
        reflectionCamera.transform.eulerAngles = new Vector3(0, euler.y, euler.z);
        reflectionCamera.Render();
        reflectionCamera.transform.position = oldpos;
        GL.SetRevertBackfacing (false);
        Material[] materials = renderer.sharedMaterials;
        foreach( Material mat in materials ) {
            if( mat.HasProperty("_Ref") )
                mat.SetTexture( "_Ref", m_ReflectionTexture );
        }
        if( m_DisablePixelLights )
            QualitySettings.pixelLightCount = oldPixelLightCount;
      
        s_InsideRendering = false;
    }
  
    void OnDisable()
    {
        if( m_ReflectionTexture ) {
            DestroyImmediate( m_ReflectionTexture );
            m_ReflectionTexture = null;
        }
        foreach( DictionaryEntry kvp in m_ReflectionCameras )
            DestroyImmediate( ((Camera)kvp.Value).gameObject );
        m_ReflectionCameras.Clear();
    }
  
  
    private void UpdateCameraModes( Camera src, Camera dest )
    {
        if( dest == null )
            return;

        dest.clearFlags = src.clearFlags;
        dest.backgroundColor = src.backgroundColor;      
        if( src.clearFlags == CameraClearFlags.Skybox )
        {
            Skybox sky = src.GetComponent(typeof(Skybox)) as Skybox;
            Skybox mysky = dest.GetComponent(typeof(Skybox)) as Skybox;
            if( !sky || !sky.material )
            {
                mysky.enabled = false;
            }
            else
            {
                mysky.enabled = true;
                mysky.material = sky.material;
            }
        }

        dest.farClipPlane = src.farClipPlane;
        dest.nearClipPlane = src.nearClipPlane;
        dest.orthographic = src.orthographic;
        dest.fieldOfView = src.fieldOfView;
        dest.aspect = src.aspect;
        dest.orthographicSize = src.orthographicSize;
  dest.renderingPath = src.renderingPath;
    }
  

    private void CreateMirrorObjects( Camera currentCamera, out Camera reflectionCamera )
    {
        reflectionCamera = null;
      

        if( !m_ReflectionTexture || m_OldReflectionTextureSize != m_TextureSize )
        {
            if( m_ReflectionTexture )
                DestroyImmediate( m_ReflectionTexture );
            m_ReflectionTexture = new RenderTexture( m_TextureSize, m_TextureSize, 16 );
            m_ReflectionTexture.name = "__MirrorReflection" + GetInstanceID();
            m_ReflectionTexture.isPowerOfTwo = true;
            m_ReflectionTexture.hideFlags = HideFlags.DontSave;
            m_OldReflectionTextureSize = m_TextureSize;
        }
      

        reflectionCamera = m_ReflectionCameras[currentCamera] as Camera;
        if( !reflectionCamera )
        {
            GameObject go = new GameObject( "Mirror Refl Camera id" + GetInstanceID() + " for " + currentCamera.GetInstanceID(), typeof(Camera), typeof(Skybox) );
            reflectionCamera = go.camera;
            reflectionCamera.enabled = false;
            reflectionCamera.transform.position = transform.position;
            reflectionCamera.transform.rotation = transform.rotation;
            reflectionCamera.gameObject.AddComponent("FlareLayer");
            go.hideFlags = HideFlags.HideAndDontSave;
            m_ReflectionCameras[currentCamera] = reflectionCamera;
        }      
    }
  
    private static float sgn(float a)
    {
        if (a > 0.0f) return 1.0f;
        if (a < 0.0f) return -1.0f;
        return 0.0f;
    }
  
    private Vector4 CameraSpacePlane (Camera cam, Vector3 pos, Vector3 normal, float sideSign)
    {
        Vector3 offsetPos = pos + normal * m_ClipPlaneOffset;
        Matrix4x4 m = cam.worldToCameraMatrix;
        Vector3 cpos = m.MultiplyPoint( offsetPos );
        Vector3 cnormal = m.MultiplyVector( normal ).normalized * sideSign;
        return new Vector4( cnormal.x, cnormal.y, cnormal.z, -Vector3.Dot(cpos,cnormal) );
    }
  
    private static void CalculateObliqueMatrix (ref Matrix4x4 projection, Vector4 clipPlane)
    {
        Vector4 q = projection.inverse * new Vector4(
            sgn(clipPlane.x),
            sgn(clipPlane.y),
            1.0f,
            1.0f
        );
        Vector4 c = clipPlane * (2.0F / (Vector4.Dot (clipPlane, q)));

        projection[2] = c.x - projection[3];
        projection[6] = c.y - projection[7];
        projection[10] = c.z - projection[11];
        projection[14] = c.w - projection[15];
    }

    private static void CalculateReflectionMatrix (ref Matrix4x4 reflectionMat, Vector4 plane)
    {
        reflectionMat.m00 = (1F - 2F*plane[0]*plane[0]);
        reflectionMat.m01 = (   - 2F*plane[0]*plane[1]);
        reflectionMat.m02 = (   - 2F*plane[0]*plane[2]);
        reflectionMat.m03 = (   - 2F*plane[3]*plane[0]);

        reflectionMat.m10 = (   - 2F*plane[1]*plane[0]);
        reflectionMat.m11 = (1F - 2F*plane[1]*plane[1]);
        reflectionMat.m12 = (   - 2F*plane[1]*plane[2]);
        reflectionMat.m13 = (   - 2F*plane[3]*plane[1]);
  
        reflectionMat.m20 = (   - 2F*plane[2]*plane[0]);
        reflectionMat.m21 = (   - 2F*plane[2]*plane[1]);
        reflectionMat.m22 = (1F - 2F*plane[2]*plane[2]);
        reflectionMat.m23 = (   - 2F*plane[3]*plane[2]);

        reflectionMat.m30 = 0F;
        reflectionMat.m31 = 0F;
        reflectionMat.m32 = 0F;
        reflectionMat.m33 = 1F;
    }
}