Ok guys, tricky one!I'm trying to modify this Unity script + shader to include normal mapping. The tl;dr is, it uses a single texture rather than a cubemap as it is only for reflecting in a planar surface. So it doesn't use the standard ray bounce onto an axis aligned cube. Instead it :creates a reflection matrix from the plane (pos and normal)reflects the camera position and view matrix through the planerenders to texture from the reflected camera (with oblique near clipping plane set to cull everything behind the mirror)creates a projection matrix and sends it as uniform to the shader (basically just a standard MVP matrix but with scale cancelled, and biased from [-1, 1] to [0, 1]multiplies the object space coordinate by the projection matrix to get a texcoord and then looks up the mirror texture with thisSo there are no normals actually used in the shader at all at present. I know how to construct a TBN matrix and use this to warp the per-pixel normals, but I have no idea how this translates into a texture offset in this case. I have a feeling I might need screen-space normals like in the question here but pretty stumped beyond that. Any ideas?EDIT -- Here's the scriptusing UnityEngine;using System.Collections;[ExecuteInEditMode()]public class PlanarRealtimeReflection : MonoBehaviour{    public bool m_DisablePixelLights = true;    public int m_TextureResolution = 1024;    public float m_clipPlaneOffset = 0.07f;    private float m_finalClipPlaneOffset = 0.0f;    public bool m_NormalsFromMesh = false;    public bool m_BaseClipOffsetFromMesh = false;    public bool m_BaseClipOffsetFromMeshInverted = false;    private Vector3 m_calculatedNormal = Vector3.zero;    private Vector3 m_calculatedTangent = Vector4.zero;    public LayerMask m_ReflectLayers = -1;    private Hashtable m_ReflectionCameras = new Hashtable(); //Camera -> Camera table    private RenderTexture m_ReflectionTexture = null;    private int m_OldReflectionTextureSize = 0;    private static bool s_InsideRendering = false;    //This is called when it's known that the object will be rendered by some    //camera. We render reflections and do other updates here.    //Because the script executes in edit mode, reflections for the scene view    //camera will just work!    public void OnWillRenderObject()    {        if(!enabled || !renderer || !renderer.sharedMaterial || !renderer.enabled)            return;        Camera cam = Camera.current;        if(!cam)            return;        if(m_NormalsFromMesh && GetComponent<MeshFilter>() != null)            m_calculatedNormal = transform.TransformDirection(GetComponent<MeshFilter>().sharedMesh.normals[0]);            m_calculatedTangent = transform.TransformDirection(GetComponent<MeshFilter>().sharedMesh.tangents[0]);        if(m_BaseClipOffsetFromMesh && GetComponent<MeshFilter>() != null)            m_finalClipPlaneOffset = (transform.position - transform.TransformPoint(GetComponent<MeshFilter>().sharedMesh.vertices[0])).magnitude + m_clipPlaneOffset;        else if(m_BaseClipOffsetFromMeshInverted && GetComponent<MeshFilter>() != null)            m_finalClipPlaneOffset = -(transform.position - transform.TransformPoint(GetComponent<MeshFilter>().sharedMesh.vertices[0])).magnitude + m_clipPlaneOffset;        else            m_finalClipPlaneOffset = m_clipPlaneOffset;        //Safeguard from recursive reflections.                if(s_InsideRendering)            return;        s_InsideRendering = true;        Camera reflectionCamera;        CreateSurfaceObjects(cam, out reflectionCamera);        //Find out the reflection plane: position and normal in world space        Vector3 pos = transform.position;        Vector3 normal = m_NormalsFromMesh && GetComponent<MeshFilter>() != null ? m_calculatedNormal : transform.up;        Vector3 tangent = m_NormalsFromMesh && GetComponent<MeshFilter>() != null ? m_calculatedTangent : transform.right;        Vector3 bitangent = Vector3.Cross(normal, tangent);        //Optionally disable pixel lights for reflection        int oldPixelLightCount = QualitySettings.pixelLightCount;        if(m_DisablePixelLights)            QualitySettings.pixelLightCount = 0;        UpdateCameraModes(cam, reflectionCamera);        //Render reflection        //Reflect camera around reflection plane        float d = -Vector3.Dot (normal, pos) - m_finalClipPlaneOffset;        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;        //Setup oblique projection matrix so that near plane is our reflection plane.        //This way we clip everything below/above it for free.        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; //never render water layer        reflectionCamera.targetTexture = m_ReflectionTexture;        GL.SetRevertBackfacing (true);        reflectionCamera.transform.position = newpos;        //Vector3 euler = cam.transform.eulerAngles;        //reflectionCamera.transform.eulerAngles = euler; // 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(_ReflectionTex))                  mat.SetTexture(_ReflectionTex, m_ReflectionTexture);            mat.SetVector(_Normal, new Vector4(normal.x,normal.y,normal.z,0));            mat.SetVector(_Tangent, new Vector4(tangent.x, tangent.y, tangent.z));            mat.SetVector(_Bitangent, new Vector4(bitangent.x, bitangent.y, bitangent.z));        }        //Set matrix on the shader that transforms UVs from object space into screen        //space. We want to just project reflection texture on screen.        Matrix4x4 scaleOffset = Matrix4x4.TRS(            new Vector3(0.5f,0.5f,0.5f), Quaternion.identity, new Vector3(0.5f,0.5f,0.5f));        Vector3 scale = transform.localScale;//.lossyScale;        Matrix4x4 mtx = transform.localToWorldMatrix * Matrix4x4.Scale(new Vector3(1.0f/scale.x, 1.0f/scale.y, 1.0f/scale.z));        mtx = scaleOffset *  cam.projectionMatrix * cam.worldToCameraMatrix * mtx;        foreach(Material mat in materials)            mat.SetMatrix(_ProjMatrix, mtx);        //Restore pixel light count        if(m_DisablePixelLights)            QualitySettings.pixelLightCount = oldPixelLightCount;        s_InsideRendering = false;    }    //Cleanup all the objects we possibly have created    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;        //set camera to clear the same way as current camera        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;            }        }        //update other values to match current camera.        //even if we are supplying custom camera&projection matrices,        //some of values are used elsewhere (e.g. skybox uses far plane)        dest.farClipPlane = src.farClipPlane;        dest.nearClipPlane = src.nearClipPlane;        dest.orthographic = src.orthographic;        dest.fieldOfView = src.fieldOfView;        dest.aspect = src.aspect;        dest.orthographicSize = src.orthographicSize;    }    //On-demand create any objects we need    private void CreateSurfaceObjects(Camera currentCamera, out Camera reflectionCamera)    {        reflectionCamera = null;        //Reflection render texture        if(!m_ReflectionTexture || m_OldReflectionTextureSize != m_TextureResolution)        {            if(m_ReflectionTexture)                DestroyImmediate(m_ReflectionTexture);            m_ReflectionTexture = new RenderTexture(m_TextureResolution, m_TextureResolution, 16);            m_ReflectionTexture.name = __SurfaceReflection + GetInstanceID();            m_ReflectionTexture.isPowerOfTwo = true;            m_ReflectionTexture.hideFlags = HideFlags.DontSave;            m_OldReflectionTextureSize = m_TextureResolution;        }        //Camera for reflection        reflectionCamera = m_ReflectionCameras[currentCamera] as Camera;        if(!reflectionCamera) //catch both not-in-dictionary and in-dictionary-but-deleted-GO        {            GameObject go = new GameObject(Surface 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;        }            }    //Extended sign: returns -1, 0 or 1 based on sign of a    private static float sgn(float a)    {        if (a > 0.0f) return 1.0f;        if (a < 0.0f) return -1.0f;        return 0.0f;    }    //Given position/normal of the plane, calculates plane in camera space.    private Vector4 CameraSpacePlane (Camera cam, Vector3 pos, Vector3 normal, float sideSign)    {        Vector3 offsetPos = pos + normal * m_finalClipPlaneOffset;        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));    }    //Adjusts the given projection matrix so that near plane is the given clipPlane    //clipPlane is given in camera space. See article in Game Programming Gems 5 and    //http://aras-p.info/texts/obliqueortho.html    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)));        //third row = clip plane - fourth row        projection[2] = c.x - projection[3];        projection[6] = c.y - projection[7];        projection[10] = c.z - projection[11];        projection[14] = c.w - projection[15];    }    //Calculates reflection matrix around the given plane    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;    }}And the shader so farShader Realtime Reflections/New Shader{    Properties {                _MainAlpha(MainAlpha, Range(0, 1)) = 1        _MapAmount(Distortion Amount, Range(0, 0.05)) = 0        _MainTex (Base (RGB) Gloss (A), 2D) = white {}        _ReflectionTex (Reflection, 2D) = white {}        _NormalMap (Normal Map, 2D) = white {}        _RefColor(Color,Color) = (1,1,1,1)    }    SubShader {        Tags {            RenderType=Opaque}        LOD 100        Pass {            CGPROGRAM            #pragma vertex vert            #pragma fragment frag            #include UnityCG.cginc            uniform float4x4    _ProjMatrix;            uniform float       _RefType;            uniform float4      _Normal;            uniform float4      _Tangent;            uniform float4      _Bitangent;            sampler2D           _ReflectionTex;            sampler2D           _MainTex;            sampler2D           _NormalMap;            float4              _MainTex_ST;            float4              _NormalMap_ST;                   float4              _RefColor;            float               _MainAlpha;            float               _MapAmount;            struct outvertex {                float4 pos :        SV_POSITION;                float2 colorUV :    TEXCOORD0;                float2 bumpUV :     TEXCOORD1;                float4 varyingPos : TEXCOORD2;            };            outvertex vert(appdata_full v) {                outvertex o;                o.pos = mul (UNITY_MATRIX_MVP,v.vertex);                o.colorUV = TRANSFORM_TEX(v.texcoord.xy,_MainTex);                o.bumpUV = TRANSFORM_TEX(v.texcoord1.xy,_NormalMap);                o.varyingPos = v.vertex;                    o. color = fixed4(mul(float3x3(UNITY_MATRIX_IT_MV),v.normal),1);                return o;            }            float4 frag(outvertex i) : COLOR {                          float4 posProj = mul(_ProjMatrix, i.varyingPos);                      float2 normPosProj = posProj.xy / posProj.w;                float3 bump = (float3(tex2D(_NormalMap, i.bumpUV));                //normPosProj += ?????????                half4 flecol = tex2D(_ReflectionTex, normPosProj);                  half4 maincol =  tex2D(_MainTex, i.colorUV);                                                    half4 outcolor = half4(1,1,1,1);                                outcolor = maincol*_MainAlpha+flecol*(1-_MainAlpha);                return outcolor*_RefColor;            }            ENDCG        }    }}I had the idea to get the normal in screen space (so z is always toward camera) then simply find the delta between the regular normal and the warped one in x,y and use this as the texture offset, but I have no idea if this is feasible or how to do it.
Normal mapping for planar reflections
reflection