Unity Real-time Reflection Effect Optimization

1. The Result and Cost of the Effect after Optimization

Here is the basic background: There are 8 people on the same screen with the highest picture quality, and it takes 1.1ms (Qualcomm Snapdragon 710). Because the project is not released yet, only test figures can be used for related explanations.

2. The Original Source Code

• Source code

using UnityEngine;
using System.Collections;

[ExecuteInEditMode]
public class MirrorReflection : MonoBehaviour
{
    public Material m_matCopyDepth;
    public bool m_DisablePixelLights = true;
    public int m_TextureSize = 256;
    public float m_ClipPlaneOffset = 0.07f;

    public LayerMask m_ReflectLayers = -1;

    private Hashtable m_ReflectionCameras = new Hashtable(); // Camera -> Camera table

    public RenderTexture m_ReflectionTexture = null;
    public RenderTexture m_ReflectionDepthTexture = null;
    private int m_OldReflectionTextureSize = 0;

    private static bool s_InsideRendering = false;

    public void OnWillRenderObject()
    {
        if (!enabled || !GetComponent<Renderer>() || !GetComponent<Renderer>().sharedMaterial || !GetComponent<Renderer>().enabled)
            return;

        Camera cam = Camera.current;
        if (!cam)
            return;

        // Safeguard from recursive reflections.
        if (s_InsideRendering)
            return;
        s_InsideRendering = true;

        Camera reflectionCamera;
        CreateMirrorObjects(cam, out reflectionCamera);

        // find out the reflection plane: position and normal in world space
        Vector3 pos = transform.position;
        Vector3 normal = transform.up;

        // 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_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;

        // 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);
        GL.invertCulling = true;
        reflectionCamera.transform.position = newpos;
        Vector3 euler = cam.transform.eulerAngles;
        reflectionCamera.transform.eulerAngles = new Vector3(0, euler.y, euler.z);
        reflectionCamera.depthTextureMode = DepthTextureMode.Depth;
        reflectionCamera.Render();

        // copy depth
        Graphics.SetRenderTarget(m_ReflectionDepthTexture);
        m_matCopyDepth.SetPass(0);
        DrawFullscreenQuad();
        Graphics.SetRenderTarget(null);
        // Graphics.Blit(m_ReflectionTexture, m_ReflectionDepthTexture, m_matCopyDepth);

        reflectionCamera.transform.position = oldpos;
        //GL.SetRevertBackfacing(false);
        GL.invertCulling = false;
        Material[] materials = GetComponent<Renderer>().sharedMaterials;
        foreach (Material mat in materials)
        {
            mat.SetTexture("_ReflectionTex", m_ReflectionTexture);
            mat.SetTexture("_ReflectionDepthTex", m_ReflectionDepthTexture);
        }

        // // 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.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;
        }
        if (m_ReflectionDepthTexture)
        {
            DestroyImmediate(m_ReflectionDepthTexture);
            m_ReflectionDepthTexture = 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 CreateMirrorObjects(Camera currentCamera, out Camera reflectionCamera)
    {
        reflectionCamera = null;

        // Reflection render texture
        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_ReflectionTexture.filterMode = FilterMode.Bilinear;

            if (m_ReflectionDepthTexture)
                DestroyImmediate(m_ReflectionDepthTexture);
            m_ReflectionDepthTexture = new RenderTexture(m_TextureSize, m_TextureSize, 0, RenderTextureFormat.RHalf);
            // m_ReflectionDepthTexture = new RenderTexture(m_TextureSize, m_TextureSize, 0, RenderTextureFormat.R8);
            m_ReflectionDepthTexture.name = "__MirrorReflectionDepth" + GetInstanceID();
            m_ReflectionDepthTexture.isPowerOfTwo = true;
            m_ReflectionDepthTexture.hideFlags = HideFlags.DontSave;
            m_ReflectionDepthTexture.filterMode = FilterMode.Bilinear;

            m_OldReflectionTextureSize = m_TextureSize;
        }

        // 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("Mirror Refl Camera id" + GetInstanceID() + " for " + currentCamera.GetInstanceID(), typeof(Camera), typeof(Skybox));
            reflectionCamera = go.GetComponent<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_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));
    }

    // 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;
    }

    static public void DrawFullscreenQuad(float z = 1.0f)
    {
        GL.Begin(GL.QUADS);
        GL.Vertex3(-1.0f, -1.0f, z);
        GL.Vertex3(1.0f, -1.0f, z);
        GL.Vertex3(1.0f, 1.0f, z);
        GL.Vertex3(-1.0f, 1.0f, z);

        GL.Vertex3(-1.0f, 1.0f, z);
        GL.Vertex3(1.0f, 1.0f, z);
        GL.Vertex3(1.0f, -1.0f, z);
        GL.Vertex3(-1.0f, -1.0f, z);
        GL.End();
    }
}

Related Contents: https://github.com/unity3d-jp/unitychan-crs/blob/master/Assets/UnityChanStage/Visualizer/MirrorReflection.cs

Click to see what are the problems with this effect code and how to optimize them: https://blog.en.uwa4d.com/2022/11/09/unity-real-time-reflection-related-optimization/