using UnityEngine;
using System.Collections;

// This is in fact just the Water script from Pro Standard Assets,
// just with refraction stuff removed.

[ExecuteInEditMode] // Make mirror live-update even when not in play mode
public class MirrorReflection : MonoBehaviour
{
    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
    
    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!
	// これはカメラに反映したいオブジェクトがあったときに実行する。
	public void OnWillRenderObject()
    {
        if( !enabled || !GetComponent<Renderer>() || !GetComponent<Renderer>().sharedMaterial || !GetComponent<Renderer>().enabled || !SystemInfo.supportsRenderTextures )
            return;
            
        Camera cam = Camera.current;
        if( !cam )
            return;

		// Safeguard from recursive reflections.
		// 再帰的な反射から守りなさい　→　反射出来たら実行しない
		if ( s_InsideRendering )
            return;
        s_InsideRendering = true;
        
        Camera reflectionCamera;
        CreateMirrorObjects( cam, out reflectionCamera );

		// find out the reflection plane: position and normal in world space
		// 反射平面を見つけ出しなさい：ワールド座標の位置と標準
		Vector3 pos = transform.position;
        Vector3 normal = transform.up;

		// Optionally disable pixel lights for reflection
		// オプションで、反射のためのピクセル照明を使用不可にしなさい
		int oldPixelLightCount = QualitySettings.pixelLightCount;
        if( m_DisablePixelLights )
            QualitySettings.pixelLightCount = 0;
        
        UpdateCameraModes( cam, reflectionCamera );

		// Render reflection
		// Reflect camera around reflection plane
		// 反射をしなさい
		// 反射平面のまわりでカメラを反映してください
		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.
		// 平面に近いセットアップ斜め投影法マトリックスは、反射平面です。このように、我々は下 / それより上のすべてを自由に切り取る。
		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 = new Vector3(0, euler.y, euler.z);
        reflectionCamera.Render();
        reflectionCamera.transform.position = oldpos;
        GL.SetRevertBackfacing (false);
        Material[] materials = GetComponent<Renderer>().sharedMaterials;
        foreach( Material mat in materials ) {
            if( mat.HasProperty("_ReflectionTex") )
                mat.SetTexture( "_ReflectionTex", m_ReflectionTexture );
        }

		// Set matrix on the shader that transforms UVs from object space into screen space. We want to just project reflection texture on screen.
		// UVを物体空間からスクリーン座標に変える遮光物の上に、マトリックスを置いてください。ここで反射テクスチャーをスクリーンに映したいです。
        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
		// ピクセル照明数を元に戻してください
		if ( m_DisablePixelLights )
            QualitySettings.pixelLightCount = oldPixelLightCount;
        
        s_InsideRendering = false;
    }


	// Cleanup all the objects we possibly have created
	// 作成されたすべてのオブジェクトを初期化
	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 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_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.
    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;
    }
}