using System;
using System.Collections.Generic;
using UnityEngine.Rendering;
using UnityEngine.Rendering.PostProcessing;
using UnityEngine.XR;

namespace UnityEngine.Experimental.Rendering.LightweightPipeline
{
    [Serializable]
    public class ShadowSettings
    {
        public bool     enabled;
        public int      shadowAtlasWidth;
        public int      shadowAtlasHeight;

        public float    maxShadowDistance;
        public int      directionalLightCascadeCount;
        public Vector3  directionalLightCascades;
        public float    directionalLightNearPlaneOffset;

        static ShadowSettings defaultShadowSettings = null;

        public static ShadowSettings Default
        {
            get
            {
                if (defaultShadowSettings == null)
                {
                    defaultShadowSettings = new ShadowSettings();
                    defaultShadowSettings.enabled = true;
                    defaultShadowSettings.shadowAtlasHeight = defaultShadowSettings.shadowAtlasWidth = 4096;
                    defaultShadowSettings.directionalLightCascadeCount = 1;
                    defaultShadowSettings.directionalLightCascades = new Vector3(0.05F, 0.2F, 0.3F);
                    defaultShadowSettings.directionalLightCascadeCount = 4;
                    defaultShadowSettings.directionalLightNearPlaneOffset = 5;
                    defaultShadowSettings.maxShadowDistance = 1000.0F;
                }
                return defaultShadowSettings;
            }
        }
    }

    public struct ShadowSliceData
    {
        public Matrix4x4    shadowTransform;
        public int          atlasX;
        public int          atlasY;
        public int          shadowResolution;
    }

    public struct LightData
    {
        public int additionalPixelLightsCount;
        public int vertexLightsCount;
        public int mainLightIndex;
        public bool hasAdditionalLights;
        public bool shadowsRendered;
    }

    public class LightweightPipeline : RenderPipeline
    {
        private readonly LightweightPipelineAsset m_Asset;

        // Max amount of visible lights. This controls the lights constant buffers in shader but not the max shaded lights.
        // Lights are set per-object and the max shaded lights for each object are controlled by the max pixel lights in pipeline asset and kMaxVertexLights.
        private static readonly int kMaxVisibleAdditionalLights = 16;
        private static readonly int kMaxPerObjectLights = 8;

        private Vector4[] m_LightPositions = new Vector4[kMaxVisibleAdditionalLights];
        private Vector4[] m_LightColors = new Vector4[kMaxVisibleAdditionalLights];
        private Vector4[] m_LightAttenuations = new Vector4[kMaxVisibleAdditionalLights];
        private Vector4[] m_LightSpotDirections = new Vector4[kMaxVisibleAdditionalLights];

        private Camera m_CurrCamera = null;

        private ComputeBuffer m_LightIndexListBuffer;

        private static readonly int kMaxCascades = 4;
        private int m_ShadowCasterCascadesCount = kMaxCascades;
        private int m_ShadowMapTexture;
        private int m_CameraColorTexture;
        private int m_CameraDepthTexture;
        private int m_CameraCopyDepthTexture;
        private RenderTargetIdentifier m_ShadowMapRT;
        private RenderTargetIdentifier m_CameraColorRT;
        private RenderTargetIdentifier m_CameraDepthRT;
        private RenderTargetIdentifier m_CameraCopyDepthRT;

        private bool m_IntermediateTextureArray = false;

        private const int kShadowDepthBufferBits = 16;
        private const int kCameraDepthBufferBits = 32;
        private Vector4[] m_DirectionalShadowSplitDistances = new Vector4[kMaxCascades];

        private ShadowSettings m_ShadowSettings = ShadowSettings.Default;
        private ShadowSliceData[] m_ShadowSlices = new ShadowSliceData[kMaxCascades];

        private static readonly ShaderPassName m_LitPassName = new ShaderPassName("LightweightForward");
        private static readonly ShaderPassName m_UnlitPassName = new ShaderPassName("SRPDefaultUnlit");

        private RenderTextureFormat m_ColorFormat;
        private PostProcessRenderContext m_PostProcessRenderContext;
        private PostProcessLayer m_CameraPostProcessLayer;

        private CameraComparer m_CameraComparer = new CameraComparer();
        private LightComparer m_LightCompararer = new LightComparer();

        // Maps from sorted light indices to original unsorted. We need this for shadow rendering
        // and per-object light lists.
        private List<int> m_SortedLightIndexMap = new List<int>();

        private Mesh m_BlitQuad;
        private Material m_BlitMaterial;
        private Material m_CopyDepthMaterial;
        private int m_BlitTexID = Shader.PropertyToID("_BlitTex");

        private CopyTextureSupport m_CopyTextureSupport;

        public LightweightPipeline(LightweightPipelineAsset asset)
        {
            m_Asset = asset;

            BuildShadowSettings();

            PerFrameBuffer._GlossyEnvironmentColor = Shader.PropertyToID("_GlossyEnvironmentColor");
            PerFrameBuffer._AttenuationTexture = Shader.PropertyToID("_AttenuationTexture");

            PerCameraBuffer._MainLightPosition = Shader.PropertyToID("_MainLightPosition");
            PerCameraBuffer._MainLightColor = Shader.PropertyToID("_MainLightColor");
            PerCameraBuffer._MainLightAttenuationParams = Shader.PropertyToID("_MainLightAttenuationParams");
            PerCameraBuffer._MainLightSpotDir = Shader.PropertyToID("_MainLightSpotDir");
            PerCameraBuffer._AdditionalLightCount = Shader.PropertyToID("_AdditionalLightCount");
            PerCameraBuffer._AdditionalLightPosition = Shader.PropertyToID("_AdditionalLightPosition");
            PerCameraBuffer._AdditionalLightColor = Shader.PropertyToID("_AdditionalLightColor");
            PerCameraBuffer._AdditionalLightAttenuationParams = Shader.PropertyToID("_AdditionalLightAttenuationParams");
            PerCameraBuffer._AdditionalLightSpotDir = Shader.PropertyToID("_AdditionalLightSpotDir");

            m_ShadowMapTexture = Shader.PropertyToID("_ShadowMap");
            m_CameraColorTexture = Shader.PropertyToID("_CameraColorTexture");
            m_CameraDepthTexture = Shader.PropertyToID("_CameraDepthTexture");
            m_CameraCopyDepthTexture = Shader.PropertyToID("_CameraCopyDepthTexture");

            m_ShadowMapRT = new RenderTargetIdentifier(m_ShadowMapTexture);
            m_CameraColorRT = new RenderTargetIdentifier(m_CameraColorTexture);
            m_CameraDepthRT = new RenderTargetIdentifier(m_CameraDepthTexture);
            m_CameraCopyDepthRT = new RenderTargetIdentifier(m_CameraCopyDepthTexture);
            m_PostProcessRenderContext = new PostProcessRenderContext();

            m_CopyTextureSupport = SystemInfo.copyTextureSupport;

            // Let engine know we have MSAA on for cases where we support MSAA backbuffer
            if (QualitySettings.antiAliasing != m_Asset.MSAASampleCount)
                QualitySettings.antiAliasing = m_Asset.MSAASampleCount;

            Shader.globalRenderPipeline = "LightweightPipeline";

            m_BlitQuad = LightweightUtils.CreateQuadMesh(false);
            m_BlitMaterial = new Material(m_Asset.BlitShader)
            {
                hideFlags = HideFlags.HideAndDontSave
            };

            m_CopyDepthMaterial = new Material(m_Asset.CopyDepthShader)
            {
                hideFlags = HideFlags.HideAndDontSave
            };
        }

        public override void Dispose()
        {
            base.Dispose();

            Shader.globalRenderPipeline = "";
            if (m_LightIndexListBuffer != null)
            {
                m_LightIndexListBuffer.Dispose();
                m_LightIndexListBuffer = null;
            }
        }

        CullResults m_CullResults;
        public override void Render(ScriptableRenderContext context, Camera[] cameras)
        {
            base.Render(context, cameras);

            bool stereoEnabled = XRSettings.isDeviceActive;

            // TODO: This is at the moment required for all pipes. We should not implicitly change user project settings
            // instead this should be forced when using SRP, since all SRP use linear lighting.
            GraphicsSettings.lightsUseLinearIntensity = true;

            SetupPerFrameShaderConstants(ref context);

            // Sort cameras array by camera depth
            Array.Sort(cameras, m_CameraComparer);
            foreach (Camera camera in cameras)
            {
                m_CurrCamera = camera;

                ScriptableCullingParameters cullingParameters;
                if (!CullResults.GetCullingParameters(m_CurrCamera, stereoEnabled, out cullingParameters))
                    continue;

                cullingParameters.shadowDistance = Mathf.Min(m_ShadowSettings.maxShadowDistance,
                    m_CurrCamera.farClipPlane);

#if UNITY_EDITOR
                // Emit scene view UI
                if (camera.cameraType == CameraType.SceneView)
                    ScriptableRenderContext.EmitWorldGeometryForSceneView(camera);
#endif

                CullResults.Cull(ref cullingParameters, context, ref m_CullResults);
                VisibleLight[] visibleLights = m_CullResults.visibleLights.ToArray();

                LightData lightData;
                InitializeLightData(visibleLights, out lightData);

                ShadowPass(visibleLights, ref context, ref lightData);
                ForwardPass(visibleLights, ref context, ref lightData, stereoEnabled);

                // Release temporary RT
                var cmd = CommandBufferPool.Get("After Camera Render");
                cmd.ReleaseTemporaryRT(m_ShadowMapTexture);
                cmd.ReleaseTemporaryRT(m_CameraColorTexture);
                cmd.ReleaseTemporaryRT(m_CameraDepthTexture);
                cmd.ReleaseTemporaryRT(m_CameraCopyDepthTexture);
                context.ExecuteCommandBuffer(cmd);
                CommandBufferPool.Release(cmd);

                context.Submit();
            }
        }

        private void ShadowPass(VisibleLight[] visibleLights, ref ScriptableRenderContext context, ref LightData lightData)
        {
            if (m_Asset.AreShadowsEnabled() && lightData.mainLightIndex != -1)
            {
                VisibleLight mainLight = visibleLights[lightData.mainLightIndex];
                if (mainLight.light.shadows != LightShadows.None)
                {
                    // There's no way to map shadow light indices. We need to pass in the original unsorted index.
                    // If no additional lights then no light sorting is performed and the indices match.
                    int shadowOriginalIndex = (lightData.hasAdditionalLights) ? GetLightUnsortedIndex(lightData.mainLightIndex) : lightData.mainLightIndex;
                    lightData.shadowsRendered = RenderShadows(ref m_CullResults, ref mainLight,
                        shadowOriginalIndex, ref context);
                }
            }
        }

        private void ForwardPass(VisibleLight[] visibleLights, ref ScriptableRenderContext context, ref LightData lightData, bool stereoEnabled)
        {
            FrameRenderingConfiguration frameRenderingConfiguration;
            SetupFrameRendering(out frameRenderingConfiguration);
            SetupIntermediateResources(frameRenderingConfiguration, ref context);
            SetupShaderConstants(visibleLights, ref context, ref lightData);

            // SetupCameraProperties does the following:
            // Setup Camera RenderTarget and Viewport
            // VR Camera Setup and SINGLE_PASS_STEREO props
            // Setup camera view, proj and their inv matrices.
            // Setup properties: _WorldSpaceCameraPos, _ProjectionParams, _ScreenParams, _ZBufferParams, unity_OrthoParams
            // Setup camera world clip planes props
            // setup HDR keyword
            // Setup global time properties (_Time, _SinTime, _CosTime)
            context.SetupCameraProperties(m_CurrCamera, stereoEnabled);

            RendererConfiguration rendererSettings = GetRendererSettings(ref lightData);

            BeginForwardRendering(ref context, frameRenderingConfiguration);
            RenderOpaques(ref context, rendererSettings);
            AfterOpaque(ref context, frameRenderingConfiguration);
            RenderTransparents(ref context, rendererSettings);
            AfterTransparent(ref context, frameRenderingConfiguration);
            EndForwardRendering(ref context, frameRenderingConfiguration);
        }

        private void RenderOpaques(ref ScriptableRenderContext context, RendererConfiguration settings)
        {
            var opaqueDrawSettings = new DrawRendererSettings(m_CurrCamera, m_LitPassName);
            opaqueDrawSettings.sorting.flags = SortFlags.CommonOpaque;
            opaqueDrawSettings.rendererConfiguration = settings;

            var opaqueFilterSettings = new FilterRenderersSettings(true)
            {
                renderQueueRange = RenderQueueRange.opaque
            };

            context.DrawRenderers(m_CullResults.visibleRenderers, ref opaqueDrawSettings, opaqueFilterSettings);
            context.DrawSkybox(m_CurrCamera);
        }

        private void AfterOpaque(ref ScriptableRenderContext context, FrameRenderingConfiguration config)
        {
            if (!LightweightUtils.HasFlag(config, FrameRenderingConfiguration.RequireDepth))
                return;

            CommandBuffer cmd = CommandBufferPool.Get("After Opaque");
            cmd.SetGlobalTexture(m_CameraDepthTexture, m_CameraDepthRT);

            // When soft particles are enabled we have to copy depth to another RT so we can read and write to depth
            if (m_Asset.SupportsSoftParticles)
            {
                RenderTargetIdentifier colorRT = (m_CurrCamera.targetTexture != null) ? BuiltinRenderTextureType.CameraTarget : m_CameraColorRT;
                CopyTexture(cmd, m_CameraDepthRT, m_CameraCopyDepthTexture);
                SetupRenderTargets(cmd, colorRT, m_CameraCopyDepthRT);
            }

            // Only takes effect if custom BeforeTransparent PostProcessing effects are active
            if (LightweightUtils.HasFlag(config, FrameRenderingConfiguration.PostProcess))
                RenderPostProcess(cmd , true);

            context.ExecuteCommandBuffer(cmd);
            CommandBufferPool.Release(cmd);
        }

        private void AfterTransparent(ref ScriptableRenderContext context, FrameRenderingConfiguration config)
        {
            if (!LightweightUtils.HasFlag(config, FrameRenderingConfiguration.PostProcess))
                return;

            CommandBuffer cmd = CommandBufferPool.Get("After Transparent");
            RenderPostProcess(cmd, false);
            context.ExecuteCommandBuffer(cmd);
            CommandBufferPool.Release(cmd);
        }

        private void RenderTransparents(ref ScriptableRenderContext context, RendererConfiguration config)
        {
            var transparentSettings = new DrawRendererSettings(m_CurrCamera, m_LitPassName);
            transparentSettings.SetShaderPassName(1, m_UnlitPassName);
            transparentSettings.sorting.flags = SortFlags.CommonTransparent;
            transparentSettings.rendererConfiguration = config;

            var transparentFilterSettings = new FilterRenderersSettings(true)
            {
                renderQueueRange = RenderQueueRange.transparent
            };

            context.DrawRenderers(m_CullResults.visibleRenderers, ref transparentSettings, transparentFilterSettings);
        }

        private void BuildShadowSettings()
        {
            m_ShadowSettings = ShadowSettings.Default;
            m_ShadowSettings.directionalLightCascadeCount = m_Asset.CascadeCount;

            m_ShadowSettings.shadowAtlasWidth = m_Asset.ShadowAtlasResolution;
            m_ShadowSettings.shadowAtlasHeight = m_Asset.ShadowAtlasResolution;
            m_ShadowSettings.maxShadowDistance = m_Asset.ShadowDistance;

            switch (m_ShadowSettings.directionalLightCascadeCount)
            {
                case 1:
                    m_ShadowSettings.directionalLightCascades = new Vector3(1.0f, 0.0f, 0.0f);
                    break;

                case 2:
                    m_ShadowSettings.directionalLightCascades = new Vector3(m_Asset.Cascade2Split, 1.0f, 0.0f);
                    break;

                default:
                    m_ShadowSettings.directionalLightCascades = m_Asset.Cascade4Split;
                    break;
            }
        }

        private void SetupFrameRendering(out FrameRenderingConfiguration configuration)
        {
            configuration = (XRSettings.enabled) ? FrameRenderingConfiguration.Stereo : FrameRenderingConfiguration.None;
            if (XRSettings.enabled && XRSettings.eyeTextureDesc.dimension == TextureDimension.Tex2DArray)
                m_IntermediateTextureArray = true;
            else
                m_IntermediateTextureArray = false;

            bool intermediateTexture = m_CurrCamera.targetTexture != null || m_CurrCamera.cameraType == CameraType.SceneView ||
                                            m_Asset.RenderScale < 1.0f || m_CurrCamera.allowHDR;

            m_ColorFormat = m_CurrCamera.allowHDR ? RenderTextureFormat.ARGBHalf : RenderTextureFormat.ARGB32;

            m_CameraPostProcessLayer = m_CurrCamera.GetComponent<PostProcessLayer>();
            bool postProcessEnabled = m_CameraPostProcessLayer != null && m_CameraPostProcessLayer.enabled;
            if (postProcessEnabled || m_Asset.SupportsSoftParticles)
            {
                configuration |= FrameRenderingConfiguration.RequireDepth;
                intermediateTexture = true;

                if (postProcessEnabled)
                    configuration |= FrameRenderingConfiguration.PostProcess;
            }
            // When post process or soft particles are enabled we disable msaa due to lack of depth resolve
            // One can still use PostFX AA
            else if (m_CurrCamera.allowMSAA && m_Asset.MSAASampleCount > 1)
            {
                configuration |= FrameRenderingConfiguration.Msaa;
                intermediateTexture = !LightweightUtils.PlatformSupportsMSAABackBuffer();
            }

            Rect cameraRect = m_CurrCamera.rect;
            if (cameraRect.x > 0.0f || cameraRect.y > 0.0f || cameraRect.width < 1.0f || cameraRect.height < 1.0f)
                intermediateTexture = true;
            else
                configuration |= FrameRenderingConfiguration.DefaultViewport;

            if (intermediateTexture)
                configuration |= FrameRenderingConfiguration.IntermediateTexture;
        }

        private void SetupIntermediateResources(FrameRenderingConfiguration renderingConfig, ref ScriptableRenderContext context)
        {
            CommandBuffer cmd = CommandBufferPool.Get("Setup Intermediate Resources");

            float renderScale = (m_CurrCamera.cameraType == CameraType.Game) ? m_Asset.RenderScale : 1.0f;
            int rtWidth = (int)((float)m_CurrCamera.pixelWidth * renderScale);
            int rtHeight = (int)((float)m_CurrCamera.pixelHeight * renderScale);
            int msaaSamples = (LightweightUtils.HasFlag(renderingConfig, FrameRenderingConfiguration.Msaa)) ? m_Asset.MSAASampleCount : 1;

            if (LightweightUtils.HasFlag(renderingConfig, FrameRenderingConfiguration.IntermediateTexture))
            {
                if (LightweightUtils.HasFlag(renderingConfig, FrameRenderingConfiguration.Stereo))
                {
                    RenderTextureDescriptor rtDesc = new RenderTextureDescriptor();
                    rtDesc = XRSettings.eyeTextureDesc;
                    rtDesc.colorFormat = m_ColorFormat;
                    rtDesc.msaaSamples = msaaSamples;

                    cmd.GetTemporaryRT(m_CameraColorTexture, rtDesc, FilterMode.Bilinear);
                }
                else if (m_CurrCamera.targetTexture == null)
                {
                    cmd.GetTemporaryRT(m_CameraColorTexture, rtWidth, rtHeight, kCameraDepthBufferBits,
                        FilterMode.Bilinear, m_ColorFormat, RenderTextureReadWrite.Default, msaaSamples);
                }
            }

            if (LightweightUtils.HasFlag(renderingConfig, FrameRenderingConfiguration.RequireDepth))
            {
                cmd.GetTemporaryRT(m_CameraDepthTexture, rtWidth, rtHeight, kCameraDepthBufferBits, FilterMode.Bilinear, RenderTextureFormat.Depth);
                if (m_Asset.SupportsSoftParticles)
                    cmd.GetTemporaryRT(m_CameraCopyDepthTexture, rtWidth, rtHeight, kCameraDepthBufferBits, FilterMode.Bilinear, RenderTextureFormat.Depth);
            }

            context.ExecuteCommandBuffer(cmd);
            CommandBufferPool.Release(cmd);
        }

        private void SetupShaderConstants(VisibleLight[] visibleLights, ref ScriptableRenderContext context, ref LightData lightData)
        {
            CommandBuffer cmd = CommandBufferPool.Get("SetupShaderConstants");
            SetupShaderLightConstants(cmd, visibleLights, ref lightData, ref m_CullResults, ref context);
            SetShaderKeywords(cmd, ref lightData, visibleLights);
            context.ExecuteCommandBuffer(cmd);
            CommandBufferPool.Release(cmd);
        }

        private void InitializeLightData(VisibleLight[] visibleLights, out LightData lightData)
        {
            int visibleLightsCount = visibleLights.Length;
            m_SortedLightIndexMap.Clear();

            // kMaxPerObjectLights + 1 main light
            int maxSupportedPixelLights = Math.Min(m_Asset.MaxSupportedPixelLights, kMaxPerObjectLights + 1);
            int maxPixelLights = Math.Min(maxSupportedPixelLights, visibleLightsCount);

            if (maxPixelLights <= 1)
            {
                lightData.mainLightIndex = maxPixelLights - 1;
                lightData.additionalPixelLightsCount = 0;
            }
            else
            {
                lightData.mainLightIndex = SortLights(visibleLights);
                lightData.additionalPixelLightsCount = maxPixelLights - 1;
            }

            lightData.vertexLightsCount = (m_Asset.SupportsVertexLight) ? Math.Min(4, Math.Min(visibleLightsCount - maxPixelLights, kMaxPerObjectLights)) : 0;
            lightData.hasAdditionalLights = (lightData.additionalPixelLightsCount + lightData.vertexLightsCount) > 0;
            lightData.shadowsRendered = false;
        }

        private int SortLights(VisibleLight[] visibleLights)
        {
            int totalVisibleLights = visibleLights.Length;

            Dictionary<int, int> visibleLightsIDMap = new Dictionary<int, int>();
            for (int i = 0; i < totalVisibleLights; ++i)
                visibleLightsIDMap.Add(visibleLights[i].light.GetInstanceID(), i);

            // Sorts light so we have all directionals first, then local lights.
            // Directionals are sorted further by shadow, cookie and intensity
            // Locals are sorted further by shadow, cookie and distance to camera
            m_LightCompararer.CurrCamera = m_CurrCamera;
            Array.Sort(visibleLights, m_LightCompararer);

            for (int i = 0; i < totalVisibleLights; ++i)
                m_SortedLightIndexMap.Add(visibleLightsIDMap[visibleLights[i].light.GetInstanceID()]);

            return GetMainLight(visibleLights);
        }

        // How main light is decided:
        // If shadows enabled, main light is always a shadow casting light. Directional has priority over local lights.
        // Otherwise directional lights have priority based on cookie support and intensity
        // If no directional light in the scene local lights based on cookie support and distance to camera
        private int GetMainLight(VisibleLight[] visibleLights)
        {
            int totalVisibleLights = visibleLights.Length;
            bool shadowsEnabled = m_Asset.AreShadowsEnabled();

            // If shadows are supported and the first visible light has shadows then this is main light
            if (shadowsEnabled && visibleLights[0].light.shadows != LightShadows.None)
                return 0;

            // We don't have any directional shadow casting light, skip until we find the first non directional light
            int lightIndex = 0;
            while (lightIndex < totalVisibleLights && visibleLights[lightIndex].lightType == LightType.Directional)
                lightIndex++;

            // If first non-directional light has shadows we return it, otherwise we return first light
            return (lightIndex < totalVisibleLights && visibleLights[lightIndex].light.shadows != LightShadows.None) ? lightIndex : 0;
        }

        private void InitializeLightConstants(VisibleLight[] lights, int lightIndex, out Vector4 lightPos, out Vector4 lightColor, out Vector4 lightSpotDir,
            out Vector4 lightAttenuationParams)
        {
            lightPos = Vector4.zero;
            lightColor = Color.black;
            lightAttenuationParams = new Vector4(0.0f, 1.0f, 0.0f, 0.0f);
            lightSpotDir = new Vector4(0.0f, 0.0f, 1.0f, 0.0f);

            // When no lights are available in the pipeline or maxPixelLights is set to 0
            // In this case we want to initialize the lightData to default values and return
            if (lightIndex < 0)
                return;

            VisibleLight light = lights[lightIndex];
            if (light.lightType == LightType.Directional)
            {
                Vector4 dir = -light.localToWorld.GetColumn(2);
                lightPos = new Vector4(dir.x, dir.y, dir.z, 0.0f);
            }
            else
            {
                Vector4 pos = light.localToWorld.GetColumn(3);
                lightPos = new Vector4(pos.x, pos.y, pos.z, 1.0f);
            }

            lightColor = light.finalColor;

            float rangeSq = light.range * light.range;
            float quadAtten = 0.0f;
            if (light.lightType != LightType.Directional)
                quadAtten = (m_Asset.AttenuationTexture != null) ? 1.0f : 25.0f / rangeSq;

            if (light.lightType == LightType.Spot)
            {
                Vector4 dir = light.localToWorld.GetColumn(2);
                lightSpotDir = new Vector4(-dir.x, -dir.y, -dir.z, 0.0f);

                float spotAngle = Mathf.Deg2Rad * light.spotAngle;
                float cosOuterAngle = Mathf.Cos(spotAngle * 0.5f);
                float cosInneAngle = Mathf.Cos(spotAngle * 0.25f);
                float angleRange = cosInneAngle - cosOuterAngle;
                lightAttenuationParams = new Vector4(cosOuterAngle,
                    Mathf.Approximately(angleRange, 0.0f) ? 1.0f : angleRange, quadAtten, rangeSq);
            }
            else
            {
                lightSpotDir = new Vector4(0.0f, 0.0f, 1.0f, 0.0f);
                lightAttenuationParams = new Vector4(-1.0f, 1.0f, quadAtten, rangeSq);
            }
        }

        private void SetupPerFrameShaderConstants(ref ScriptableRenderContext context)
        {
            // When glossy reflections are OFF in the shader we set a constant color to use as indirect specular
            SphericalHarmonicsL2 ambientSH = RenderSettings.ambientProbe;
            Vector4 glossyEnvColor = new Vector4(ambientSH[0, 0], ambientSH[1, 0], ambientSH[2, 0]) * RenderSettings.reflectionIntensity;

            CommandBuffer cmd = CommandBufferPool.Get("SetupPerFrameConstants");
            cmd.SetGlobalVector(PerFrameBuffer._GlossyEnvironmentColor, glossyEnvColor);
            if (m_Asset.AttenuationTexture != null) cmd.SetGlobalTexture(PerFrameBuffer._AttenuationTexture, m_Asset.AttenuationTexture);
            context.ExecuteCommandBuffer(cmd);
            CommandBufferPool.Release (cmd);
        }

        private void SetupShaderLightConstants(CommandBuffer cmd, VisibleLight[] lights, ref LightData lightData, ref CullResults cullResults, ref ScriptableRenderContext context)
        {
            // Main light has an optimized shader path for main light. This will benefit games that only care about a single light.
            // Lightweight pipeline also supports only a single shadow light, if available it will be the main light.
            if (lightData.mainLightIndex != -1)
            {
                SetupMainLightConstants (cmd, lights, lightData.mainLightIndex, ref context);
                if (lightData.shadowsRendered)
                    SetupShadowShaderConstants (cmd, ref context, ref lights[lightData.mainLightIndex], m_ShadowCasterCascadesCount);
            }

            if (lightData.hasAdditionalLights)
                SetupAdditionalListConstants(cmd, lights, ref lightData, ref context);
        }

        private void SetupMainLightConstants(CommandBuffer cmd, VisibleLight[] lights, int lightIndex, ref ScriptableRenderContext context)
        {
            Vector4 lightPos, lightColor, lightSpotDir, lightAttenuationParams;
            InitializeLightConstants(lights, lightIndex, out lightPos, out lightColor, out lightSpotDir, out lightAttenuationParams);

            cmd.SetGlobalVector(PerCameraBuffer._MainLightPosition, lightPos);
            cmd.SetGlobalColor(PerCameraBuffer._MainLightColor, lightColor);
            cmd.SetGlobalVector(PerCameraBuffer._MainLightSpotDir, lightSpotDir);
            cmd.SetGlobalVector(PerCameraBuffer._MainLightAttenuationParams, lightAttenuationParams);
        }

        private void SetupAdditionalListConstants(CommandBuffer cmd, VisibleLight[] lights, ref LightData lightData, ref ScriptableRenderContext context)
        {
            int additionalLightIndex = 0;

            // We need to update per-object light list with the proper map to our global additional light buffer
            // First we initialize all lights in the map to -1 to tell the system to discard main light index and
            // remaining lights in the scene that don't fit the max additional light buffer (kMaxVisibileAdditionalLights)
            int[] perObjectLightIndexMap = m_CullResults.GetLightIndexMap();
            for (int i = 0; i < lights.Length; ++i)
                perObjectLightIndexMap[i] = -1;

            for (int i = 0; i < lights.Length && additionalLightIndex < kMaxVisibleAdditionalLights; ++i)
            {
                if (i != lightData.mainLightIndex)
                {
                    // The engine performs per-object light culling and initialize 8 light indices into two vec4 constants unity_4LightIndices0 and unity_4LightIndices1.
                    // In the shader we iterate over each visible light using the indices provided in these constants to index our global light buffer
                    // ex: first light position would be m_LightPosisitions[unity_4LightIndices[0]];

                    // However since we sorted the lights we need to tell the engine how to map the original/unsorted indices to our global buffer
                    // We do it by settings the perObjectLightIndexMap to the appropriate additionalLightIndex.
                    perObjectLightIndexMap[GetLightUnsortedIndex(i)] = additionalLightIndex;
                    InitializeLightConstants(lights, i, out m_LightPositions[additionalLightIndex],
                            out m_LightColors[additionalLightIndex],
                            out m_LightSpotDirections[additionalLightIndex],
                            out m_LightAttenuations[additionalLightIndex]);
                    additionalLightIndex++;
                }
            }
            m_CullResults.SetLightIndexMap(perObjectLightIndexMap);

            cmd.SetGlobalVector(PerCameraBuffer._AdditionalLightCount, new Vector4 (lightData.additionalPixelLightsCount, lightData.vertexLightsCount, 0.0f, 0.0f));
            cmd.SetGlobalVectorArray (PerCameraBuffer._AdditionalLightPosition, m_LightPositions);
            cmd.SetGlobalVectorArray (PerCameraBuffer._AdditionalLightColor, m_LightColors);
            cmd.SetGlobalVectorArray (PerCameraBuffer._AdditionalLightAttenuationParams, m_LightAttenuations);
            cmd.SetGlobalVectorArray (PerCameraBuffer._AdditionalLightSpotDir, m_LightSpotDirections);
        }

        private void SetupShadowShaderConstants(CommandBuffer cmd, ref ScriptableRenderContext context, ref VisibleLight shadowLight, int cascadeCount)
        {
            Vector3 shadowLightDir = Vector3.Normalize(shadowLight.localToWorld.GetColumn(2));

            float bias = shadowLight.light.shadowBias * 0.1f;
            float normalBias = shadowLight.light.shadowNormalBias;
            float shadowResolution = m_ShadowSlices[0].shadowResolution;

            const int maxShadowCascades = 4;
            Matrix4x4[] shadowMatrices = new Matrix4x4[maxShadowCascades];
            for (int i = 0; i < cascadeCount; ++i)
                shadowMatrices[i] = (cascadeCount >= i) ? m_ShadowSlices[i].shadowTransform : Matrix4x4.identity;

            // TODO: shadow resolution per cascade in case cascades endup being supported.
            float invShadowResolution = 1.0f / shadowResolution;
            float[] pcfKernel =
            {
                -0.5f * invShadowResolution, 0.5f * invShadowResolution,
                0.5f * invShadowResolution, 0.5f * invShadowResolution,
                -0.5f * invShadowResolution, -0.5f * invShadowResolution,
                0.5f * invShadowResolution, -0.5f * invShadowResolution
            };

            cmd.SetGlobalMatrixArray("_WorldToShadow", shadowMatrices);
            cmd.SetGlobalVectorArray("_DirShadowSplitSpheres", m_DirectionalShadowSplitDistances);
            cmd.SetGlobalVector("_ShadowLightDirection", new Vector4(-shadowLightDir.x, -shadowLightDir.y, -shadowLightDir.z, 0.0f));
            cmd.SetGlobalVector("_ShadowData", new Vector4(0.0f, bias, normalBias, 0.0f));
            cmd.SetGlobalFloatArray("_PCFKernel", pcfKernel);
        }

        private void SetShaderKeywords(CommandBuffer cmd, ref LightData lightData, VisibleLight[] visibleLights)
        {
            LightweightUtils.SetKeyword(cmd, "_LIGHTWEIGHT_FORCE_LINEAR", m_Asset.ForceLinearRendering);
            LightweightUtils.SetKeyword(cmd, "_VERTEX_LIGHTS", lightData.vertexLightsCount > 0);
            LightweightUtils.SetKeyword(cmd, "_ATTENUATION_TEXTURE", m_Asset.AttenuationTexture != null);

            int mainLightIndex = lightData.mainLightIndex;
            LightweightUtils.SetKeyword (cmd, "_MAIN_DIRECTIONAL_LIGHT", mainLightIndex != -1 && visibleLights[mainLightIndex].lightType == LightType.Directional);
            LightweightUtils.SetKeyword (cmd, "_MAIN_SPOT_LIGHT", mainLightIndex != -1 && visibleLights[mainLightIndex].lightType == LightType.Spot);
            LightweightUtils.SetKeyword (cmd, "_MAIN_POINT_LIGHT", mainLightIndex != -1 && visibleLights[mainLightIndex].lightType == LightType.Point);
            LightweightUtils.SetKeyword(cmd, "_ADDITIONAL_PIXEL_LIGHTS", lightData.additionalPixelLightsCount > 0);

            string[] shadowKeywords = new string[] { "_HARD_SHADOWS", "_SOFT_SHADOWS", "_HARD_SHADOWS_CASCADES", "_SOFT_SHADOWS_CASCADES" };
            for (int i = 0; i < shadowKeywords.Length; ++i)
                cmd.DisableShaderKeyword(shadowKeywords[i]);

            if (m_Asset.AreShadowsEnabled() && lightData.shadowsRendered)
            {
                int keywordIndex = (int)m_Asset.ShadowSetting - 1;
                if (m_Asset.CascadeCount > 1)
                    keywordIndex += 2;
                cmd.EnableShaderKeyword(shadowKeywords[keywordIndex]);
            }

            LightweightUtils.SetKeyword(cmd, "SOFTPARTICLES_ON", m_Asset.SupportsSoftParticles);
        }

        private bool RenderShadows(ref CullResults cullResults, ref VisibleLight shadowLight, int shadowLightIndex, ref ScriptableRenderContext context)
        {
            m_ShadowCasterCascadesCount = m_ShadowSettings.directionalLightCascadeCount;

            if (shadowLight.lightType == LightType.Spot)
                m_ShadowCasterCascadesCount = 1;

            int shadowResolution = GetMaxTileResolutionInAtlas(m_ShadowSettings.shadowAtlasWidth, m_ShadowSettings.shadowAtlasHeight, m_ShadowCasterCascadesCount);

            Bounds bounds;
            if (!cullResults.GetShadowCasterBounds(shadowLightIndex, out bounds))
                return false;

            var setRenderTargetCommandBuffer = CommandBufferPool.Get();
            setRenderTargetCommandBuffer.name = "Render packed shadows";
            setRenderTargetCommandBuffer.GetTemporaryRT(m_ShadowMapTexture, m_ShadowSettings.shadowAtlasWidth,
                m_ShadowSettings.shadowAtlasHeight, kShadowDepthBufferBits, FilterMode.Bilinear, RenderTextureFormat.Depth);
            setRenderTargetCommandBuffer.SetRenderTarget(m_ShadowMapRT);
            setRenderTargetCommandBuffer.ClearRenderTarget(true, true, Color.black);
            context.ExecuteCommandBuffer(setRenderTargetCommandBuffer);
            CommandBufferPool.Release(setRenderTargetCommandBuffer);

            float shadowNearPlane = m_Asset.ShadowNearOffset;
            Vector3 splitRatio = m_ShadowSettings.directionalLightCascades;

            Matrix4x4 view, proj;
            var settings = new DrawShadowsSettings(cullResults, shadowLightIndex);
            bool needRendering = false;

            if (shadowLight.lightType == LightType.Spot)
            {
                needRendering = cullResults.ComputeSpotShadowMatricesAndCullingPrimitives(shadowLightIndex, out view, out proj,
                        out settings.splitData);

                if (!needRendering)
                    return false;

                SetupShadowSliceTransform(0, shadowResolution, proj, view);
                RenderShadowSlice(ref context, 0, proj, view, settings);
            }
            else if (shadowLight.lightType == LightType.Directional)
            {
                for (int cascadeIdx = 0; cascadeIdx < m_ShadowCasterCascadesCount; ++cascadeIdx)
                {
                    needRendering = cullResults.ComputeDirectionalShadowMatricesAndCullingPrimitives(shadowLightIndex,
                            cascadeIdx, m_ShadowCasterCascadesCount, splitRatio, shadowResolution, shadowNearPlane, out view, out proj,
                            out settings.splitData);

                    m_DirectionalShadowSplitDistances[cascadeIdx] = settings.splitData.cullingSphere;
                    m_DirectionalShadowSplitDistances[cascadeIdx].w *= settings.splitData.cullingSphere.w;

                    if (!needRendering)
                        return false;

                    SetupShadowSliceTransform(cascadeIdx, shadowResolution, proj, view);
                    RenderShadowSlice(ref context, cascadeIdx, proj, view, settings);
                }
            }
            else
            {
                Debug.LogWarning("Only spot and directional shadow casters are supported in lightweight pipeline");
                return false;
            }

            return true;
        }

        private void SetupShadowSliceTransform(int cascadeIndex, int shadowResolution, Matrix4x4 proj, Matrix4x4 view)
        {
            // Assumes MAX_CASCADES = 4
            m_ShadowSlices[cascadeIndex].atlasX = (cascadeIndex % 2) * shadowResolution;
            m_ShadowSlices[cascadeIndex].atlasY = (cascadeIndex / 2) * shadowResolution;
            m_ShadowSlices[cascadeIndex].shadowResolution = shadowResolution;
            m_ShadowSlices[cascadeIndex].shadowTransform = Matrix4x4.identity;

            var matScaleBias = Matrix4x4.identity;
            matScaleBias.m00 = 0.5f;
            matScaleBias.m11 = 0.5f;
            matScaleBias.m22 = 0.5f;
            matScaleBias.m03 = 0.5f;
            matScaleBias.m23 = 0.5f;
            matScaleBias.m13 = 0.5f;

            // Later down the pipeline the proj matrix will be scaled to reverse-z in case of DX.
            // We need account for that scale in the shadowTransform.
            if (SystemInfo.usesReversedZBuffer)
                matScaleBias.m22 = -0.5f;

            var matTile = Matrix4x4.identity;
            matTile.m00 = (float)m_ShadowSlices[cascadeIndex].shadowResolution /
                (float)m_ShadowSettings.shadowAtlasWidth;
            matTile.m11 = (float)m_ShadowSlices[cascadeIndex].shadowResolution /
                (float)m_ShadowSettings.shadowAtlasHeight;
            matTile.m03 = (float)m_ShadowSlices[cascadeIndex].atlasX / (float)m_ShadowSettings.shadowAtlasWidth;
            matTile.m13 = (float)m_ShadowSlices[cascadeIndex].atlasY / (float)m_ShadowSettings.shadowAtlasHeight;

            m_ShadowSlices[cascadeIndex].shadowTransform = matTile * matScaleBias * proj * view;
        }

        private void RenderShadowSlice(ref ScriptableRenderContext context, int cascadeIndex,
            Matrix4x4 proj, Matrix4x4 view, DrawShadowsSettings settings)
        {
            var buffer = CommandBufferPool.Get("Prepare Shadowmap Slice");
            buffer.SetViewport(new Rect(m_ShadowSlices[cascadeIndex].atlasX, m_ShadowSlices[cascadeIndex].atlasY,
                    m_ShadowSlices[cascadeIndex].shadowResolution, m_ShadowSlices[cascadeIndex].shadowResolution));
            buffer.SetViewProjectionMatrices(view, proj);
            context.ExecuteCommandBuffer(buffer);

            context.DrawShadows(ref settings);
            CommandBufferPool.Release(buffer);
        }

        private int GetMaxTileResolutionInAtlas(int atlasWidth, int atlasHeight, int tileCount)
        {
            int resolution = Mathf.Min(atlasWidth, atlasHeight);
            if (tileCount > Mathf.Log(resolution))
            {
                Debug.LogError(
                    String.Format(
                        "Cannot fit {0} tiles into current shadowmap atlas of size ({1}, {2}). ShadowMap Resolution set to zero.",
                        tileCount, atlasWidth, atlasHeight));
                return 0;
            }

            int currentTileCount = atlasWidth / resolution * atlasHeight / resolution;
            while (currentTileCount < tileCount)
            {
                resolution = resolution >> 1;
                currentTileCount = atlasWidth / resolution * atlasHeight / resolution;
            }
            return resolution;
        }

        private void BeginForwardRendering(ref ScriptableRenderContext context, FrameRenderingConfiguration renderingConfig)
        {
            RenderTargetIdentifier colorRT = BuiltinRenderTextureType.CameraTarget;
            RenderTargetIdentifier depthRT = BuiltinRenderTextureType.None;

            if (LightweightUtils.HasFlag(renderingConfig, FrameRenderingConfiguration.Stereo))
                context.StartMultiEye(m_CurrCamera);

            CommandBuffer cmd = CommandBufferPool.Get("SetCameraRenderTarget");
            if (LightweightUtils.HasFlag(renderingConfig, FrameRenderingConfiguration.IntermediateTexture))
            {
                if (m_CurrCamera.targetTexture == null)
                    colorRT = m_CameraColorRT;

                if (LightweightUtils.HasFlag(renderingConfig, FrameRenderingConfiguration.RequireDepth))
                    depthRT = m_CameraDepthRT;
            }

            SetupRenderTargets(cmd, colorRT, depthRT);

            // Clear RenderTarget to avoid tile initialization on mobile GPUs
            // https://community.arm.com/graphics/b/blog/posts/mali-performance-2-how-to-correctly-handle-framebuffers
            if (m_CurrCamera.clearFlags != CameraClearFlags.Nothing)
            {
                bool clearDepth = (m_CurrCamera.clearFlags != CameraClearFlags.Nothing);
                bool clearColor = (m_CurrCamera.clearFlags == CameraClearFlags.Color || m_CurrCamera.clearFlags == CameraClearFlags.Skybox);
                cmd.ClearRenderTarget(clearDepth, clearColor, m_CurrCamera.backgroundColor.linear);
            }

            context.ExecuteCommandBuffer(cmd);
            CommandBufferPool.Release(cmd);
        }

        private void EndForwardRendering(ref ScriptableRenderContext context, FrameRenderingConfiguration renderingConfig)
        {
            // No additional rendering needs to be done if this is an offscren rendering camera (unless camera is scene view)
            if (m_CurrCamera.targetTexture != null && m_CurrCamera.cameraType != CameraType.SceneView)
                return;

            var cmd = CommandBufferPool.Get("Blit");
            if (m_IntermediateTextureArray)
            {
                cmd.SetRenderTarget(BuiltinRenderTextureType.CameraTarget, 0, CubemapFace.Unknown, -1);
                cmd.Blit(m_CameraColorRT, BuiltinRenderTextureType.CurrentActive);
            }
            else if (LightweightUtils.HasFlag(renderingConfig, FrameRenderingConfiguration.IntermediateTexture))
            {
                // If PostProcessing is enabled, it is already blit to CameraTarget.
                if (!LightweightUtils.HasFlag(renderingConfig, FrameRenderingConfiguration.PostProcess))
                    Blit(cmd, renderingConfig, BuiltinRenderTextureType.CurrentActive, BuiltinRenderTextureType.CameraTarget);
            }

            SetupRenderTargets(cmd, BuiltinRenderTextureType.CameraTarget, BuiltinRenderTextureType.None);

            context.ExecuteCommandBuffer(cmd);
            CommandBufferPool.Release(cmd);

            if (LightweightUtils.HasFlag(renderingConfig, FrameRenderingConfiguration.Stereo))
            {
                context.StopMultiEye(m_CurrCamera);
                context.StereoEndRender(m_CurrCamera);
            }
        }

        RendererConfiguration GetRendererSettings(ref LightData lightData)
        {
            RendererConfiguration settings = RendererConfiguration.PerObjectReflectionProbes | RendererConfiguration.PerObjectLightmaps | RendererConfiguration.PerObjectLightProbe;
            if (lightData.hasAdditionalLights)
                settings |= RendererConfiguration.PerObjectLightIndices8;
            return settings;
        }

        private void SetupRenderTargets(CommandBuffer cmd, RenderTargetIdentifier colorRT, RenderTargetIdentifier depthRT)
        {
            int depthSlice = (m_IntermediateTextureArray) ? -1 : 0;
            if (depthRT != BuiltinRenderTextureType.None)
                cmd.SetRenderTarget(colorRT, depthRT, 0, CubemapFace.Unknown, depthSlice);
            else
                cmd.SetRenderTarget(colorRT, 0, CubemapFace.Unknown, depthSlice);
        }

        private void RenderPostProcess(CommandBuffer cmd, bool opaqueOnly)
        {
            m_PostProcessRenderContext.Reset();
            m_PostProcessRenderContext.camera = m_CurrCamera;
            m_PostProcessRenderContext.source = BuiltinRenderTextureType.CurrentActive;
            m_PostProcessRenderContext.sourceFormat = m_ColorFormat;
            m_PostProcessRenderContext.destination = BuiltinRenderTextureType.CameraTarget;
            m_PostProcessRenderContext.command = cmd;
            m_PostProcessRenderContext.flip = true;

            if (opaqueOnly)
                m_CameraPostProcessLayer.RenderOpaqueOnly(m_PostProcessRenderContext);
            else
                m_CameraPostProcessLayer.Render(m_PostProcessRenderContext);
        }

        private int GetLightUnsortedIndex(int index)
        {
            Debug.Assert(index >= 0 && index < m_SortedLightIndexMap.Count, "Invalid index while accessing light index map. If you only have a single light in scene you should not try to map indices");
            return m_SortedLightIndexMap[index];
        }

        private void Blit(CommandBuffer cmd, FrameRenderingConfiguration renderingConfig, RenderTargetIdentifier sourceRT, RenderTargetIdentifier destRT, Material material = null)
        {
            if (LightweightUtils.HasFlag(renderingConfig, FrameRenderingConfiguration.DefaultViewport))
            {
                cmd.Blit(sourceRT, destRT, material);
            }
            else
            {
                if (m_BlitQuad == null)
                    m_BlitQuad = LightweightUtils.CreateQuadMesh(false);

                cmd.SetGlobalTexture(m_BlitTexID, sourceRT);
                cmd.SetRenderTarget(destRT);
                cmd.SetViewport(m_CurrCamera.pixelRect);
                cmd.DrawMesh(m_BlitQuad, Matrix4x4.identity, m_BlitMaterial);
            }
        }

        private void CopyTexture(CommandBuffer cmd, RenderTargetIdentifier sourceRT, RenderTargetIdentifier destRT)
        {
            if (m_CopyTextureSupport != CopyTextureSupport.None)
                cmd.CopyTexture(m_CameraDepthRT, m_CameraCopyDepthRT);
            else
                cmd.Blit(m_CameraDepthRT, m_CameraCopyDepthRT, m_CopyDepthMaterial);
        }
    }
}