OIT.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreMinimal.h"
#include "RendererInterface.h"
#include "RenderGraphResources.h"
#include "RenderResource.h"
 
class FViewInfo;
class FSortedIndexBuffer;
struct FMeshBatchElement;
struct FMeshBatchElementDynamicIndexBuffer;
class FViewInfo;
 
enum EOITPassType
{
    OITPass_None = 0,
    OITPass_RegularTranslucency = 1,
    OITPass_SeperateTranslucency = 2
};
 
enum class FTriangleSortingOrder
{
    FrontToBack,
    BackToFront,
};
 
// Sorted triangles data
struct FSortedTriangleData
{
    const FIndexBuffer* SourceIndexBuffer = nullptr;
    FSortedIndexBuffer* SortedIndexBuffer = nullptr;
 
    uint32 SortedFirstIndex = 0;
    uint32 SourceFirstIndex = 0;
    uint32 SourceBaseVertexIndex = 0;
    uint32 SourceMinVertexIndex = 0;
    uint32 SourceMaxVertexIndex = 0;
    uint32 NumPrimitives = 0;
    uint32 NumIndices = 0;
 
    EPrimitiveType SourcePrimitiveType = PT_TriangleList;
    EPrimitiveType SortedPrimitiveType = PT_TriangleList;
 
    bool IsValid() const { return SortedIndexBuffer != nullptr; }
};
 
// Order Independent Translucency pass data for a given translucent pass
struct FOITData
{
    EOITPassType PassType = OITPass_None;
    uint32 SupportedPass = 0;
    uint32 Method = 0;
    uint32 MaxSamplePerPixel = 0;
    uint32 MaxSideSamplePerPixel = 0;
    float TransmittanceThreshold = 0.f;
 
    FRDGTextureRef SampleDataTexture = nullptr;
    FRDGTextureRef SampleCountTexture = nullptr;
};
 
// Order Independent Translucency scene data
struct FOITSceneData
{
    /* Allocate sorted-triangle data for a instance */
    void Allocate(FRHICommandListBase& RHICmdList, EPrimitiveType PrimitiveType, const FMeshBatchElement& InMeshElement, FMeshBatchElementDynamicIndexBuffer& OutMeshElement);
 
    /* Deallocate sorted-triangle data */
    void Deallocate(FMeshBatchElement& OutMeshElement);
 
    TArray<FSortedTriangleData> Allocations;
    TArray<FSortedIndexBuffer*> FreeBuffers;
    TQueue<FSortedIndexBuffer*> PendingDeletes;
    TQueue<uint32> FreeSlots;
    uint32 FrameIndex = 0;
};
 
namespace OIT
{
    /* Return true if OIT sorted triangles is enabled/supported */
    bool IsSortedTrianglesEnabled(EShaderPlatform InPlatform);
 
    /* Return true if the current MeshBatch is compatible with per-instance sorted triangle */
    bool IsCompatible(const FMeshBatch& Mesh, ERHIFeatureLevel::Type InFeatureLevel);
 
    /* Return if OIT sorted pixel is enabled for the project*/
    bool IsSortedPixelsEnabledForProject(EShaderPlatform InPlatform);
 
    /* Return if OIT is enabled for the current runtime */
    bool IsSortedPixelsEnabled(const FViewInfo& InView);
    bool IsSortedPixelsEnabled(EShaderPlatform InPlatform); 
 
    /* Return if OIT is enabled for the translucent pass current pass */
    bool IsSortedPixelsEnabledForPass(EOITPassType PassType);
 
    /* Sort triangles of all instances whose has the sorted triangle option enabled */
    void AddSortTrianglesPass(FRDGBuilder& GraphBuilder, const FViewInfo& View, FOITSceneData& OITSceneData, FTriangleSortingOrder SortType);
 
    /* Create OIT data for translucent pass */
    FOITData CreateOITData(FRDGBuilder& GraphBuilder, const FViewInfo& View, EOITPassType PassType);
 
    /* Compose all OIT samples into the target color buffer */
    void AddOITComposePass(FRDGBuilder& GraphBuilder, const FViewInfo& View, FOITData& OITData, FRDGTextureRef SceneColorTexture);
    void AddOITComposePass(FRDGBuilder& GraphBuilder, const FViewInfo& View, FOITData& OITData, FRDGTextureRef LightingTexture, FRDGTextureRef ModulateTexture);
 
    /* Call on SceneRenderer OnRenderBegin */
    void OnRenderBegin(FOITSceneData& OITSceneData);
}