// Copyright Epic Games, Inc. All Rights Reserved.

#include "DBufferTextures.h"

#include "RendererUtils.h"
#include "RenderGraphUtils.h"
#include "SceneUtils.h"
#include "ScenePrivate.h"

bool FDBufferTextures::IsValid() const
{
	check(!DBufferA || (DBufferB && DBufferC));
	return HasBeenProduced(DBufferA);
}

EDecalDBufferMaskTechnique GetDBufferMaskTechnique(EShaderPlatform ShaderPlatform)
{
	const bool bWriteMaskDBufferMask = RHISupportsRenderTargetWriteMask(ShaderPlatform);
	const bool bPerPixelDBufferMask = FDataDrivenShaderPlatformInfo::GetSupportsPerPixelDBufferMask(ShaderPlatform);
	checkf(!bWriteMaskDBufferMask || !bPerPixelDBufferMask, TEXT("The WriteMask and PerPixel DBufferMask approaches cannot be enabled at the same time. They are mutually exclusive."));

	if (bWriteMaskDBufferMask)
	{
		return EDecalDBufferMaskTechnique::WriteMask;
	}
	else if (bPerPixelDBufferMask)
	{
		return EDecalDBufferMaskTechnique::PerPixel;
	}
	return EDecalDBufferMaskTechnique::Disabled;
}

FDBufferTextures CreateDBufferTextures(FRDGBuilder& GraphBuilder, FIntPoint Extent, EShaderPlatform ShaderPlatform)
{
	FDBufferTextures DBufferTextures;

	if (IsUsingDBuffers(ShaderPlatform))
	{
		const EDecalDBufferMaskTechnique DBufferMaskTechnique = GetDBufferMaskTechnique(ShaderPlatform);
		const ETextureCreateFlags WriteMaskFlags = DBufferMaskTechnique == EDecalDBufferMaskTechnique::WriteMask ? TexCreate_NoFastClearFinalize | TexCreate_DisableDCC : TexCreate_None;
		const ETextureCreateFlags BaseFlags = WriteMaskFlags | TexCreate_ShaderResource | TexCreate_RenderTargetable;
		const ERDGTextureFlags TextureFlags = DBufferMaskTechnique != EDecalDBufferMaskTechnique::Disabled
			? ERDGTextureFlags::MaintainCompression
			: ERDGTextureFlags::None;

		FRDGTextureDesc Desc = FRDGTextureDesc::Create2D(Extent, PF_B8G8R8A8, FClearValueBinding::None, BaseFlags);

		Desc.Flags = BaseFlags | GFastVRamConfig.DBufferA;
		Desc.ClearValue = FClearValueBinding::Black;
		DBufferTextures.DBufferA = GraphBuilder.CreateTexture(Desc, TEXT("DBufferA"), TextureFlags);

		Desc.Flags = BaseFlags | GFastVRamConfig.DBufferB;
		Desc.ClearValue = FClearValueBinding(FLinearColor(128.0f / 255.0f, 128.0f / 255.0f, 128.0f / 255.0f, 1));
		DBufferTextures.DBufferB = GraphBuilder.CreateTexture(Desc, TEXT("DBufferB"), TextureFlags);

		Desc.Flags = BaseFlags | GFastVRamConfig.DBufferC;
		Desc.ClearValue = FClearValueBinding(FLinearColor(0, 0, 0, 1));
		DBufferTextures.DBufferC = GraphBuilder.CreateTexture(Desc, TEXT("DBufferC"), TextureFlags);

		if (DBufferMaskTechnique == EDecalDBufferMaskTechnique::PerPixel)
		{
			// Note: 32bpp format is used here to utilize color compression hardware (same as other DBuffer targets).
			// This significantly reduces bandwidth for clearing, writing and reading on some GPUs.
			// While a smaller format, such as R8_UINT, will use less video memory, it will result in slower clears and higher bandwidth requirements.
			check(Desc.Format == PF_B8G8R8A8);
			Desc.Flags = TexCreate_ShaderResource | TexCreate_RenderTargetable;
			Desc.ClearValue = FClearValueBinding::Transparent;
			DBufferTextures.DBufferMask = GraphBuilder.CreateTexture(Desc, TEXT("DBufferMask"));
		}
	}

	return DBufferTextures;
}

FDBufferParameters GetDBufferParameters(FRDGBuilder& GraphBuilder, const FDBufferTextures& DBufferTextures, EShaderPlatform ShaderPlatform)
{
	const FRDGSystemTextures& SystemTextures = FRDGSystemTextures::Get(GraphBuilder);

	FDBufferParameters Parameters;
	Parameters.DBufferATextureSampler = TStaticSamplerState<>::GetRHI();
	Parameters.DBufferBTextureSampler = TStaticSamplerState<>::GetRHI();
	Parameters.DBufferCTextureSampler = TStaticSamplerState<>::GetRHI();
	Parameters.DBufferATexture = SystemTextures.BlackAlphaOne;
	Parameters.DBufferBTexture = SystemTextures.DefaultNormal8Bit;
	Parameters.DBufferCTexture = SystemTextures.BlackAlphaOne;
	Parameters.DBufferRenderMask = SystemTextures.White;

	if (DBufferTextures.IsValid())
	{
		Parameters.DBufferATexture = DBufferTextures.DBufferA;
		Parameters.DBufferBTexture = DBufferTextures.DBufferB;
		Parameters.DBufferCTexture = DBufferTextures.DBufferC;

		if (DBufferTextures.DBufferMask)
		{
			Parameters.DBufferRenderMask = DBufferTextures.DBufferMask;
		}
	}

	return Parameters;
}