IVSmokeVSMProcessor.h

// Copyright (c) 2026, Team SDB. All rights reserved.
 
#pragma once
 
#include "CoreMinimal.h"
#include "RenderGraphBuilder.h"
#include "RenderGraphResources.h"
 
class FRDGBuilder;
struct FIVSmokeCascadeData;
 
/**
 * Variance Shadow Map processor.
 * Converts depth maps to variance shadow maps and applies blur.
 *
 * VSM stores (depth, depth²) which enables soft shadow filtering
 * without the shadow acne artifacts of PCF.
 */
class IVSMOKE_API FIVSmokeVSMProcessor
{
public:
    FIVSmokeVSMProcessor();
    ~FIVSmokeVSMProcessor();
 
    /**
     * Process a depth texture into a VSM texture.
     * Performs depth → variance conversion and separable Gaussian blur.
     *
     * @param GraphBuilder RDG builder.
     * @param DepthTexture Input depth texture (R32F).
     * @param VSMTexture   Output VSM texture (RG32F).
     * @param BlurRadius   Blur kernel radius (0 = no blur).
     */
    void Process(
        FRDGBuilder& GraphBuilder,
        FRDGTextureRef DepthTexture,
        FRDGTextureRef VSMTexture,
        int32 BlurRadius
    );
 
    /**
     * Process all cascades' depth textures into VSM textures.
     *
     * @param GraphBuilder RDG builder.
     * @param Cascades   Array of cascade data.
     * @param BlurRadius   Blur kernel radius.
     */
    void ProcessCascades(
        FRDGBuilder& GraphBuilder,
        TArray<FIVSmokeCascadeData>& Cascades,
        int32 BlurRadius
    );
 
private:
    /**
     * Convert depth to variance (depth, depth²).
     *
     * @param GraphBuilder RDG builder.
     * @param DepthTexture Input depth texture.
     * @param VSMTexture   Output VSM texture.
     */
    void AddDepthToVariancePass(
        FRDGBuilder& GraphBuilder,
        FRDGTextureRef DepthTexture,
        FRDGTextureRef VSMTexture
    );
 
    /**
     * Apply separable Gaussian blur (horizontal pass).
     *
     * @param GraphBuilder RDG builder.
     * @param SourceTexture Input texture.
     * @param DestTexture   Output texture.
     * @param BlurRadius    Blur kernel radius.
     */
    void AddHorizontalBlurPass(
        FRDGBuilder& GraphBuilder,
        FRDGTextureRef SourceTexture,
        FRDGTextureRef DestTexture,
        int32 BlurRadius
    );
 
    /**
     * Apply separable Gaussian blur (vertical pass).
     *
     * @param GraphBuilder RDG builder.
     * @param SourceTexture Input texture.
     * @param DestTexture   Output texture.
     * @param BlurRadius    Blur kernel radius.
     */
    void AddVerticalBlurPass(
        FRDGBuilder& GraphBuilder,
        FRDGTextureRef SourceTexture,
        FRDGTextureRef DestTexture,
        int32 BlurRadius
    );
};