UE4 shadow: perobjectshadow verification

r.Shadow.PerObject

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PerObjectShadow Include ：

bCreateTranslucentObjectShadow || bCreateInsetObjectShadow || bCreateObjectShadowForStationaryLight

const bool bTranslucentObjectShadow = LightSceneInfo->Proxy->CastsTranslucentShadows() && PrimitiveSceneInfo->Proxy->CastsVolumetricTranslucentShadow();
        const bool bInsetObjectShadow = 
            // Currently only supporting inset shadows on directional lights, but could be made to work with any whole scene shadows
            LightSceneInfo->Proxy->GetLightType() == LightType_Directional
            && PrimitiveSceneInfo->Proxy->CastsInsetShadow();

const uint32 MinShadowResolution     = FMath::Max<int32>(0, CVarMinShadowResolution.GetValueOnRenderThread());
    const uint32 ShadowFadeResolution    = FMath::Max<int32>(0, CVarShadowFadeResolution.GetValueOnRenderThread());

static TAutoConsoleVariable<int32> CVarShadowFadeResolution(
    TEXT("r.Shadow.FadeResolution"),
    64,
    TEXT("Resolution in texels below which shadows are faded out"),
    ECVF_Scalability | ECVF_RenderThreadSafe);

static TAutoConsoleVariable<int32> CVarMinShadowResolution(
    TEXT("r.Shadow.MinResolution"),
    32,
    TEXT("Minimum dimensions (in texels) allowed for rendering shadow subject depths"),
    ECVF_RenderThreadSafe);

AmountShadow, Shadow transparency condition

MinShadowResolution ShadowFadeResolution Shadow fade adjustment , The size can understand the pixel value of the screen .

/**
 * Helper function to determine fade alpha value for shadows based on resolution. In the below ASCII art (1) is
 * the MinShadowResolution and (2) is the ShadowFadeResolution. Alpha will be 0 below the min resolution and 1
 * above the fade resolution. In between it is going to be an exponential curve with the values between (1) and (2)
 * being normalized in the 0..1 range.
 *
 *  
 *  |    /-------
 *  |  /
 *  |/
 *  1-----2-------
 *
 * @param	MaxUnclampedResolution		Requested resolution, unclamped so it can be below min
 * @param	ShadowFadeResolution		Resolution at which fade begins
 * @param	MinShadowResolution			Minimum resolution of shadow
 *
 * @return	fade value between 0 and 1
 */
float CalculateShadowFadeAlpha(const float MaxUnclampedResolution, const uint32 ShadowFadeResolution, const uint32 MinShadowResolution)
{
	// NB: MaxUnclampedResolution < 0 will return FadeAlpha = 0.0f. 

	float FadeAlpha = 0.0f;
	// Shadow size is above fading resolution.
	if (MaxUnclampedResolution > ShadowFadeResolution)
	{
		FadeAlpha = 1.0f;
	}
	// Shadow size is below fading resolution but above min resolution.
	else if (MaxUnclampedResolution > MinShadowResolution)
	{
		const float Exponent = CVarShadowFadeExponent.GetValueOnRenderThread();
		
		// Use the limit case ShadowFadeResolution = MinShadowResolution
		// to gracefully handle this case.
		if (MinShadowResolution >= ShadowFadeResolution)
		{
			const float SizeRatio = (float)(MaxUnclampedResolution - MinShadowResolution);
			FadeAlpha = 1.0f - FMath::Pow(SizeRatio, Exponent);
		} 
		else
		{
			const float InverseRange = 1.0f / (ShadowFadeResolution - MinShadowResolution);
			const float FirstFadeValue = FMath::Pow(InverseRange, Exponent);
			const float SizeRatio = (float)(MaxUnclampedResolution - MinShadowResolution) * InverseRange;
			// Rescale the fade alpha to reduce the change between no fading and the first value, which reduces popping with small ShadowFadeExponent's
			FadeAlpha = (FMath::Pow(SizeRatio, Exponent) - FirstFadeValue) / (1.0f - FirstFadeValue);
		}
	}
	return FadeAlpha;
}

The camera is away from objects , The shadow faded away