Universial render pipeline shadow calc

 https://github.com/Unity-Technologies/Graphics/blob/4ad03e7975af24c8e60c974edb24c696e74e39b3/com.unity.render-pipelines.universal/ShaderLibrary/Shadows.hlsl#L158

https://cyangamedev.wordpress.com/2020/09/22/custom-lighting/

real SampleShadowmapFiltered(TEXTURE2D_SHADOW_PARAM(ShadowMap, sampler_ShadowMap), float4 shadowCoord, ShadowSamplingData samplingData)
	{
	real attenuation;
	#if defined(SHADER_API_MOBILE) || defined(SHADER_API_SWITCH)
	// 4-tap hardware comparison
	real4 attenuation4;
	attenuation4.x = SAMPLE_TEXTURE2D_SHADOW(ShadowMap, sampler_ShadowMap, shadowCoord.xyz + samplingData.shadowOffset0.xyz);
	attenuation4.y = SAMPLE_TEXTURE2D_SHADOW(ShadowMap, sampler_ShadowMap, shadowCoord.xyz + samplingData.shadowOffset1.xyz);
	attenuation4.z = SAMPLE_TEXTURE2D_SHADOW(ShadowMap, sampler_ShadowMap, shadowCoord.xyz + samplingData.shadowOffset2.xyz);
	attenuation4.w = SAMPLE_TEXTURE2D_SHADOW(ShadowMap, sampler_ShadowMap, shadowCoord.xyz + samplingData.shadowOffset3.xyz);
	attenuation = dot(attenuation4, 0.25);
	#else
	float fetchesWeights[9];
	float2 fetchesUV[9];
	SampleShadow_ComputeSamples_Tent_5x5(samplingData.shadowmapSize, shadowCoord.xy, fetchesWeights, fetchesUV);
	attenuation = fetchesWeights[0] * SAMPLE_TEXTURE2D_SHADOW(ShadowMap, sampler_ShadowMap, float3(fetchesUV[0].xy, shadowCoord.z));
	attenuation += fetchesWeights[1] * SAMPLE_TEXTURE2D_SHADOW(ShadowMap, sampler_ShadowMap, float3(fetchesUV[1].xy, shadowCoord.z));
	attenuation += fetchesWeights[2] * SAMPLE_TEXTURE2D_SHADOW(ShadowMap, sampler_ShadowMap, float3(fetchesUV[2].xy, shadowCoord.z));
	attenuation += fetchesWeights[3] * SAMPLE_TEXTURE2D_SHADOW(ShadowMap, sampler_ShadowMap, float3(fetchesUV[3].xy, shadowCoord.z));
	attenuation += fetchesWeights[4] * SAMPLE_TEXTURE2D_SHADOW(ShadowMap, sampler_ShadowMap, float3(fetchesUV[4].xy, shadowCoord.z));
	attenuation += fetchesWeights[5] * SAMPLE_TEXTURE2D_SHADOW(ShadowMap, sampler_ShadowMap, float3(fetchesUV[5].xy, shadowCoord.z));
	attenuation += fetchesWeights[6] * SAMPLE_TEXTURE2D_SHADOW(ShadowMap, sampler_ShadowMap, float3(fetchesUV[6].xy, shadowCoord.z));
	attenuation += fetchesWeights[7] * SAMPLE_TEXTURE2D_SHADOW(ShadowMap, sampler_ShadowMap, float3(fetchesUV[7].xy, shadowCoord.z));
	attenuation += fetchesWeights[8] * SAMPLE_TEXTURE2D_SHADOW(ShadowMap, sampler_ShadowMap, float3(fetchesUV[8].xy, shadowCoord.z));
	#endif
	return attenuation;
	}
	real SampleShadowmap(TEXTURE2D_SHADOW_PARAM(ShadowMap, sampler_ShadowMap), float4 shadowCoord, ShadowSamplingData samplingData, half4 shadowParams, bool isPerspectiveProjection = true)
	{
	// Compiler will optimize this branch away as long as isPerspectiveProjection is known at compile time
	if (isPerspectiveProjection)
	shadowCoord.xyz /= shadowCoord.w;
	real attenuation;
	real shadowStrength = shadowParams.x;
	// TODO: We could branch on if this light has soft shadows (shadowParams.y) to save perf on some platforms.
	#ifdef _SHADOWS_SOFT
	attenuation = SampleShadowmapFiltered(TEXTURE2D_SHADOW_ARGS(ShadowMap, sampler_ShadowMap), shadowCoord, samplingData);
	#else
	// 1-tap hardware comparison
	attenuation = SAMPLE_TEXTURE2D_SHADOW(ShadowMap, sampler_ShadowMap, shadowCoord.xyz);
	#endif
	attenuation = LerpWhiteTo(attenuation, shadowStrength);
	// Shadow coords that fall out of the light frustum volume must always return attenuation 1.0
	// TODO: We could use branch here to save some perf on some platforms.
	return BEYOND_SHADOW_FAR(shadowCoord) ? 1.0 : attenuation;
	}
	half ComputeCascadeIndex(float3 positionWS)
	{
	float3 fromCenter0 = positionWS - _CascadeShadowSplitSpheres0.xyz;
	float3 fromCenter1 = positionWS - _CascadeShadowSplitSpheres1.xyz;
	float3 fromCenter2 = positionWS - _CascadeShadowSplitSpheres2.xyz;
	float3 fromCenter3 = positionWS - _CascadeShadowSplitSpheres3.xyz;
	float4 distances2 = float4(dot(fromCenter0, fromCenter0), dot(fromCenter1, fromCenter1), dot(fromCenter2, fromCenter2), dot(fromCenter3, fromCenter3));
	half4 weights = half4(distances2 < _CascadeShadowSplitSphereRadii);
	weights.yzw = saturate(weights.yzw - weights.xyz);
	return 4 - dot(weights, half4(4, 3, 2, 1));
	}
	float4 TransformWorldToShadowCoord(float3 positionWS)
	{
	#ifdef _MAIN_LIGHT_SHADOWS_CASCADE
	half cascadeIndex = ComputeCascadeIndex(positionWS);
	#else
	half cascadeIndex = 0;
	#endif
	return mul(_MainLightWorldToShadow[cascadeIndex], float4(positionWS, 1.0));
	}
	half MainLightRealtimeShadow(float4 shadowCoord)
	{
	#if !defined(MAIN_LIGHT_CALCULATE_SHADOWS)
	return 1.0h;
	#endif
	ShadowSamplingData shadowSamplingData = GetMainLightShadowSamplingData();
	half4 shadowParams = GetMainLightShadowParams();
	return SampleShadowmap(TEXTURE2D_ARGS(_MainLightShadowmapTexture, sampler_MainLightShadowmapTexture), shadowCoord, shadowSamplingData, shadowParams, false);
	}
	half AdditionalLightRealtimeShadow(int lightIndex, float3 positionWS)
	{
	#if !defined(ADDITIONAL_LIGHT_CALCULATE_SHADOWS)
	return 1.0h;
	#endif
	ShadowSamplingData shadowSamplingData = GetAdditionalLightShadowSamplingData();
	#if USE_STRUCTURED_BUFFER_FOR_LIGHT_DATA
	lightIndex = _AdditionalShadowsIndices[lightIndex];
	// We have to branch here as otherwise we would sample buffer with lightIndex == -1.
	// However this should be ok for platforms that store light in SSBO.