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346 行
16 KiB
346 行
16 KiB
using System;
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using UnityEngine.Rendering;
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namespace UnityEngine.Experimental.Rendering.LightweightPipeline
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{
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//A minimal implementation of HDRP Diffusion Profile, to support out preintegrated subsurface scattering model.
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[GenerateHLSL]
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public class DiffusionProfileConstants
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{
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public const int DIFFUSION_PROFILE_COUNT = 5;
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public const int DIFFUSION_PROFILE_NEUTRAL_ID = 0;
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public const int SSS_N_SAMPLES = 11;
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public const int SSS_DISTANCE_SCALE = 3;
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}
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public static class DiffusionProfileShaderIDs
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{
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public static readonly int _StdDev1 = Shader.PropertyToID("_StdDev1");
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public static readonly int _StdDev2 = Shader.PropertyToID("_StdDev2");
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public static readonly int _LerpWeight = Shader.PropertyToID("_LerpWeight");
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public static readonly int _HalfRcpVarianceAndWeight1 = Shader.PropertyToID("_HalfRcpVarianceAndWeight1");
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public static readonly int _HalfRcpVarianceAndWeight2 = Shader.PropertyToID("_HalfRcpVarianceAndWeight2");
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public static readonly int _TransmissionTint = Shader.PropertyToID("_TransmissionTint");
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public static readonly int _ThicknessRemap = Shader.PropertyToID("_ThicknessRemap");
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//Addition Runtime Constants
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public static readonly int _PreintegratedDiffuseScatteringTextures = Shader.PropertyToID("_PreintegratedDiffuseScatteringTextures");
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public static readonly int _HalfRcpVariancesAndWeights = Shader.PropertyToID("_HalfRcpVariancesAndWeights");
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}
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[Serializable]
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public sealed class DiffusionProfile
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{
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public string name;
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[ColorUsage(false, true)] public Color scatterDistance1;
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[ColorUsage(false, true)] public Color scatterDistance2;
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[Range(0f, 1f)] public float lerpWeight;
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[ColorUsage(false)] public Color transmissionTint;
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public Vector2 thicknessRemap;
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public Vector4[] filterKernel { get; private set; }
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public Vector4 halfRcpWeightedVariances { get; private set; }
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public DiffusionProfile(string name)
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{
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this.name = name;
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scatterDistance1 = new Color(0.3f, 0.3f, 0.3f, 0f);
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scatterDistance2 = new Color(0.5f, 0.5f, 0.5f, 0f);
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lerpWeight = 1f;
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transmissionTint = Color.white;
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thicknessRemap = new Vector2(0f, 5f);
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}
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public void Validate()
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{
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thicknessRemap.y = Mathf.Max(thicknessRemap.y, 0f);
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thicknessRemap.x = Mathf.Clamp(thicknessRemap.x, 0f, thicknessRemap.y);
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scatterDistance1 = new Color
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{
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r = Mathf.Max(0.05f, scatterDistance1.r),
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g = Mathf.Max(0.05f, scatterDistance1.g),
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b = Mathf.Max(0.05f, scatterDistance1.b),
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a = 0.0f
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};
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scatterDistance2 = new Color
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{
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r = Mathf.Max(0.05f, scatterDistance2.r),
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g = Mathf.Max(0.05f, scatterDistance2.g),
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b = Mathf.Max(0.05f, scatterDistance2.b),
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a = 0.0f
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};
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UpdateKernelAndVarianceData();
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}
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public void UpdateKernelAndVarianceData()
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{
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const int kNumSamples = DiffusionProfileConstants.SSS_N_SAMPLES;
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const int kDistanceScale = DiffusionProfileConstants.SSS_DISTANCE_SCALE;
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if (filterKernel == null || filterKernel.Length != kNumSamples)
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filterKernel = new Vector4[kNumSamples];
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// Apply the three-sigma rule, and rescale.
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var stdDev1 = ((1f / 3f) * kDistanceScale) * scatterDistance1;
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var stdDev2 = ((1f / 3f) * kDistanceScale) * scatterDistance2;
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// Our goal is to blur the image using a filter which is represented
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// as a product of a linear combination of two normalized 1D Gaussians
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// as suggested by Jimenez et al. in "Separable Subsurface Scattering".
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// A normalized (i.e. energy-preserving) 1D Gaussian with the mean of 0
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// is defined as follows: G1(x, v) = exp(-x * x / (2 * v)) / sqrt(2 * Pi * v),
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// where 'v' is variance and 'x' is the radial distance from the origin.
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// Using the weight 'w', our 1D and the resulting 2D filters are given as:
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// A1(v1, v2, w, x) = G1(x, v1) * (1 - w) + G1(r, v2) * w,
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// A2(v1, v2, w, x, y) = A1(v1, v2, w, x) * A1(v1, v2, w, y).
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// The resulting filter function is a non-Gaussian PDF.
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// It is separable by design, but generally not radially symmetric.
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// N.b.: our scattering distance is rather limited. Therefore, in order to allow
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// for a greater range of standard deviation values for flatter profiles,
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// we rescale the world using 'distanceScale', effectively reducing the SSS
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// distance units from centimeters to (1 / distanceScale).
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// Find the widest Gaussian across 3 color channels.
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float maxStdDev1 = Mathf.Max(stdDev1.r, stdDev1.g, stdDev1.b);
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float maxStdDev2 = Mathf.Max(stdDev2.r, stdDev2.g, stdDev2.b);
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var weightSum = Vector3.zero;
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float step = 1f / (kNumSamples - 1);
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// Importance sample the linear combination of two Gaussians.
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for (int i = 0; i < kNumSamples; i++)
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{
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// Generate 'u' on (0, 0.5] and (0.5, 1).
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float u = (i <= kNumSamples / 2) ? 0.5f - i * step // The center and to the left
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: i * step; // From the center to the right
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u = Mathf.Clamp(u, 0.001f, 0.999f);
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float pos = GaussianCombinationCdfInverse(u, maxStdDev1, maxStdDev2, lerpWeight);
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float pdf = GaussianCombination(pos, maxStdDev1, maxStdDev2, lerpWeight);
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Vector3 val;
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val.x = GaussianCombination(pos, stdDev1.r, stdDev2.r, lerpWeight);
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val.y = GaussianCombination(pos, stdDev1.g, stdDev2.g, lerpWeight);
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val.z = GaussianCombination(pos, stdDev1.b, stdDev2.b, lerpWeight);
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// We do not divide by 'numSamples' since we will renormalize, anyway.
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filterKernel[i].x = val.x * (1 / pdf);
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filterKernel[i].y = val.y * (1 / pdf);
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filterKernel[i].z = val.z * (1 / pdf);
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filterKernel[i].w = pos;
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weightSum.x += filterKernel[i].x;
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weightSum.y += filterKernel[i].y;
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weightSum.z += filterKernel[i].z;
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}
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// Renormalize the weights to conserve energy.
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for (int i = 0; i < kNumSamples; i++)
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{
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filterKernel[i].x *= 1 / weightSum.x;
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filterKernel[i].y *= 1 / weightSum.y;
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filterKernel[i].z *= 1 / weightSum.z;
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}
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Vector4 weightedStdDev;
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weightedStdDev.x = Mathf.Lerp(stdDev1.r, stdDev2.r, lerpWeight);
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weightedStdDev.y = Mathf.Lerp(stdDev1.g, stdDev2.g, lerpWeight);
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weightedStdDev.z = Mathf.Lerp(stdDev1.b, stdDev2.b, lerpWeight);
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weightedStdDev.w = Mathf.Lerp(maxStdDev1, maxStdDev2, lerpWeight);
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// Store (1 / (2 * WeightedVariance)) per color channel.
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// Warning: do not use halfRcpWeightedVariances.Set(). It will not work.
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halfRcpWeightedVariances = new Vector4(0.5f / (weightedStdDev.x * weightedStdDev.x),
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0.5f / (weightedStdDev.y * weightedStdDev.y),
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0.5f / (weightedStdDev.z * weightedStdDev.z),
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0.5f / (weightedStdDev.w * weightedStdDev.w));
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}
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static float Gaussian(float x, float stdDev)
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{
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float variance = stdDev * stdDev;
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return Mathf.Exp(-x * x / (2 * variance)) / Mathf.Sqrt(2 * Mathf.PI * variance);
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}
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static float GaussianCombination(float x, float stdDev1, float stdDev2, float lerpWeight)
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{
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return Mathf.Lerp(Gaussian(x, stdDev1), Gaussian(x, stdDev2), lerpWeight);
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}
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static float RationalApproximation(float t)
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{
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// Abramowitz and Stegun formula 26.2.23.
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// The absolute value of the error should be less than 4.5 e-4.
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float[] c = { 2.515517f, 0.802853f, 0.010328f };
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float[] d = { 1.432788f, 0.189269f, 0.001308f };
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return t - ((c[2] * t + c[1]) * t + c[0]) / (((d[2] * t + d[1]) * t + d[0]) * t + 1.0f);
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}
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// Ref: https://www.johndcook.com/blog/csharp_phi_inverse/
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static float NormalCdfInverse(float p, float stdDev)
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{
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float x;
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if (p < 0.5)
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{
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// F^-1(p) = - G^-1(p)
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x = -RationalApproximation(Mathf.Sqrt(-2f * Mathf.Log(p)));
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}
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else
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{
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// F^-1(p) = G^-1(1-p)
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x = RationalApproximation(Mathf.Sqrt(-2f * Mathf.Log(1f - p)));
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}
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return x * stdDev;
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}
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static float GaussianCombinationCdfInverse(float p, float stdDev1, float stdDev2, float lerpWeight)
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{
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return Mathf.Lerp(NormalCdfInverse(p, stdDev1), NormalCdfInverse(p, stdDev2), lerpWeight);
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}
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}
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public sealed class DiffusionProfileSettings : ScriptableObject
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{
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public DiffusionProfile[] profiles;
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[NonSerialized] public Vector4[] worldScales;
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[NonSerialized] public Vector4[] thicknessRemaps;
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[NonSerialized] public Vector4[] transmissionTints;
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//TODO: Preintegration turns this into a texture
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[NonSerialized] public Vector4[] halfRcpWeightedVariances;
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[NonSerialized] public Vector4[] halfRcpVariancesAndWeights;
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[NonSerialized] public Vector4[] filterKernels;
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[NonSerialized] private Material preintegration;
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[NonSerialized] public TextureCache2D preintegratedScatterLUTs;
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public DiffusionProfile this[int index]
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{
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get
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{
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if (index >= DiffusionProfileConstants.DIFFUSION_PROFILE_COUNT - 1)
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throw new IndexOutOfRangeException("index");
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return profiles[index];
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}
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}
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static void ValidateArray<T>(ref T[] array, int len)
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{
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if (array == null || array.Length != len)
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array = new T[len];
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}
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void OnEnable()
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{
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// The neutral profile is not a part of the array.
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int profileArraySize = DiffusionProfileConstants.DIFFUSION_PROFILE_COUNT - 1;
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if (profiles != null && profiles.Length != profileArraySize)
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Array.Resize(ref profiles, profileArraySize);
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if (profiles == null)
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profiles = new DiffusionProfile[profileArraySize];
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for (int i = 0; i < profileArraySize; i++)
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{
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if (profiles[i] == null)
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profiles[i] = new DiffusionProfile("Profile " + (i + 1));
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profiles[i].Validate();
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}
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ValidateArray(ref thicknessRemaps, DiffusionProfileConstants.DIFFUSION_PROFILE_COUNT);
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ValidateArray(ref worldScales, DiffusionProfileConstants.DIFFUSION_PROFILE_COUNT);
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ValidateArray(ref transmissionTints, DiffusionProfileConstants.DIFFUSION_PROFILE_COUNT);
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ValidateArray(ref halfRcpWeightedVariances, DiffusionProfileConstants.DIFFUSION_PROFILE_COUNT);
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ValidateArray(ref halfRcpVariancesAndWeights, DiffusionProfileConstants.DIFFUSION_PROFILE_COUNT * 2);
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ValidateArray(ref filterKernels, DiffusionProfileConstants.DIFFUSION_PROFILE_COUNT * DiffusionProfileConstants.SSS_N_SAMPLES);
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Debug.Assert(DiffusionProfileConstants.DIFFUSION_PROFILE_NEUTRAL_ID <= 32, "Transmission and Texture flags (32-bit integer) cannot support more than 32 profiles.");
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//NOTE: We can't get reference to the render pipeline assets from scriptable object, but we add it to the assets anyways so they get included in build.
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// Searching here is safe because we linked already in the LW resources, forcing it to be included in build.
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preintegration = CoreUtils.CreateEngineMaterial("Hidden/LightweightPipeline/PreintegratedScatter");
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preintegratedScatterLUTs = new TextureCache2D();
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preintegratedScatterLUTs.AllocTextureArray(DiffusionProfileConstants.DIFFUSION_PROFILE_COUNT, 128, 128, TextureFormat.ARGB32, false);
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UpdateCache();
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}
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public void UpdateCache()
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{
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for (int i = 0; i < DiffusionProfileConstants.DIFFUSION_PROFILE_COUNT - 1; i++)
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{
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UpdateCache(i);
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}
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// Fill the neutral profile.
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int neutralId = DiffusionProfileConstants.DIFFUSION_PROFILE_NEUTRAL_ID;
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halfRcpWeightedVariances[neutralId] = Vector4.one;
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for (int j = 0, n = DiffusionProfileConstants.SSS_N_SAMPLES; j < n; j++)
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{
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filterKernels[n * neutralId + j] = Vector4.one;
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filterKernels[n * neutralId + j].w = 0f;
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}
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}
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public void UpdateCache(int p)
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{
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// 'p' is the profile array index. 'i' is the index in the shader (accounting for the neutral profile).
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int i = p + 1;
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// Erase previous value (This need to be done here individually as in the SSS editor we edit individual component)
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thicknessRemaps[i] = new Vector4(profiles[p].thicknessRemap.x, profiles[p].thicknessRemap.y - profiles[p].thicknessRemap.x, 0f, 0f);
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// Convert ior to fresnel0
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transmissionTints[i] = new Vector4(profiles[p].transmissionTint.r * 0.25f, profiles[p].transmissionTint.g * 0.25f, profiles[p].transmissionTint.b * 0.25f, 0f); // Premultiplied
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//disabledTransmissionTintsAndFresnel0[i] = new Vector4(0.0f, 0.0f, 0.0f, fresnel0);
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halfRcpWeightedVariances[i] = profiles[p].halfRcpWeightedVariances;
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var stdDev1 = ((1f / 3f) * DiffusionProfileConstants.SSS_DISTANCE_SCALE) * (Vector4)profiles[p].scatterDistance1;
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var stdDev2 = ((1f / 3f) * DiffusionProfileConstants.SSS_DISTANCE_SCALE) * (Vector4)profiles[p].scatterDistance2;
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// Multiply by 0.1 to convert from millimeters to centimeters. Apply the distance scale.
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// Rescale by 4 to counter rescaling of transmission tints.
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float a = 0.1f * DiffusionProfileConstants.SSS_DISTANCE_SCALE;
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halfRcpVariancesAndWeights[2 * i + 0] = new Vector4(a * a * 0.5f / (stdDev1.x * stdDev1.x), a * a * 0.5f / (stdDev1.y * stdDev1.y), a * a * 0.5f / (stdDev1.z * stdDev1.z), 4f * (1f - profiles[p].lerpWeight));
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halfRcpVariancesAndWeights[2 * i + 1] = new Vector4(a * a * 0.5f / (stdDev2.x * stdDev2.x), a * a * 0.5f / (stdDev2.y * stdDev2.y), a * a * 0.5f / (stdDev2.z * stdDev2.z), 4f * profiles[p].lerpWeight);
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for (int j = 0, n = DiffusionProfileConstants.SSS_N_SAMPLES; j < n; j++)
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{
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filterKernels[n * i + j] = profiles[p].filterKernel[j];
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}
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RTHandle preintegratedScatterRT = RTHandle.Alloc(128, 128, 1, DepthBits.None, RenderTextureFormat.ARGB32, FilterMode.Point, TextureWrapMode.Clamp, TextureDimension.Tex2D, false);
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preintegration.SetVector(DiffusionProfileShaderIDs._StdDev1, stdDev1);
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preintegration.SetVector(DiffusionProfileShaderIDs._StdDev2, stdDev2);
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preintegration.SetFloat (DiffusionProfileShaderIDs._LerpWeight, profiles[p].lerpWeight);
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CommandBuffer cmd = new CommandBuffer() { name = "BuildLUT_" + p };
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cmd.Blit(null, preintegratedScatterRT, preintegration);
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preintegratedScatterLUTs.TransferToSlice(cmd, i, preintegratedScatterRT);
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Graphics.ExecuteCommandBuffer(cmd);
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}
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}
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}
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