/// <summary>
/// Performs a VPT in a sphere medium with specific settings starting at center and returns the summary of the path traced.
/// </summary>
public static PathSummary GetVPTSampleInSphereOffcenter(MediumSettings settings, GRandom rnd)
{
float3 x = float3(0, 0, 0);
float3 w = float3(0, 0, 1);
float3 X = x;
float3 W = w;
int N = 0;
float accum = 0;
float importance = 1;
// First flight from center
float t = settings.Sigma < 0.00001 ? 10000000 : -log(max(0.000000001f, 1 - rnd.random())) / settings.Sigma;
if (t >= 1.0f) // leaves the sphere before scattering
{
return(new PathSummary
{
N = N,
x = w,
w = w,
X = x, // can not used but in any case...
W = W
});
}
x += w * t; // move to first scatter offcenter
while (true)
{
importance *= settings.Phi;
accum += importance;
if (rnd.random() < importance / accum) // replace the representative by this one
{
X = x;
W = w;
}
w = SamplePhase(w, settings.G, rnd);
N++;
float d = DistanceToBoundary(x, w);
t = settings.Sigma < 0.00001 ? 10000000 : -log(max(0.000000001f, 1 - rnd.random())) / settings.Sigma;
if (t >= d || float.IsNaN(t) || float.IsInfinity(t))
{
x += w * d;
return(new PathSummary
{
N = N,
x = x,
w = w,
X = X,
W = W
});
}
x += w * t;
}
}
/// <summary>
/// Performs a VPT in a sphere medium with specific settings starting at center and returns the summary of the path traced.
/// </summary>
static PathSummary GetVPTSampleInSphere(MediumSettings settings)
{
float3 x = float3(0, 0, 0);
float3 w = float3(0, 0, 1);
float3 X = x;
float3 W = w;
int N = 0;
float accum = 0;
float importance = 1;
while (true)
{
importance *= settings.Phi;
accum += importance;
if (random() < importance / accum) // replace the representative by this one
{
X = x;
W = w;
}
w = SamplePhase(w, settings.G);
N++;
float d = DistanceToBoundary(x, w);
float t = settings.Sigma < 0.00001 ? 10000000 : -log(max(0.000000001f, 1 - random())) / settings.Sigma;
if (t >= d || float.IsNaN(t) || float.IsInfinity(t))
{
x += w * d;
return(new PathSummary
{
N = N,
x = x,
w = w,
X = X,
W = W
});
}
x += w * t;
}
}
static void GenerateDatasetForTabulationMethod()
{
/*
* This method generates data samples and builds a table using
* the idea in Mueller et al 2016.
*/
float[] table = new float[BINS_G * BINS_SA * BINS_R * BINS_THETA];
float[,,] oneTimeScatteringAlbedo = new float[BINS_G, BINS_SA, BINS_R];
float[,,] multiTimeScatteringAlbedo = new float[BINS_G, BINS_SA, BINS_R];
int MAX_N = 200;
int P = 1 << 18; // one quarter million photons per setting.
Console.WriteLine("Process started.");
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
int TOTAL_NUMBER_OF_SETTINGS = BINS_G * BINS_R;
int solvedSettings = 0;
Parallel.For(0, BINS_G, binG =>
{
GRandom rnd = new GRandom(binG);
float g = (binG + rnd.random()) * 2.0f * 0.99f / BINS_G - 0.99f;
for (int binR = 0; binR < BINS_R; binR++)
{
float r = pow(2.0f, binR);
Console.WriteLine("Solved {0}%.", solvedSettings * 100.0f / TOTAL_NUMBER_OF_SETTINGS);
if (solvedSettings >= 1)
{
Console.WriteLine("ETA {0} ", stopwatch.Elapsed * (TOTAL_NUMBER_OF_SETTINGS / (float)solvedSettings - 1));
}
MediumSettings settings = new MediumSettings();
settings.Sigma = r;
settings.Phi = 1;
settings.G = g;
long[,] Hl = new long[BINS_THETA, MAX_N + 1];
for (int sample = 0; sample < P; sample++)
{
var summary = Scattering.GetVPTSampleInSphereOffcenter(settings, rnd);
int thetaBin = (int)min(BINS_THETA - 1, BINS_THETA * (summary.x.z * 0.5f + 0.5f));
int nBin = (int)min(MAX_N, summary.N);
Hl[thetaBin, nBin]++;
}
for (int binSA = 0; binSA < BINS_SA; binSA++)
{
float phi = binSA == BINS_SA - 1 ? 1.0f : 1 - exp(binSA * log(0.001f) / (BINS_SA - 1));
for (int binTheta = 0; binTheta < BINS_THETA; binTheta++)
{
int pos = STRIDE_G * binG + STRIDE_SA * binSA + STRIDE_R * binR + binTheta;
for (int n = 2; n <= MAX_N; n++)
{
table[pos] += pow(phi, n) * Hl[binTheta, n];
multiTimeScatteringAlbedo[binG, binSA, binR] += pow(phi, n) * Hl[binTheta, n];
}
oneTimeScatteringAlbedo[binG, binSA, binR] += phi * Hl[binTheta, 1];
}
// Sum and normalize table slice to create an empirical cdf
for (int binTheta = 0; binTheta < BINS_THETA; binTheta++)
{
int pos = STRIDE_G * binG + STRIDE_SA * binSA + STRIDE_R * binR + binTheta;
if (binTheta > 0)
{
table[pos] += table[pos - 1];
}
}
}
solvedSettings++;
}
});
Console.WriteLine("Finished generation in {0}", stopwatch.Elapsed);
Console.WriteLine("Saving table");
BinaryWriter bw = new BinaryWriter(new FileStream("stf.bin", FileMode.Create));
for (int binG = 0; binG < BINS_G; binG++)
{
for (int binSA = 0; binSA < BINS_SA; binSA++)
{
for (int binR = 0; binR < BINS_R; binR++)
{
bw.Write(oneTimeScatteringAlbedo[binG, binSA, binR] / P);
}
}
}
for (int binG = 0; binG < BINS_G; binG++)
{
for (int binSA = 0; binSA < BINS_SA; binSA++)
{
for (int binR = 0; binR < BINS_R; binR++)
{
bw.Write(multiTimeScatteringAlbedo[binG, binSA, binR] / P);
}
}
}
int index = 0;
for (int binG = 0; binG < BINS_G; binG++)
{
for (int binSA = 0; binSA < BINS_SA; binSA++)
{
for (int binR = 0; binR < BINS_R; binR++)
{
for (int binTheta = 0; binTheta < BINS_THETA; binTheta++)
{
bw.Write(table[index++] / P);
}
}
}
}
bw.Close();
Console.WriteLine("Done.");
}