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// Copyright 2009 Intel Corporation
// SPDX-License-Identifier: Apache-2.0
#pragma once
#include "rkcommon/math/math.ih"
OSPRAY_BEGIN_ISPC_NAMESPACE
// input: importance in 'cdf'
// output: cdf of importance in 'cdf'
// return sum
SYCL_EXTERNAL export uniform float Distribution1D_create(
const uniform int size, uniform float *uniform cdf);
struct Sample1D
{
int idx; // relative sample index to start
float frac; // relative prosition of the random sample inside
// the selected bin (useful for random sample re-using)
float pdf; // the pdf of sampling the position idx+frac
// when frac is sampled uniformly inside the idx^th bin
float prob; // the probability of sampling the idx^th bin
};
inline Sample1D Distribution1D_sample(const uniform int size,
const uniform float *uniform cdf,
// we may sample different rows within one gang: use a varying offset
// 'start' instead of a varying pointer 'cdf'
const int start,
const float s)
{
// find minimum index where cdf[i-1] <= s < cdf[i]
int first = start;
int len = size;
while (len > 0) {
const int half = len >> 1;
const int mid = first + half;
if (s < cdf[mid]) {
len = half;
} else {
first = mid + 1;
len -= half + 1;
}
}
Sample1D ret;
ret.idx = first - start;
const float bef = first == start ? 0.0f : cdf[first - 1];
const float dpdf = cdf[first] - bef;
ret.prob = dpdf;
ret.pdf = dpdf * size;
ret.frac = (s - bef) * rcp(dpdf); // rescale
return ret;
}
OSPRAY_END_ISPC_NAMESPACE
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