-
-
Save skaslev/f82dccb19fd44032b5ba269a8a347424 to your computer and use it in GitHub Desktop.
Ray Tracing Gem's Halton State code, by Electronic Arts, Colin Barré-Brisebois et al. Errata corrected by Alain Galvan.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
// Ray Tracing Gems Chapter 25 | |
// Code provided by Electronic Arts | |
// Colin Barré-Brisebois, Henrik Halén, Graham Wihlidal, Andrew Lauritzen, | |
// Jasper Bekkers, Tomasz Stachowiak, and Johan Andersson | |
// Errata corrected by Alain Galvan | |
struct HaltonState | |
{ | |
unsigned dimension; | |
unsigned sequenceIndex; | |
}; | |
size_t mIncrement = 1; | |
void haltonInit(HaltonState& hState, int x, int y, int path, int numPaths, | |
int frameId, int loop) | |
{ | |
hState.dimension = 2; | |
hState.sequenceIndex = | |
haltonIndex(x, y, (frameId * numPaths + path) % (loop * numPaths)); | |
} | |
float haltonSample(unsigned dimension, unsigned sampleIndex) | |
{ | |
int base = 0; | |
// Use a prime number. | |
switch (dimension) | |
{ | |
case 0: | |
base = 2; | |
break; | |
case 1: | |
base = 3; | |
break; | |
case 2: | |
base = 5; | |
break; | |
case 3: | |
base = 7; | |
break; | |
case 4: | |
base = 11; | |
break; | |
case 5: | |
base = 13; | |
break; | |
case 6: | |
base = 17; | |
break; | |
case 7: | |
base = 19; | |
break; | |
case 8: | |
base = 23; | |
break; | |
case 9: | |
base = 29; | |
break; | |
case 10: | |
base = 31; | |
break; | |
case 11: | |
base = 37; | |
break; | |
case 12: | |
base = 41; | |
break; | |
case 13: | |
base = 43; | |
break; | |
case 14: | |
base = 47; | |
break; | |
case 15: | |
base = 53; | |
break; | |
case 16: | |
base = 59; | |
break; | |
case 17: | |
base = 61; | |
break; | |
case 18: | |
base = 67; | |
break; | |
case 19: | |
base = 71; | |
break; | |
case 20: | |
base = 73; | |
break; | |
case 21: | |
base = 79; | |
break; | |
case 22: | |
base = 83; | |
break; | |
case 23: | |
base = 89; | |
break; | |
case 24: | |
base = 97; | |
break; | |
case 25: | |
base = 101; | |
break; | |
case 26: | |
base = 103; | |
break; | |
case 27: | |
base = 107; | |
break; | |
case 28: | |
base = 109; | |
break; | |
case 29: | |
base = 113; | |
break; | |
case 30: | |
base = 127; | |
break; | |
case 31: | |
base = 131; | |
break; | |
default: | |
base = 2; | |
break; | |
} | |
// Compute the radical inverse. | |
float a = 0; | |
float invBase = 1.0f / float(base); | |
for (float mult = invBase; sampleIndex != 0; | |
sampleIndex /= base, mult *= invBase) | |
{ | |
a += float(sampleIndex % base) * mult; | |
} | |
return a; | |
} | |
float haltonNext(HaltonState& state) | |
{ | |
mIncrement = mIncrement < 1 ? 1 : mIncrement + 1; | |
return haltonSample(state.dimension++, state.sequenceIndex); | |
} | |
// Modified from [pbrt] | |
unsigned halton2Inverse(unsigned index, unsigned digits) | |
{ | |
index = (index << 16) | (index >> 16); | |
index = ((index & 0x00ff00ff) << 8) | ((index & 0xff00ff00) >> 8); | |
index = ((index & 0x0f0f0f0f) << 4) | ((index & 0xf0f0f0f0) >> 4); | |
index = ((index & 0x33333333) << 2) | ((index & 0xcccccccc) >> 2); | |
index = ((index & 0x55555555) << 1) | ((index & 0xaaaaaaaa) >> 1); | |
return index >> (32 - digits); | |
} | |
// Modified from [pbrt] | |
unsigned halton3Inverse(unsigned index, unsigned digits) | |
{ | |
unsigned result = 0; | |
for (unsigned d = 0; d < digits; ++d) | |
{ | |
result = result * 3 + index % 3; | |
index /= 3; | |
} | |
return result; | |
} | |
// Modified from [pbrt] | |
unsigned haltonIndex(unsigned x, unsigned y, unsigned i) | |
{ | |
return ((halton2Inverse(x % 256, 8) * 76545 + | |
halton3Inverse(y % 256, 6) * 110080) % | |
mIncrement) + | |
i * 186624; | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment