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Calculates AO and the average direction where the ambient light came from.
/*
* Ambient Occlusion and Direction.
*
* Calculates AO and the average direction where the ambient light came from.
*
* Original AO code from https://github.com/sambler/osl-shaders/blob/master/ramps/BaAmbientOcclusion/BaAmbientOcclusion.osl
*
*/
void rng_seed(output int rng, int seed)
{
int chash = seed;
if (chash == 0) chash = 1;
rng = chash * 891694213;
}
float rng_uniform(output int rng)
{
float res = rng / float(2137483647) * 0.5 + 0.5;
rng *= 891694213;
return res;
}
void to_unit_disk(float x, float y, output float x_out, output float y_out)
{
float r, phi;
float a = 2.0 * x - 1.0;
float b = 2.0 * y - 1.0;
if(a > -b) {
if(a > b) {
r = a;
phi = M_PI_4 *(b/a);
}
else {
r = b;
phi = M_PI_4 *(2.0 - a/b);
}
}
else {
if(a < b) {
r = -a;
phi = M_PI_4 *(4.0 + b/a);
}
else {
r = -b;
if(b != 0.0) phi = M_PI_4 *(6.0 - a/b);
else phi = 0.0;
}
}
x_out = r * cos(phi);
y_out = r * sin(phi);
}
void make_orthonormals(vector N, output vector a, output vector b)
{
if(N[0] != N[1] || N[0] != N[2]) a = cross(vector(1, 1, 1), N);
else a = cross(vector(-1, 1, 1), N);
a = normalize(a);
b = cross(N, a);
}
vector sample_cos_hemisphere(vector N, float randu, float randv)
{
vector T, B;
make_orthonormals(N, T, B);
to_unit_disk(randu, randv, randu, randv);
float costheta = sqrt(max(1.0 - randu * randu - randv * randv, 0.0));
return randu * T + randv * B + costheta * N;
}
shader AmbientOcclusionAndDirection(
normal Normal = N,
float Distance = 1,
int Samples = 8,
output float AmbientAmount = 1,
output normal NonOccludedDirection = Normal )
{
int i, rng, hits = 0;
float f, randu, randv, ray_t;
vector ray_P, ray_R;
f = fmod(cellnoise(P*123456.0), 1.0);
rng_seed(rng, int(f * 2137483647));
vector accumulatedNonOccludedNormals = vector(0,0,0);
for(i = 0; i < Samples; i++) {
randu = rng_uniform(rng);
randv = rng_uniform(rng);
ray_R = sample_cos_hemisphere(Normal, randu, randv);
if(trace(P, ray_R, "maxdist", Distance))
{
hits++;
}
else
{
accumulatedNonOccludedNormals += ray_R;
}
}
if(Samples - hits > 0)
{
// ambient light rays found.
// calculate the amount of ambient light and the direction where most of it came from
AmbientAmount = 1.0 - (((float)hits)/Samples);
NonOccludedDirection = normalize(accumulatedNonOccludedNormals);
}
else
{
// every ray has hit some geometry. no ambient light detected.
AmbientAmount = 0.0;
// should the resulting direction be equal to Normal, or zero???
// NonOccludedDirection = vector(0,0,0);
}
}
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