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Cycles: use low-distortion mapping when sampling cone and hemisphere

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based on concentric disk mapping.
Concentric disk mapping was already present, but not used everywhere.
Now `sample_cos_hemisphere()`, `sample_uniform_hemisphere()`, and
`sample_uniform_cone()` use concentric disk mapping.
This changes the noise in many test images.

Pull Request: https://projects.blender.org/blender/blender/pulls/109774
This commit is contained in:
Weizhen Huang
2023-08-23 17:25:27 +02:00
committed by Weizhen Huang
parent 445fabeae9
commit 1284e98ab8
12 changed files with 47 additions and 71 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
intern/cycles/kernel/camera/camera.h
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@@ -20,7 +20,7 @@ ccl_device float2 camera_sample_aperture(ccl_constant KernelCamera *cam, const f
if (blades == 0.0f) {
/* sample disk */
bokeh = concentric_sample_disk(rand);
bokeh = sample_uniform_disk(rand);
}
else {
/* sample polygon */

2
intern/cycles/kernel/closure/bsdf_microfacet.h
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@@ -195,7 +195,7 @@ ccl_device_forceinline float3 microfacet_ggx_sample_vndf(const float3 wi,
}
/* Section 4.2: Parameterization of the projected area. */
float2 t = concentric_sample_disk(rand);
float2 t = sample_uniform_disk(rand);
t.y = mix(safe_sqrtf(1.0f - sqr(t.x)), t.y, 0.5f * (1.0f + wi_.z));
/* Section 4.3: Reprojection onto hemisphere. */

2
intern/cycles/kernel/closure/bsdf_sheen.h
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@@ -82,7 +82,7 @@ ccl_device int bsdf_sheen_sample(ccl_private const ShaderClosure *sc,
const float3 N = bsdf->N, T = bsdf->T, B = bsdf->B;
float a = bsdf->transformA, b = bsdf->transformB;
float2 disk = concentric_sample_disk(rand);
float2 disk = sample_uniform_disk(rand);
float diskZ = safe_sqrtf(1.0f - dot(disk, disk));
float3 localO = normalize(make_float3((disk.x - diskZ * b) / a, disk.y / a, diskZ));

6
intern/cycles/kernel/closure/bsdf_toon.h
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@@ -90,7 +90,8 @@ ccl_device int bsdf_diffuse_toon_sample(ccl_private const ShaderClosure *sc,
float angle = sample_angle * rand.x;
if (sample_angle > 0.0f) {
sample_uniform_cone(bsdf->N, sample_angle, rand, wo, pdf);
float unused;
*wo = sample_uniform_cone(bsdf->N, one_minus_cos(sample_angle), rand, &unused, pdf);
if (dot(Ng, *wo) > 0.0f) {
*eval = make_spectrum(*pdf * bsdf_toon_get_intensity(max_angle, smooth, angle));
@@ -167,7 +168,8 @@ ccl_device int bsdf_glossy_toon_sample(ccl_private const ShaderClosure *sc,
float sample_angle = bsdf_toon_get_sample_angle(max_angle, smooth);
float angle = sample_angle * rand.x;
sample_uniform_cone(R, sample_angle, rand, wo, pdf);
float unused;
*wo = sample_uniform_cone(R, one_minus_cos(sample_angle), rand, &unused, pdf);
if (dot(Ng, *wo) > 0.0f) {
float cosNO = dot(bsdf->N, *wo);

5
intern/cycles/kernel/light/background.h
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@@ -277,11 +277,10 @@ ccl_device_inline float3 background_sun_sample(KernelGlobals kg,
float2 rand,
ccl_private float *pdf)
{
float3 D;
const float3 N = float4_to_float3(kernel_data.background.sun);
const float angle = kernel_data.background.sun.w;
sample_uniform_cone(N, angle, rand, &D, pdf);
return D;
float unused;
return sample_uniform_cone(N, one_minus_cos(angle), rand, &unused, pdf);
}
ccl_device_inline float background_sun_pdf(KernelGlobals kg, float3 D)

2
intern/cycles/kernel/light/common.h
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@@ -31,7 +31,7 @@ typedef struct LightSample {
ccl_device_inline float3 ellipse_sample(float3 ru, float3 rv, float2 rand)
{
const float2 uv = concentric_sample_disk(rand);
const float2 uv = sample_uniform_disk(rand);
return ru * uv.x + rv * uv.y;
}

4
intern/cycles/kernel/light/distant.h
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@@ -36,8 +36,8 @@ ccl_device_inline bool distant_light_sample(const ccl_global KernelLight *klight
ccl_private LightSample *ls)
{
float unused;
sample_uniform_cone_concentric(
klight->co, klight->distant.one_minus_cosangle, rand, &unused, &ls->Ng, &ls->pdf);
ls->Ng = sample_uniform_cone(
klight->co, klight->distant.one_minus_cosangle, rand, &unused, &ls->pdf);
ls->P = ls->Ng;
ls->D = -ls->Ng;

2
intern/cycles/kernel/light/point.h
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@@ -25,7 +25,7 @@ ccl_device_inline bool point_light_sample(const ccl_global KernelLight *klight,
float cos_theta;
if (d_sq > r_sq) {
const float one_minus_cos = sin_sqr_to_one_minus_cos(r_sq / d_sq);
sample_uniform_cone_concentric(-lightN, one_minus_cos, rand, &cos_theta, &ls->D, &ls->pdf);
ls->D = sample_uniform_cone(-lightN, one_minus_cos, rand, &cos_theta, &ls->pdf);
}
else {
const bool has_transmission = (shader_flags & SD_BSDF_HAS_TRANSMISSION);

7
intern/cycles/kernel/light/spot.h
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@@ -61,13 +61,12 @@ ccl_device_inline bool spot_light_sample(const ccl_global KernelLight *klight,
if (in_volume_segment || one_minus_cos_half_angle < one_minus_cos_half_spot_spread) {
/* Sample visible part of the sphere. */
sample_uniform_cone_concentric(
-lightN, one_minus_cos_half_angle, rand, &cos_theta, &ls->D, &ls->pdf);
ls->D = sample_uniform_cone(-lightN, one_minus_cos_half_angle, rand, &cos_theta, &ls->pdf);
}
else {
/* Sample spread cone. */
sample_uniform_cone_concentric(
-klight->spot.dir, one_minus_cos_half_spot_spread, rand, &cos_theta, &ls->D, &ls->pdf);
ls->D = sample_uniform_cone(
-klight->spot.dir, one_minus_cos_half_spot_spread, rand, &cos_theta, &ls->pdf);
if (!ray_sphere_intersect(P, ls->D, 0.0f, FLT_MAX, center, radius, &ls->P, &ls->t)) {
/* Sampled direction does not intersect with the light. */

78
intern/cycles/kernel/sample/mapping.h
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@@ -9,19 +9,9 @@
CCL_NAMESPACE_BEGIN
/* distribute uniform xy on [0,1] over unit disk [-1,1] */
ccl_device void to_unit_disk(ccl_private float2 *rand)
{
float phi = M_2PI_F * rand->x;
float r = sqrtf(rand->y);
rand->x = r * cosf(phi);
rand->y = r * sinf(phi);
}
/* Distribute 2D uniform random samples on [0, 1] over unit disk [-1, 1], with concentric mapping
* to better preserve stratification for some RNG sequences. */
ccl_device float2 concentric_sample_disk(const float2 rand)
ccl_device float2 sample_uniform_disk(const float2 rand)
{
float phi, r;
float a = 2.0f * rand.x - 1.0f;
@@ -55,11 +45,11 @@ ccl_device void make_orthonormals_tangent(const float3 N,
/* sample direction with cosine weighted distributed in hemisphere */
ccl_device_inline void sample_cos_hemisphere(const float3 N,
float2 rand,
float2 rand_in,
ccl_private float3 *wo,
ccl_private float *pdf)
{
to_unit_disk(&rand);
float2 rand = sample_uniform_disk(rand_in);
float costheta = safe_sqrtf(1.0f - len_squared(rand));
float3 T, B;
@@ -80,42 +70,23 @@ ccl_device_inline void sample_uniform_hemisphere(const float3 N,
ccl_private float3 *wo,
ccl_private float *pdf)
{
float z = rand.x;
float r = sin_from_cos(z);
float phi = M_2PI_F * rand.y;
float x = r * cosf(phi);
float y = r * sinf(phi);
float2 xy = sample_uniform_disk(rand);
float z = 1.0f - len_squared(xy);
xy *= safe_sqrtf(z + 1.0f);
float3 T, B;
make_orthonormals(N, &T, &B);
*wo = x * T + y * B + z * N;
*pdf = 0.5f * M_1_PI_F;
}
/* sample direction uniformly distributed in cone */
ccl_device_inline void sample_uniform_cone(
const float3 N, float angle, const float2 rand, ccl_private float3 *wo, ccl_private float *pdf)
{
const float cosThetaMin = cosf(angle);
const float cosTheta = mix(cosThetaMin, 1.0f, rand.x);
const float sinTheta = sin_from_cos(cosTheta);
const float phi = M_2PI_F * rand.y;
const float x = sinTheta * cosf(phi);
const float y = sinTheta * sinf(phi);
const float z = cosTheta;
float3 T, B;
make_orthonormals(N, &T, &B);
*wo = x * T + y * B + z * N;
*pdf = M_1_2PI_F / (1.0f - cosThetaMin);
*wo = xy.x * T + xy.y * B + z * N;
*pdf = M_1_2PI_F;
}
ccl_device_inline float pdf_uniform_cone(const float3 N, float3 D, float angle)
{
float zMin = cosf(angle);
float z = precise_angle(N, D);
if (z < angle) {
return M_1_2PI_F / (1.0f - zMin);
return M_1_2PI_F / one_minus_cos(angle);
}
return 0.0f;
}
@@ -125,12 +96,11 @@ ccl_device_inline float pdf_uniform_cone(const float3 N, float3 D, float angle)
* `cos_theta`.
* Pass `1 - cos(angle)` as argument instead of `angle` to alleviate precision issues at small
* angles (see sphere light for reference). */
ccl_device_inline void sample_uniform_cone_concentric(const float3 N,
const float one_minus_cos_angle,
const float2 rand,
ccl_private float *cos_theta,
ccl_private float3 *wo,
ccl_private float *pdf)
ccl_device_inline float3 sample_uniform_cone(const float3 N,
const float one_minus_cos_angle,
const float2 rand,
ccl_private float *cos_theta,
ccl_private float *pdf)
{
if (one_minus_cos_angle > 0) {
/* Remap radius to get a uniform distribution w.r.t. solid angle on the cone.
@@ -155,7 +125,7 @@ ccl_device_inline void sample_uniform_cone_concentric(const float3 N,
* r_cone: `r_cone(r_disk) = r_cone(rand(r_disk)) = sin_from_cos(mix(cos_angle, 1, r_disk^2))`.
* In practice, we need to replace `rand` with `1 - rand` to preserve the stratification,
* but since it's uniform, that's fine. */
float2 xy = concentric_sample_disk(rand);
float2 xy = sample_uniform_disk(rand);
const float r2 = len_squared(xy);
/* Equivalent to `mix(cos_angle, 1.0f, 1.0f - r2)` */
@@ -164,17 +134,17 @@ ccl_device_inline void sample_uniform_cone_concentric(const float3 N,
/* Remap disk radius to cone radius, equivalent to `xy *= sin_theta / sqrt(r2); */
xy *= safe_sqrtf(one_minus_cos_angle * (2.0f - one_minus_cos_angle * r2));
*pdf = M_1_2PI_F / one_minus_cos_angle;
float3 T, B;
make_orthonormals(N, &T, &B);
return xy.x * T + xy.y * B + *cos_theta * N;
}
*wo = xy.x * T + xy.y * B + *cos_theta * N;
*pdf = M_1_2PI_F / one_minus_cos_angle;
}
else {
*cos_theta = 1.0f;
*wo = N;
*pdf = 1.0f;
}
*cos_theta = 1.0f;
*pdf = 1.0f;
return N;
}
/* sample uniform point on the surface of a sphere */

2
intern/cycles/kernel/svm/ao.h
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@@ -53,7 +53,7 @@ ccl_device float svm_ao(
const float2 rand_disk = path_branched_rng_2D(
kg, &rng_state, sample, num_samples, PRNG_SURFACE_AO);
float2 d = concentric_sample_disk(rand_disk);
float2 d = sample_uniform_disk(rand_disk);
float3 D = make_float3(d.x, d.y, safe_sqrtf(1.0f - dot(d, d)));
/* Create ray. */

6
intern/cycles/util/math.h
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@@ -758,6 +758,12 @@ ccl_device_inline float sin_sqr_to_one_minus_cos(const float s_sq)
return s_sq > 0.0004f ? 1.0f - safe_sqrtf(1.0f - s_sq) : 0.5f * s_sq;
}
ccl_device_inline float one_minus_cos(const float angle)
{
/* Using second-order Taylor expansion at small angles for better accuracy. */
return angle > 0.02f ? 1.0f - cosf(angle) : 0.5f * sqr(angle);
}
ccl_device_inline float pow20(float a)
{
return sqr(sqr(sqr(sqr(a)) * a));