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Fix Burley BSSRDF NaNs and fireflies.

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Explicitly truncate to Rm same way as the Gaussian BSSRDF, and use safe_sqrtf()
to be sure in case of float precision issues.
This commit is contained in:
Brecht Van Lommel
2016-02-04 23:35:08 +01:00
parent a6ca8a1b73
commit 4443bb8922
2 changed files with 27 additions and 21 deletions
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46
intern/cycles/kernel/closure/bssrdf.h
View File

@@ -65,7 +65,7 @@ ccl_device void bssrdf_gaussian_sample(ShaderClosure *sc, float xi, float *r, fl
*r = sqrtf(r_squared); *r = sqrtf(r_squared);
/* h^2 + r^2 = Rm^2 */ /* h^2 + r^2 = Rm^2 */
*h = sqrtf(Rm*Rm - r_squared); *h = safe_sqrtf(Rm*Rm - r_squared);
} }
/* Planar Cubic BSSRDF falloff /* Planar Cubic BSSRDF falloff
@@ -170,13 +170,20 @@ ccl_device void bssrdf_cubic_sample(ShaderClosure *sc, float xi, float *r, float
*r = r_; *r = r_;
/* h^2 + r^2 = Rm^2 */ /* h^2 + r^2 = Rm^2 */
*h = sqrtf(Rm*Rm - r_*r_); *h = safe_sqrtf(Rm*Rm - r_*r_);
} }
/* Approximate Reflectance Profiles /* Approximate Reflectance Profiles
* http://graphics.pixar.com/library/ApproxBSSRDF/paper.pdf * http://graphics.pixar.com/library/ApproxBSSRDF/paper.pdf
*/ */
/* This is a bit arbitrary, just need big enough radius so it matches
* the mean free length, but still not too big so sampling is still
* effective. Might need some further tweaks.
*/
#define BURLEY_TRUNCATE 10.0f
#define BURLEY_TRUNCATE_CDF 0.973233f // cdf(BURLEY_TRUNCATE)
ccl_device_inline float bssrdf_burley_fitting(float A) ccl_device_inline float bssrdf_burley_fitting(float A)
{ {
/* Diffuse surface transmission, equation (6). */ /* Diffuse surface transmission, equation (6). */
@@ -200,28 +207,33 @@ ccl_device void bssrdf_burley_setup(ShaderClosure *sc)
const float s = bssrdf_burley_fitting(A); const float s = bssrdf_burley_fitting(A);
const float d = l / s; const float d = l / s;
sc->custom1 = l; sc->custom1 = d;
sc->custom2 = s;
sc->custom3 = d;
} }
ccl_device float bssrdf_burley_eval(ShaderClosure *sc, float r) ccl_device float bssrdf_burley_eval(ShaderClosure *sc, float r)
{ {
const float l = sc->custom1, const float d = sc->custom1;
s = sc->custom2; const float Rm = BURLEY_TRUNCATE * d;
if (r >= Rm)
return 0.0f;
/* Clamp to avoid precision issues computing expf(-x)/x */
r = fmaxf(r, 1e-2f * d);
/* Burley refletance profile, equation (3). /* Burley refletance profile, equation (3).
* *
* Note that surface albedo is already included into sc->weight, no need to * Note that surface albedo is already included into sc->weight, no need to
* multiply by this term here. * multiply by this term here.
*/ */
float exp_r_3_d = expf(-s*r / (3.0f * l)); float exp_r_3_d = expf(-r / (3.0f * d));
float exp_r_d = exp_r_3_d * exp_r_3_d * exp_r_3_d; float exp_r_d = exp_r_3_d * exp_r_3_d * exp_r_3_d;
return s * (exp_r_d + exp_r_3_d) / (8*M_PI_F*l*r); return (exp_r_d + exp_r_3_d) / (8*M_PI_F*d*r);
} }
ccl_device float bssrdf_burley_pdf(ShaderClosure *sc, float r) ccl_device float bssrdf_burley_pdf(ShaderClosure *sc, float r)
{ {
return bssrdf_burley_eval(sc, r); return bssrdf_burley_eval(sc, r) * (1.0f/BURLEY_TRUNCATE_CDF);
} }
/* Find the radius for desired CDF value. /* Find the radius for desired CDF value.
@@ -269,18 +281,14 @@ ccl_device void bssrdf_burley_sample(ShaderClosure *sc,
float *r, float *r,
float *h) float *h)
{ {
const float d = sc->custom3; const float d = sc->custom1;
/* This is a bit arbitrary, just need big enough radius so it matches const float Rm = BURLEY_TRUNCATE * d;
* the mean free length, but still not too big so sampling is still const float r_ = bssrdf_burley_root_find(xi * BURLEY_TRUNCATE_CDF) * d;
* effective. Might need some further tweaks.
*/
const float Rm = 10.0f*d;
const float r_ = bssrdf_burley_root_find(xi) * d;
*r = r_; *r = r_;
/* h^2 + r^2 = Rm^2 */ /* h^2 + r^2 = Rm^2 */
*h = sqrtf(Rm*Rm - r_*r_); *h = safe_sqrtf(Rm*Rm - r_*r_);
} }
/* None BSSRDF falloff /* None BSSRDF falloff
@@ -312,7 +320,7 @@ ccl_device void bssrdf_none_sample(ShaderClosure *sc, float xi, float *r, float
*r = r_; *r = r_;
/* h^2 + r^2 = Rm^2 */ /* h^2 + r^2 = Rm^2 */
*h = sqrtf(Rm*Rm - r_*r_); *h = safe_sqrtf(Rm*Rm - r_*r_);
} }
/* Generic */ /* Generic */

2
intern/cycles/kernel/kernel_subsurface.h
View File

@@ -106,8 +106,6 @@ ccl_device float3 subsurface_scatter_eval(ShaderData *sd, ShaderClosure *sc, flo
float sample_weight_inv = 1.0f/sample_weight_sum; float sample_weight_inv = 1.0f/sample_weight_sum;
//printf("num closures %d\n", sd->num_closure);
for(int i = 0; i < sd->num_closure; i++) { for(int i = 0; i < sd->num_closure; i++) {
sc = &sd->closure[i]; sc = &sd->closure[i];