Cycles: new Microfacet-based Hair BSDF with elliptical cross-section support #105600

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Weizhen Huang merged 114 commits from weizhen/blender:microfacet_hair into main 2023-08-18 12:46:20 +02:00
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@ -66,7 +66,7 @@ ccl_device int bsdf_microfacet_hair_setup(ccl_private ShaderData *sd,
* the center, to grazing the other edge. This is the sine of the angle
* between sd->Ng and Z, as seen from the tangent X. */
float h = (sd->type & PRIMITIVE_CURVE_RIBBON) ? -sd->v : -dot(X, sd->Ng);
float h = (sd->type & PRIMITIVE_CURVE_RIBBON) ? -sd->v : -dot(X, sd->N);

This is probably fine, but one consideration here is that all functions in the kernel share a namespace, so e.g. sin_theta might easily conflict with something else in the future.
Then again, this is probably general enough that we could just move it to util/ if that happens.

This is probably fine, but one consideration here is that all functions in the kernel share a namespace, so e.g. `sin_theta` might easily conflict with something else in the future. Then again, this is probably general enough that we could just move it to `util/` if that happens.
kernel_assert(fabsf(h) < 1.0f + 1e-4f);
kernel_assert(isfinite_safe(X));
@ -109,6 +109,11 @@ ccl_device_inline float tan_theta(const float3 w)
}
/* Returns sin(phi) and cos(phi) of the given direction. */
ccl_device float sin_phi(const float3 w)
{
return w.x / cos_theta(w);
}
ccl_device float2 sincos_phi(const float3 w)
{
float c = cos_theta(w);
@ -1132,6 +1137,14 @@ ccl_device Spectrum bsdf_microfacet_hair_eval_elliptic(KernelGlobals kg,
const float3 wi = make_float3(dot(sd->I, X), dot(sd->I, Y), dot(sd->I, Z));
const float3 wo = make_float3(dot(omega_in, X), dot(omega_in, Y), dot(omega_in, Z));
/* Treat as transparent material if intersection lies outside of the projected radius. */
const float e2 = 1.0f - sqr(bsdf->extra->eccentricity);
const float radius = sqrtf(1.0f - e2 * sqr(sin_phi(wi)));
if (fabsf(bsdf->extra->geom.w) > radius) {
*pdf = 0.0f;
return zero_spectrum();
}
/* evaluate */
const float3 R = bsdf_microfacet_hair_eval_r_elliptic(sc, wi, wo) +
bsdf_microfacet_hair_eval_tt_trt_elliptic(kg, sc, wi, wo, sd->lcg_state);
@ -1157,12 +1170,6 @@ ccl_device int bsdf_microfacet_hair_sample_elliptic(const KernelGlobals kg,
*eta = bsdf->eta;
const float inv_eta = 1.0f / *eta;
if (bsdf->extra->R <= 0.0f && bsdf->extra->TT <= 0.0f && bsdf->extra->TRT <= 0.0f) {
/* early out for inactive lobe */
*pdf = 0.0f;
return LABEL_NONE;
}
/* get local wi (convention is reversed from other hair bcsdfs) */
const float3 X = float4_to_float3(bsdf->extra->geom);
float3 Y = sd->dPdu;
@ -1171,6 +1178,31 @@ ccl_device int bsdf_microfacet_hair_sample_elliptic(const KernelGlobals kg,
const float3 wi = make_float3(dot(sd->I, X), dot(sd->I, Y), dot(sd->I, Z));
/* get elliptical cross section characteristic */
const float a = 1.0f;
const float b = bsdf->extra->eccentricity;
const float e2 = 1.0f - sqr(b / a);
/* macronormal */
const float2 sincos_phi_i = sincos_phi(wi);
const float sin_phi_i = sincos_phi_i.x;
const float cos_phi_i = sincos_phi_i.y;
const float d_i = sqrtf(1.0f - e2 * sqr(sin_phi_i));
/* Treat as transparent material if intersection lies outside of the projected radius. */
if (fabsf(bsdf->extra->geom.w) > d_i) {
*omega_in = -sd->I;
*pdf = 1;
*eval = one_spectrum();
return LABEL_TRANSMIT | LABEL_TRANSPARENT;
}
if (bsdf->extra->R <= 0.0f && bsdf->extra->TT <= 0.0f && bsdf->extra->TRT <= 0.0f) {
/* early out for inactive lobe */
*pdf = 0.0f;
return LABEL_NONE;
}
const float tilt = -bsdf->alpha;
const float roughness = bsdf->roughness;
const bool beckmann = (bsdf->model_type == NODE_MICROFACET_HAIR_ELLIPTIC_BECKMANN);
@ -1185,16 +1217,6 @@ ccl_device int bsdf_microfacet_hair_sample_elliptic(const KernelGlobals kg,
const float2 sample_h3 = make_float2(lcg_step_float(&sd->lcg_state),
lcg_step_float(&sd->lcg_state));
/* get elliptical cross section characteristic */
const float a = 1.0f;
const float b = bsdf->extra->eccentricity;
const float e2 = 1.0f - sqr(b / a);
/* macronormal */
const float2 sincos_phi_i = sincos_phi(wi);
const float sin_phi_i = sincos_phi_i.x;
const float cos_phi_i = sincos_phi_i.y;
const float d_i = sqrtf(1.0f - e2 * sqr(sin_phi_i));
const float h = d_i * (sample_h * 2.0f - 1.0f);
const float gamma_mi = atan2f(cos_phi_i, -b / a * sin_phi_i) -
acosf(h / sqrtf(sqr(cos_phi_i) + sqr(b / a * sin_phi_i)));