Misaki/SimpleRayTracing
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Fixed genergy conservation problem in specular lobe

Browse Source
This commit is contained in:
Misaki
2025-12-31 03:12:29 +09:00
parent 84b2504a6f
commit 5c988108ef
5 changed files with 228 additions and 86 deletions
Download Patch File Download Diff File Expand all files Collapse all files

74
native/source/Material/StandardLit.c
View File

@@ -27,12 +27,12 @@ static float oren_nayar_eval(vec3s l, vec3s v, vec3s n, float roughness, float n
if (n_dot_v > n_dot_l)
{
sin_alpha = sin_theta_l;
tan_beta = sin_theta_v / fmaxf(n_dot_v, 0.0001f);
tan_beta = sin_theta_v / fmaxf(n_dot_v, FLT_EPSILON);
}
else
{
sin_alpha = sin_theta_v;
tan_beta = sin_theta_l / fmaxf(n_dot_l, 0.0001f);
tan_beta = sin_theta_l / fmaxf(n_dot_l, FLT_EPSILON);
}
return (A + B * cos_phi_diff * sin_alpha * tan_beta) * INV_PI;
@@ -117,19 +117,20 @@ static vec3s evaluate_bsdf_standard_lit(const shading_context_t* context, standa
// Specular (GGX)
float D = ggx_distribution(n_dot_h, surface_data->roughness);
float G = ggx_g_smith(n_dot_v, n_dot_l, surface_data->roughness);
vec3s spec = glms_vec3_scale(glms_vec3_mul(F, (vec3s){D * G, D * G, D * G}), 1.0f / fmaxf(4.0f * n_dot_v * n_dot_l, 0.0001f));
vec3s spec = glms_vec3_scale(glms_vec3_mul(F, (vec3s){D * G, D * G, D * G}),
1.0f / fmaxf(4.0f * n_dot_v * n_dot_l, FLT_EPSILON));
// Multi-scatter GGX (broad lobe)
vec3s ms = ggx_multi_scatter_lambert(f0, n_dot_v, n_dot_l, surface_data->roughness);
// Diffuse (Oren-Nayar)
// Using (1 - F) here can make rough dielectrics look too dark because our specular is single-scatter GGX
// (missing multi-scattering energy compensation). A stable approximation is (1 - F0_diel).
float kd_scale = (1.0f - surface_data->metallic) * (1.0f - DIELECTRIC_REFLECTIVE_F0);
vec3s kD = glms_vec3_scale(glms_vec3_one(), kd_scale);
vec3s kD = glms_vec3_sub(glms_vec3_one(), F);
kD = glms_vec3_scale(kD, (1.0f - surface_data->metallic));
float on_val = oren_nayar_eval(l, v, n, surface_data->diffuse_roughness, n_dot_l, n_dot_v);
vec3s diff = glms_vec3_scale(glms_vec3_mul(surface_data->albedo, kD), on_val);
// return (vec3s){n_dot_h, n_dot_h, n_dot_h};
return glms_vec3_add(glms_vec3_add(diff, spec), ms);
}
@@ -144,7 +145,7 @@ static float sample_bsdf_pdf(const standard_lit_surface_data_t* surface_data, ve
// Lobe probabilities (single-scatter spec vs cosine)
// We allocate some cosine probability for multi-scatter spec, especially for rough metals.
vec3s f0 = glms_vec3_lerp(DIELECTRIC_F0, surface_data->albedo, surface_data->metallic);
float n_dot_v = fmaxf(glms_vec3_dot(surface_data->normal, V), 0.0001f);
float n_dot_v = fmaxf(glms_vec3_dot(surface_data->normal, V), 0.0f);
vec3s F_est = fresnel_schlick_vec3(f0, n_dot_v);
float spec_strength = luminance(F_est);
@@ -159,6 +160,7 @@ static float sample_bsdf_pdf(const standard_lit_surface_data_t* surface_data, ve
{
return 0.0f;
}
w_ss /= sum_w;
w_cos /= sum_w;
@@ -168,16 +170,17 @@ static float sample_bsdf_pdf(const standard_lit_surface_data_t* surface_data, ve
// p_w(wi) = p_h(h) / (4 * (V·H))
vec3s H = glms_vec3_normalize(glms_vec3_add(L, V));
float v_dot_h = glms_vec3_dot(V, H);
if (v_dot_h <= 1e-6f)
if (v_dot_h <= FLT_EPSILON)
{
return 0.0f;
}
float n_dot_h = fmaxf(glms_vec3_dot(surface_data->normal, H), 0.0f);
float D = ggx_distribution(n_dot_h, surface_data->roughness);
float G1v = ggx_g1(n_dot_v, surface_data->roughness);
float pdf_h = (D * G1v * n_dot_h) / fmaxf(n_dot_v, 1e-6f);
float pdf_spec = pdf_h / (4.0f * fmaxf(v_dot_h, 1e-6f));
float pdf_h = (D * G1v * v_dot_h) / fmaxf(n_dot_v, FLT_EPSILON);
float pdf_spec = pdf_h / (4.0f * fmaxf(v_dot_h, FLT_EPSILON));
// Cosine PDF (used for diffuse + multi-scatter)
float pdf_cos = n_dot_l * INV_PI;
@@ -210,7 +213,7 @@ path_output standard_lit_render_loop(const standard_lit_properties_t* properties
surface_data.normal = context->normal;
}
float n_dot_v = fmaxf(glms_vec3_dot(surface_data.normal, V), 0.0001f);
float n_dot_v = fmaxf(glms_vec3_dot(surface_data.normal, V), 0.0f);
// Ensure LUT is ready (thread-safe, one-time).
ggx_ms_init_lut_once();
@@ -284,7 +287,7 @@ path_output standard_lit_render_loop(const standard_lit_properties_t* properties
vec3s f_eval = glms_vec3_zero();
float n_dot_l = 0.0f;
float r_lobe = sobol_sample_scrambled(context->sample_index, sobol_get_dimension(context->bounce_depth, PRNG_BSDF), scramble);
float r_lobe = sobol_sample(context->sample_index, sobol_get_dimension(context->bounce_depth, PRNG_BSDF));
bool is_specular = (r_lobe < w_ss);
if (is_specular)
@@ -297,7 +300,7 @@ path_output standard_lit_render_loop(const standard_lit_properties_t* properties
float u2 = sobol_sample_scrambled(context->sample_index, d2, scramble);
vec3s H = ggx_sample_vndf(surface_data.normal, V, surface_data.roughness, u1, u2);
output.wi = glms_vec3_reflect(context->wo, H); // reflect(-V, H) -> V is wo inverted
output.wi = glms_vec3_reflect(context->wo, H);
if (glms_vec3_dot(output.wi, surface_data.normal) <= 0.0f || glms_vec3_dot(output.wi, context->normal) <= 0.0f)
{
@@ -305,62 +308,35 @@ path_output standard_lit_render_loop(const standard_lit_properties_t* properties
return output;
}
// Recalculate dots
n_dot_l = fmaxf(glms_vec3_dot(surface_data.normal, output.wi), 0.0001f);
vec3s H_new = glms_vec3_normalize(glms_vec3_add(output.wi, V));
float n_dot_h = fmaxf(glms_vec3_dot(surface_data.normal, H_new), 0.0001f);
float v_dot_h = fmaxf(glms_vec3_dot(V, H_new), 0.0001f);
n_dot_l = fmaxf(glms_vec3_dot(surface_data.normal, output.wi), FLT_EPSILON);
// Evaluate BSDF
float D = ggx_distribution(n_dot_h, surface_data.roughness);
float G1v = ggx_g1(n_dot_v, surface_data.roughness);
float G = ggx_g_smith(n_dot_v, n_dot_l, surface_data.roughness);
vec3s f0 = glms_vec3_lerp(DIELECTRIC_F0, surface_data.albedo, surface_data.metallic);
vec3s F = fresnel_schlick_vec3(f0, v_dot_h);
vec3s spec_f = glms_vec3_scale(glms_vec3_mul(F, (vec3s){D * G, D * G, D * G}),
1.0f / fmaxf(4.0f * n_dot_v * n_dot_l, 1e-6f));
f_eval = spec_f;
// Propagate spread angle for ray cones
// Heuristic: spread increases with roughness
// Spread angle heuristic
output.spread_angle = context->spread_angle + surface_data.roughness * QUARTER_PI;
}
else
{
// Sample Cosine hemisphere (Diffuse + Multi-scatter spec)
// Note: We use cosine sampling for Oren-Nayar and the broad MS term.
uint32_t d1 = sobol_get_dimension(context->bounce_depth, PRNG_BSDF_U);
uint32_t d2 = sobol_get_dimension(context->bounce_depth, PRNG_BSDF_V);
output.wi = random_cosine_direction(surface_data.normal, context->sample_index, d1, d2, scramble);
n_dot_l = fmaxf(glms_vec3_dot(surface_data.normal, output.wi), 0.0001f);
if (glms_vec3_dot(output.wi, context->normal) <= 0.0f)
{
output.state = PS_TERMINATE;
return output;
}
float kd_scale = (1.0f - surface_data.metallic) * (1.0f - DIELECTRIC_REFLECTIVE_F0);
vec3s kD = glms_vec3_scale(glms_vec3_one(), kd_scale);
float on = oren_nayar_eval(output.wi, V, surface_data.normal, surface_data.diffuse_roughness, n_dot_l, n_dot_v);
n_dot_l = fmaxf(glms_vec3_dot(surface_data.normal, output.wi), FLT_EPSILON);
// Diffuse bounce significantly increases spread (effectively resets or becomes very wide)
// Diffuse bounce spread
output.spread_angle = context->spread_angle + 0.5f;
vec3s diff_f = glms_vec3_scale(glms_vec3_mul(surface_data.albedo, kD), on);
// Multi-scatter GGX term (broad): sampled here with cosine.
vec3s ms_f = ggx_multi_scatter_lambert(f0, n_dot_v, n_dot_l, surface_data.roughness);
// Throughput multiplier: (f * NoL) / pdf
vec3s f_sum = glms_vec3_add(diff_f, ms_f);
f_eval = f_sum;
}
// IMPORTANT: evaluate FULL BSDF for the sampled direction (unbiased for mixture sampling)
f_eval = evaluate_bsdf_standard_lit(context, &surface_data, output.wi);
output.pdf = sample_bsdf_pdf(&surface_data, V, output.wi);
if (output.pdf < 1e-12f)
if (output.pdf < FLT_EPSILON)
{
output.state = PS_TERMINATE;
return output;