#include "Material/SimpleLit.h" #include "Algorithm/BSDF.h" #include "Algorithm/Sobol.h" #include static float DIELECTRIC_REFLECTIVE_F0 = 0.04f; // Standard dielectric reflectivity coef at incident angle (= 4%) static vec3s DIELECTRIC_REFLECTIVE = {0.04f, 0.04f, 0.04f}; // Standard dielectric reflectivity coef at incident angle (= 4%) void simple_lit_data_default(const shading_context_t* context, const void* properties, void* data_out) { const simple_lit_properties_t* prop = (simple_lit_properties_t*)properties; simple_lit_data_t* data = (simple_lit_data_t*)data_out; data->albedo = prop->albedo; const texture_t* albedo_texture = get_texture(context->textures, prop->albedo_texture); if (albedo_texture != NULL && albedo_texture->data != NULL) { data->albedo = glms_vec3_mul(data->albedo, glms_vec3(texture_sample(albedo_texture, context->uv.x, context->uv.y))); } data->roughness = prop->roughness; const texture_t* roughness_texture = get_texture(context->textures, prop->roughness_texture); if (roughness_texture != NULL && roughness_texture->data != NULL) { data->roughness = data->roughness * texture_sample(roughness_texture, context->uv.x, context->uv.y).x; } data->metallic = prop->metallic; const texture_t* metallic_texture = get_texture(context->textures, prop->metallic_texture); if (metallic_texture != NULL && metallic_texture->data != NULL) { data->metallic = data->metallic * texture_sample(metallic_texture, context->uv.x, context->uv.y).x; } } // Simple lit, but keep it unbiased as much as possible vec3s sample_bsdf_simple_lit(const shading_context_t* context, const void* properties, const compute_surface_data_f compute_surface_data, uint32_t sample_index, uint32_t bounce, float* pdf_out) { simple_lit_data_t shading_data; compute_surface_data(context, properties, &shading_data); //TODO: having a bsdf data struct to avoid recomputing the same thing in both sample and evaluate vec3s f0 = glms_vec3_lerp(DIELECTRIC_REFLECTIVE, shading_data.albedo, shading_data.metallic); float cos_theta_0 = fmaxf(glms_vec3_dot(context->normal, context->wo), 0.0f); vec3s f = fresnel_schlick_vec3(f0, cos_theta_0); float lum_f = (f.x + f.y + f.z) / 3.0f; float prob_specular = glm_lerp(lum_f, 1.0f, shading_data.metallic); float prob_diffuse = (1.0f - shading_data.metallic) * (1.0f - lum_f); // Diffuse only for non-metals, reduced by reflection float total_prob = prob_diffuse + prob_specular; if (total_prob < FLT_EPSILON) { *pdf_out = 0.0f; return glms_vec3_zero(); } // Normalize probabilities // total_prob should be 1.0f, worth it? Maybe still need to avoid floating point errors prob_diffuse /= total_prob; prob_specular /= total_prob; vec3s wi; float lob_sample = sobol_sample(sample_index, sobol_get_dimension(bounce, PRNG_BSDF)); uint16_t d1 = sobol_get_dimension(bounce, PRNG_BSDF_U); uint16_t d2 = sobol_get_dimension(bounce, PRNG_BSDF_V); if (lob_sample < prob_diffuse) // Diffuse Lobe { wi = random_cosine_direction(context->normal, sample_index, d1, d2); } else // Specular Lobe { // For simplification we use blinn-phong lobe distribution, we will implement GGX for standard lit later // When talking about simplification, wen even can use a simple interpolation bwtween roughness and wi, but it's too biased. // A common simplification involves sampling spherical coordinates(theta and phi angles) related to normal such that cose(theta) is distributed according to the Blinn-Phong distribution // We can use a inversion sampling where cos(theta) = powf(random_float(), 1.0f / (specular_exponent + 1.0f)) and phi = 2 * PI * random_float() float specular_exponent = roughness_to_blinn_phong_specular_exponent(shading_data.roughness); float theta = acosf(powf(sobol_sample(sample_index, d1), 1.0f / (specular_exponent + 1.0f))); float phi = 2.0f * (float)M_PI * sobol_sample(sample_index, d2); // float theta = acosf(powf(random_float(), 1.0f / (specular_exponent + 1.0f))); // float phi = 2.0f * (float)M_PI * random_float(); vec3s h_ts = (vec3s) { sinf(theta) * cosf(phi), sinf(theta) * sinf(phi), cosf(theta) }; vec3s tangent_u; // World-space tangent (U) vec3s bitangent_v; // World-space bitangent (V) create_orthonormal_basis(context->normal, &tangent_u, &bitangent_v); vec3s scaled_u = glms_vec3_scale(tangent_u, h_ts.x); vec3s scaled_v = glms_vec3_scale(bitangent_v, h_ts.y); vec3s scaled_n = glms_vec3_scale(context->normal, h_ts.z); // Transform h from tangent space to world space vec3s h_ws; h_ws = glms_vec3_add(scaled_u, scaled_v); h_ws = glms_vec3_add(h_ws, scaled_n); h_ws = glms_vec3_normalize(h_ws); // wi is simple now, just reflect wo around normal wi = glms_vec3_reflect(glms_vec3_negate(context->wo), h_ws); } // Final check to ensure wi is in the correct hemisphere if (glms_vec3_dot(wi, context->normal) < 0.0f) { *pdf_out = 0.0f; return glms_vec3_zero(); } float pdf_diffuse = pdf_cosine_weighted_hemisphere(context->normal, wi); float pdf_specular = pdf_blinn_phong_lobe(context->normal, wi, context->wo, shading_data.roughness); *pdf_out = prob_diffuse * pdf_diffuse + prob_specular * pdf_specular; return wi; } float sample_bsdf_pdf_simple_lit(const shading_context_t* context, const void* properties, const compute_surface_data_f compute_surface_data) { // If wi is below the horizon relative to the normal, PDF must be 0 if (glms_vec3_dot(context->normal, context->wi) <= 0.0f) // Use <= to be safe { return 0.0f; } simple_lit_data_t shading_data; compute_surface_data(context, properties, &shading_data); // Again, we need bsdf data; vec3s f0 = glms_vec3_lerp(DIELECTRIC_REFLECTIVE, shading_data.albedo, shading_data.metallic); float cos_theta_o = fmaxf(glms_vec3_dot(context->normal, context->wo), 0.0f); // Use 'o' for outgoing (wo) float F = glms_vec3_max(fresnel_schlick_vec3(f0, cos_theta_o)); float prob_specular = glm_lerp(F, 1.0f, shading_data.metallic); float prob_diffuse = (1.0f - shading_data.metallic) * (1.0f - F); float total_prob = prob_diffuse + prob_specular; if (total_prob < FLT_EPSILON) { return 0.0f; // No probability of scattering } prob_diffuse /= total_prob; prob_specular /= total_prob; float pdf_diff = pdf_cosine_weighted_hemisphere(context->normal, context->wi); float diffuse_pdf_component = prob_diffuse * pdf_diff; float pdf_spec = pdf_blinn_phong_lobe(context->normal, context->wo, context->wi, shading_data.roughness); float specular_pdf_component = prob_specular * pdf_spec; return diffuse_pdf_component + specular_pdf_component; } vec3s evaluate_bsdf_simple_lit(const shading_context_t* context, const void* properties, const compute_surface_data_f compute_surface_data) { simple_lit_data_t shading_data; compute_surface_data(context, properties, &shading_data); vec3s h = glms_vec3_normalize(glms_vec3_add(context->wi, context->wo)); float n_dot_l = fmaxf(FLT_EPSILON, glms_vec3_dot(context->normal, context->wi)); float n_dot_v = fmaxf(FLT_EPSILON, glms_vec3_dot(context->normal, context->wo)); float n_dot_h = glms_vec3_dot(context->normal, h); float v_dot_h = glms_vec3_dot(context->wo, h); vec3s f0 = glms_vec3_lerp(DIELECTRIC_REFLECTIVE, shading_data.albedo, shading_data.metallic); vec3s diffuse_color = glms_vec3_scale(shading_data.albedo, 1.0f - shading_data.metallic); vec3s diffuse_term = glms_vec3_scale(diffuse_color, (float)M_1_PI); float specular_exponent = roughness_to_blinn_phong_specular_exponent(shading_data.roughness); // Normalization factor D (Blinn-Phong distribution) float D_norm = (specular_exponent + 2.0f) / (2.0f * (float)M_PI); // Common normalization float D = D_norm * powf(n_dot_h, specular_exponent); vec3s F = fresnel_schlick_vec3(f0, v_dot_h); float denominator = 4.0f * n_dot_l * n_dot_v; if (denominator < FLT_EPSILON) { return diffuse_term; } vec3s specular_term = glms_vec3_scale(F, D / denominator); // Specular term (Blinn-Phong), we assume that G = 1.0f for simplicity return glms_vec3_add(diffuse_term, specular_term); }