Add testrender volumes

Alongside the rest of the initialization for subpixel_radiance, an empty MediumStack is initialized. Its behavior is conceptually similar to the existing CompositeBSDF. Media are stored in a statically allocated char pool, with pointers maintained in mediums[MaxMediums]. In processing medium closures, either HomogeneousMedium or EmptyMedium are inserted into the medium stack. There is a simple priority handling scheme that will shuffle the incumbent medium pointers to give high priority mediums lower indices. They both inherit from a shared CRTP interface, Medium. When processing BSDF closures, intersections with MxDielectric or MxGeneralizedSchlick may only be added when priority < current_priority or are both 0 (the precious priority). MediumStack exposes an integrate method that operates on aggregated parameters from all media sharing the same priority as the topmost medium; these aggregated parameters are stored on the stack and updated whenever media are added. A CDF built from these parameters is then sampled to select one of the overlapping media for scattering. At present, only Henyey–Greenstein phase functions are supported, implemented as a BSDF subclass.

Signed-off-by: Owen O'Malley <theowen@email.com>

Author: ThyOwen

src/cmake/testing.cmake

@@ -362,6 +362,7 @@ macro (osl_add_all_tests)
                 render-cornell
                 render-displacement
                 render-furnace-diffuse
+                render-mx-anisotropic-vdf
                 render-mx-furnace-burley-diffuse
                 render-mx-furnace-oren-nayar
                 render-mx-furnace-sheen
@@ -371,7 +372,9 @@ macro (osl_add_all_tests)
                 render-mx-generalized-schlick render-mx-generalized-schlick-glass
                 render-mx-layer
                 render-mx-sheen
-                render-microfacet render-oren-nayar
+                render-mx-medium-vdf
+                render-mx-medium-vdf-glass
+		render-microfacet render-oren-nayar
                 render-spi-thinlayer
                 render-uv render-veachmis render-ward
                 render-raytypes

src/testrender/shading.cpp

@@ -1513,6 +1513,92 @@ struct ZeltnerBurleySheen final : public BSDF, MxSheenParams {
     }
 };
 
+
+struct HenyeyGreenstein final : public BSDF {
+    const float g;
+    OSL_HOSTDEVICE HenyeyGreenstein(float g) : BSDF(this), g(g) {}
+
+    static OSL_HOSTDEVICE float PhaseHG(float cos_theta, float g)
+    {
+        const float denom = 1 + g * g + 2 * g * cos_theta;
+        return (1 - g * g) / (4 * M_PI * denom * sqrtf(denom));
+    }
+
+    OSL_HOSTDEVICE Sample eval(const Vec3& wo, const Vec3& wi) const
+    {
+        const float pdf = PhaseHG(dot(wo, wi), g);
+        return { wi, Color3(pdf), pdf, 0.0f };
+    }
+
+    OSL_HOSTDEVICE Sample sample(const Vec3& wo, float rx, float ry,
+                                 float rz) const
+    {
+        TangentFrame frame = TangentFrame::from_normal(wo);
+
+        float cos_theta;
+        if (abs(g) < 1e-3f) {
+            cos_theta = 1.0f - 2.0f * rx;
+        } else {
+            float sqr_term = (1 - g * g) / (1 - g + 2 * g * rx);
+            cos_theta      = (1 + g * g - sqr_term * sqr_term) / (2 * g);
+            cos_theta      = OIIO::clamp(cos_theta, -1.0f, 1.0f);
+        }
+
+        float sin_theta = sqrtf(
+            OIIO::clamp(1.0f - cos_theta * cos_theta, 0.0f, 1.0f));
+        float phi     = 2 * M_PI * ry;
+        Vec3 local_wi = Vec3(sin_theta * cosf(phi), sin_theta * sinf(phi),
+                             cos_theta);
+
+        Vec3 wi       = frame.toworld(local_wi);
+        float pdf_val = PhaseHG(cos_theta, g);
+
+        return { wi, Color3(1.0f), pdf_val, 0.0f };
+    }
+};
+
+struct HomogeneousMedium final : public Medium {
+    MediumParams params;
+    HenyeyGreenstein phase_func;
+
+    OSL_HOSTDEVICE HomogeneousMedium(const MediumParams& params)
+        : Medium(this), params(params), phase_func(params.medium_g)
+    {
+    }
+
+    OSL_HOSTDEVICE BSDF::Sample sample_phase_func(const Vec3& wo, float rx,
+                                                  float ry, float rz) const
+    {
+        return phase_func.sample(wo, rx, ry, rz);
+    }
+
+    OSL_HOSTDEVICE const MediumParams* get_params() const { return &params; }
+};
+
+struct EmptyMedium final : public Medium {
+    MediumParams params;
+
+    OSL_HOSTDEVICE EmptyMedium(const MediumParams& params)
+        : Medium(this), params(params)
+    {
+    }
+
+    OSL_HOSTDEVICE const MediumParams* get_params() const { return &params; }
+
+    OSL_HOSTDEVICE Medium::Sample sample(Ray& ray, Sampler& sampler,
+                                         Intersection& hit) const
+    {
+        return { 0.0f, Color3(1.0f), Color3(1.0f) };
+    }
+
+    OSL_HOSTDEVICE BSDF::Sample sample_phase_func(const Vec3& wo, float rx,
+                                                  float ry, float rz) const
+    {
+        return { Vec3(1.0f), Color3(1.0f), 0.0f, 0.0f };
+    }
+};
+
+
 OSL_HOSTDEVICE Color3
 evaluate_layer_opacity(const ShaderGlobalsType& sg, float path_roughness,
                        const ClosureColor* closure)
@@ -1606,8 +1692,8 @@ evaluate_layer_opacity(const ShaderGlobalsType& sg, float path_roughness,
 
 OSL_HOSTDEVICE void
 process_medium_closure(const ShaderGlobalsType& sg, float path_roughness,
-                       ShadingResult& result, const ClosureColor* closure,
-                       const Color3& w)
+                       ShadingResult& result, MediumStack& medium_stack,
+                       const ClosureColor* closure, const Color3& w)
 {
     if (!closure)
         return;
@@ -1649,37 +1735,72 @@ process_medium_closure(const ShaderGlobalsType& sg, float path_roughness,
             const ClosureComponent* comp = closure->as_comp();
             Color3 cw                    = weight * comp->w;
             const auto& params           = *comp->as<MxAnisotropicVdfParams>();
-            result.sigma_t               = cw * params.extinction;
-            result.sigma_s               = params.albedo * result.sigma_t;
-            result.medium_g              = params.anisotropy;
-            closure                      = nullptr;
+            result.medium_data.sigma_t   = cw * params.extinction;
+            result.medium_data.sigma_s   = params.albedo
+                                         * result.medium_data.sigma_t;
+            result.medium_data.medium_g = params.anisotropy;
+            result.medium_data.priority = 0;
+
+            if (!sg.backfacing) {  // if entering
+                if (result.medium_data.is_vaccum()) {
+                    medium_stack.add_medium<EmptyMedium>(result.medium_data);
+                } else {
+                    medium_stack.add_medium<HomogeneousMedium>(
+                        result.medium_data);
+                }
+            }
+
+            closure = nullptr;
             break;
         }
         case MX_MEDIUM_VDF_ID: {
             const ClosureComponent* comp = closure->as_comp();
             Color3 cw                    = weight * comp->w;
             const auto& params           = *comp->as<MxMediumVdfParams>();
-            result.sigma_t = { -OIIO::fast_log(params.transmission_color.x),
-                               -OIIO::fast_log(params.transmission_color.y),
-                               -OIIO::fast_log(params.transmission_color.z) };
-            // NOTE: closure weight scales the extinction parameter
-            result.sigma_t *= cw / params.transmission_depth;
-            result.sigma_s  = params.albedo * result.sigma_t;
-            result.medium_g = params.anisotropy;
-            // TODO: properly track a medium stack here ...
-            result.refraction_ior = sg.backfacing ? 1.0f / params.ior
-                                                  : params.ior;
-            result.priority       = params.priority;
-            closure               = nullptr;
+
+            result.medium_data.sigma_t
+                = Color3(-OIIO::fast_log(params.transmission_color.x),
+                         -OIIO::fast_log(params.transmission_color.y),
+                         -OIIO::fast_log(params.transmission_color.z));
+
+            result.medium_data.sigma_t *= cw / params.transmission_depth;
+            result.medium_data.sigma_s = params.albedo
+                                         * result.medium_data.sigma_t;
+            result.medium_data.medium_g = params.anisotropy;
+
+            result.medium_data.refraction_ior = sg.backfacing
+                                                    ? 1.0f / params.ior
+                                                    : params.ior;
+            result.medium_data.priority       = params.priority;
+
+            if (!sg.backfacing) {  // if entering
+                if (result.medium_data.is_vaccum()) {
+                    medium_stack.add_medium<EmptyMedium>(result.medium_data);
+                } else {
+                    medium_stack.add_medium<HomogeneousMedium>(
+                        result.medium_data);
+                }
+            }
+
+            closure = nullptr;
             break;
         }
         case MxDielectric::closureid(): {
             const ClosureComponent* comp     = closure->as_comp();
             const MxDielectric::Data& params = *comp->as<MxDielectric::Data>();
             if (!is_black(weight * comp->w * params.refr_tint)) {
-                // TODO: properly track a medium stack here ...
-                result.refraction_ior = sg.backfacing ? 1.0f / params.IOR
-                                                      : params.IOR;
+                float new_ior = sg.backfacing ? 1.0f / params.IOR : params.IOR;
+
+                result.medium_data.refraction_ior = new_ior;
+
+                const MediumParams* current_params
+                    = medium_stack.get_current_params();
+                if (current_params
+                    && result.medium_data.priority
+                           <= current_params->priority) {
+                    result.medium_data.refraction_ior
+                        = current_params->refraction_ior;
+                }
             }
             closure = nullptr;
             break;
@@ -1688,13 +1809,23 @@ process_medium_closure(const ShaderGlobalsType& sg, float path_roughness,
             const ClosureComponent* comp = closure->as_comp();
             const auto& params = *comp->as<MxGeneralizedSchlickParams>();
             if (!is_black(weight * comp->w * params.transmission_tint)) {
-                // TODO: properly track a medium stack here ...
                 float avg_F0  = clamp((params.f0.x + params.f0.y + params.f0.z)
                                           / 3.0f,
                                       0.0f, 0.99f);
                 float sqrt_F0 = sqrtf(avg_F0);
                 float ior     = (1 + sqrt_F0) / (1 - sqrt_F0);
-                result.refraction_ior = sg.backfacing ? 1.0f / ior : ior;
+                float new_ior = sg.backfacing ? 1.0f / ior : ior;
+
+                result.medium_data.refraction_ior = new_ior;
+
+                const MediumParams* current_params
+                    = medium_stack.get_current_params();
+                if (current_params
+                    && result.medium_data.priority
+                           <= current_params->priority) {
+                    result.medium_data.refraction_ior
+                        = current_params->refraction_ior;
+                }
             }
             closure = nullptr;
             break;
@@ -1711,8 +1842,9 @@ process_medium_closure(const ShaderGlobalsType& sg, float path_roughness,
 // recursively walk through the closure tree, creating bsdfs as we go
 OSL_HOSTDEVICE void
 process_bsdf_closure(const ShaderGlobalsType& sg, float path_roughness,
-                     ShadingResult& result, const ClosureColor* closure,
-                     const Color3& w, bool light_only)
+                     ShadingResult& result, MediumStack& medium_stack,
+                     const ClosureColor* closure, const Color3& w,
+                     bool light_only)
 {
     static const ustringhash uh_ggx("ggx");
     static const ustringhash uh_beckmann("beckmann");
@@ -1845,9 +1977,16 @@ process_bsdf_closure(const ShaderGlobalsType& sg, float path_roughness,
                 case MxDielectric::closureid(): {
                     const MxDielectric::Data& params
                         = *comp->as<MxDielectric::Data>();
-                    ok = result.bsdf.add_bsdf<MxDielectric>(cw, params, -sg.I,
-                                                            sg.backfacing,
-                                                            path_roughness);
+
+                    if (medium_stack.false_intersection_with(
+                            result.medium_data)) {
+                        ok = result.bsdf.add_bsdf<Transparent>(cw);
+                    } else {
+                        ok = result.bsdf.add_bsdf<MxDielectric>(cw, params,
+                                                                -sg.I,
+                                                                sg.backfacing,
+                                                                path_roughness);
+                    }
                     break;
                 }
                 case MxConductor::closureid(): {
@@ -1860,15 +1999,21 @@ process_bsdf_closure(const ShaderGlobalsType& sg, float path_roughness,
                 case MX_GENERALIZED_SCHLICK_ID: {
                     const MxGeneralizedSchlickParams& params
                         = *comp->as<MxGeneralizedSchlickParams>();
-                    if (is_black(params.transmission_tint))
-                        ok = result.bsdf.add_bsdf<MxMicrofacet<
-                            MxGeneralizedSchlickParams, GGXDist, false>>(cw,
-                                                                         params,
-                                                                         1.0f);
-                    else
-                        ok = result.bsdf.add_bsdf<MxMicrofacet<
-                            MxGeneralizedSchlickParams, GGXDist, true>>(
-                            cw, params, result.refraction_ior);
+
+                    if (medium_stack.false_intersection_with(
+                            result.medium_data)) {
+                        ok = result.bsdf.add_bsdf<Transparent>(cw);
+                    } else {
+                        if (is_black(params.transmission_tint)) {
+                            ok = result.bsdf.add_bsdf<MxMicrofacet<
+                                MxGeneralizedSchlickParams, GGXDist, false>>(
+                                cw, params, 1.0f);
+                        } else {
+                            ok = result.bsdf.add_bsdf<MxMicrofacet<
+                                MxGeneralizedSchlickParams, GGXDist, true>>(
+                                cw, params, result.medium_data.refraction_ior);
+                        }
+                    }
                     break;
                 };
                 case MX_TRANSLUCENT_ID: {
@@ -1957,11 +2102,14 @@ process_bsdf_closure(const ShaderGlobalsType& sg, float path_roughness,
 
 OSL_HOSTDEVICE void
 process_closure(const ShaderGlobalsType& sg, float path_roughness,
-                ShadingResult& result, const ClosureColor* Ci, bool light_only)
+                ShadingResult& result, MediumStack& medium_stack,
+                const ClosureColor* Ci, bool light_only)
 {
     if (!light_only)
-        process_medium_closure(sg, path_roughness, result, Ci, Color3(1));
-    process_bsdf_closure(sg, path_roughness, result, Ci, Color3(1), light_only);
+        process_medium_closure(sg, path_roughness, result, medium_stack, Ci,
+                               Color3(1));
+    process_bsdf_closure(sg, path_roughness, result, medium_stack, Ci,
+                         Color3(1), light_only);
 }
 
 OSL_HOSTDEVICE Vec3
@@ -2022,5 +2170,19 @@ BSDF::sample_vrtl(const Vec3& wo, float rx, float ry, float rz) const
     return dispatch([&](auto bsdf) { return bsdf.sample(wo, rx, ry, rz); });
 }
 
+OSL_HOSTDEVICE BSDF::Sample
+Medium::sample_phase_func_vrtl(const Vec3& wo, float rx, float ry,
+                               float rz) const
+{
+    return dispatch([&](const auto& medium) {
+        return medium.sample_phase_func(wo, rx, ry, rz);
+    });
+}
+
+OSL_HOSTDEVICE const MediumParams*
+Medium::get_params_vrtl() const
+{
+    return dispatch([&](const auto& medium) { return medium.get_params(); });
+}
 
 OSL_NAMESPACE_END