Anisotropic metals, stage 1

Author: pmudry

resources/scenes/01_anisotropic_metals_test.yaml

@@ -0,0 +1,145 @@
+# Anisotropic Metals Test Scene
+# Demonstrates the GGX microfacet anisotropic conductor materials
+#
+# Back row  (gold): SAME roughness (0.45), VARYING anisotropy: 0.0 → 0.5 → 0.95
+# Front row (gold): SAME anisotropy (0.8), VARYING roughness:  0.15 → 0.35 → 0.6
+# This isolates each variable so the effect is clearly visible.
+
+camera:
+  position: [0, 3.5, 7]
+  look_at: [0, 0.3, -1]
+  fov: 38
+
+settings:
+  use_bvh: true
+  background_color: [0.04, 0.04, 0.8]
+  background_intensity: 0.05
+  adaptive_sampling: false
+
+materials:
+  - name: "ground"
+    type: "lambertian"
+    albedo: [0.4, 0.4, 0.4]
+
+  - name: "light_top"
+    type: "light"
+    color: [1.0, 0.875, 0.75]
+    emission_intensity: 8    
+
+  - name: "light_side"
+    type: "light"
+    color: [1.0, 0.875, 0.75]
+    emission_intensity: 2
+
+  # --- Back row: SAME roughness 0.45, VARYING anisotropy ---
+  - name: "gold_aniso_00"
+    type: "anisotropic_metal"
+    roughness: 0.45
+    anisotropy: 0.0
+    preset: "gold"
+
+  - name: "gold_aniso_50"
+    type: "anisotropic_metal"
+    roughness: 0.45
+    anisotropy: 0.5
+    preset: "gold"
+
+  - name: "gold_aniso_95"
+    type: "anisotropic_metal"
+    roughness: 0.45
+    anisotropy: 0.95
+    preset: "gold"
+
+  # --- Front row: SAME anisotropy 0.8, VARYING roughness ---
+  - name: "gold_rough_15"
+    type: "anisotropic_metal"
+    roughness: 0.15
+    anisotropy: 0.8
+    preset: "gold"
+
+  - name: "gold_rough_35"
+    type: "anisotropic_metal"
+    roughness: 0.35
+    anisotropy: 0.8
+    preset: "gold"
+
+  - name: "gold_rough_60"
+    type: "anisotropic_metal"
+    roughness: 0.6
+    anisotropy: 0.8
+    preset: "gold"
+
+  # Colored walls for visible environment reflections
+  - name: "wall_red"
+    type: "lambertian"
+    albedo: [0.85, 0.12, 0.12]
+
+  - name: "wall_blue"
+    type: "lambertian"
+    albedo: [0.12, 0.12, 0.85]
+
+geometry:
+  # Ground
+  - type: "sphere"
+    material: "ground"
+    center: [0, -1000, -1]
+    radius: 1000
+
+  # Top area light (narrow strip to show anisotropic stretching)
+  - type: "rectangle"
+    material: "light_top"
+    corner: [-1.0, 5, -3]
+    u: [2.0, 0, 0]
+    v: [0, 0, 4]
+
+  # Side fill light
+  - type: "rectangle"
+    material: "light_side"
+    corner: [5, 1, -4]
+    u: [0, 2, 0]
+    v: [0, 0, 4]
+
+  # --- Back row: varying anisotropy (left=isotropic, right=brushed) ---
+  - type: "sphere"
+    material: "gold_aniso_00"
+    center: [-2.5, 0.8, -2.5]
+    radius: 0.8
+
+  - type: "sphere"
+    material: "gold_aniso_50"
+    center: [0, 0.8, -2.5]
+    radius: 0.8
+
+  - type: "sphere"
+    material: "gold_aniso_95"
+    center: [2.5, 0.8, -2.5]
+    radius: 0.8
+
+  # --- Front row: varying roughness (left=smooth, right=rough) ---
+  - type: "sphere"
+    material: "gold_rough_15"
+    center: [-2.5, 0.8, 0.5]
+    radius: 0.8
+
+  - type: "sphere"
+    material: "gold_rough_35"
+    center: [0, 0.8, 0.5]
+    radius: 0.8
+
+  - type: "sphere"
+    material: "gold_rough_60"
+    center: [2.5, 0.8, 0.5]
+    radius: 0.8
+
+  # Colored side walls (provide reflectable environment)
+  - type: "rectangle"
+    material: "wall_red"
+    corner: [-6, 0, -5]
+    u: [0, 4, 0]
+    v: [0, 0, 8]
+
+  - type: "rectangle"
+    material: "wall_blue"
+    corner: [6, 0, -5]
+    u: [0, 4, 0]
+    v: [0, 0, 8]

resources/scenes/03_platonic_solids.yaml

@@ -7,8 +7,8 @@ camera:
   fov: 40
 
 settings:
-  background_color: [0.08, 0.08, 0.12]
-  background_intensity: 0.2
+  background_color: [0.04, 0.04, 0.8]
+  background_intensity: 0.1
   use_bvh: true
 
 materials:
@@ -38,11 +38,13 @@ materials:
 
   - name: "area_light"
     type: "light"
-    emission: [12, 11, 10]
+    color: [1.0, 0.875, 0.75]
+    emission_intensity: 8
 
   - name: "fill_light"
     type: "light"
-    emission: [3, 3, 4]
+    color: [1.0, 1.167, 1.0]
+    emission_intensity: 6
 
 geometry:
   - type: "rectangle"
@@ -61,7 +63,7 @@ geometry:
   # Fill light (behind camera, subtle)
   - type: "rectangle"
     material: "fill_light"
-    corner: [-2, 3, 8]
+    corner: [-2, 3, -8]
     u: [4, 0, 0]
     v: [0, 0, 1]
     visible: false
@@ -72,33 +74,33 @@ geometry:
   - type: "obj"
     material: "isc_yellow"
     file: "../models/tetrahedron.obj"
-    position: [-4, 0.5, 0]
-    scale: [1.0, 1.0, 1.0]
+    position: [-4, 0.8, 0]
+    scale: [0.8, 0.8, 0.8]
 
   # 2. Cube (6 faces) - ISC Blue
   - type: "obj"
     material: "isc_blue"
     file: "../models/cube.obj"
-    position: [-2, 0.1, 0]
-    scale: [1.0, 1.0, 1.0]
+    position: [-2, 0.8, 0]
+    scale: [0.8, 0.8, 0.8]
 
   # 3. Octahedron (8 faces) - ISC Violet
   - type: "obj"
     material: "isc_violet"
     file: "../models/octahedron.obj"
-    position: [0, 0.5, 0]
-    scale: [1.0, 1.0, 1.0]
+    position: [0, 0.8, 0]
+    scale: [0.8, 0.8, 0.8]
 
   # 4. Dodecahedron (12 faces) - ISC Rose
   - type: "obj"
     material: "isc_rose"
     file: "../models/dodecahedron.obj"
-    position: [2, 0.1, 0]
-    scale: [1.0, 1.0, 1.0]
+    position: [2, 0.8, 0]
+    scale: [0.8, 0.8, 0.8]
 
   # 5. Icosahedron (20 faces) - ISC Green
   - type: "obj"
     material: "isc_green"
     file: "../models/icosahedron.obj"
-    position: [4, 0.5, 0]
-    scale: [1.0, 1.0, 1.0]
+    position: [4, 0.8, 0]
+    scale: [0.8, 0.8, 0.8]

src/rayon/constants.hpp

@@ -6,7 +6,7 @@ namespace constants
 {
     const std::string ver_major = "1";
     const std::string ver_minor = "5";
-    const std::string ver_patch = "2";
+    const std::string ver_patch = "5";
     const std::string version = ver_major + "." + ver_minor + "." + ver_patch;
 
     // Image specifics settings

src/rayon/gpu_renderers/cuda_raytracer.cuh

@@ -3,6 +3,7 @@
 #include "cuda_float3.cuh"
 #include "cuda_scene.cuh"
 #include "cuda_utils.cuh"
+#include "microfacet_ggx.cuh"
 
 #include <cfloat>
 #include <cmath>
@@ -47,20 +48,25 @@ enum LegacyMaterialType
    LIGHT = 3,
    ROUGH_MIRROR = 4,
    CONSTANT = 5,
-   SHOW_NORMALS = 6
+   SHOW_NORMALS = 6,
+   ANISOTROPIC_METAL = 7
 };
 
 struct hit_record_simple
 {
    f3 p, normal;
+   f3 tangent;          // Surface tangent for anisotropic materials
    float t;
    bool front_face;
    LegacyMaterialType material;
    f3 color;
    float refractive_index;
    f3 emission;
    float roughness;
-   bool visible; // Whether the hit geometry is visible (invisible geometry still emits light)
+   float anisotropy;    // Anisotropy ratio [0-1]
+   f3 eta;              // Complex IOR real part (conductor Fresnel)
+   f3 k_extinction;     // Complex IOR imaginary part (conductor Fresnel)
+   bool visible;        // Whether the hit geometry is visible (invisible geometry still emits light)
 };
 
 //==============================================================================
@@ -209,6 +215,12 @@ __device__ inline bool hit_sphere(const f3 &center, float radius, const ray_simp
    f3 outward_normal = (rec.p - center) / radius;
    rec.front_face = dot(r.dir, outward_normal) < 0;
    rec.normal = rec.front_face ? outward_normal : f3(-outward_normal.x, -outward_normal.y, -outward_normal.z);
+   // Compute tangent for anisotropic materials (azimuthal direction)
+   f3 up_dir(0.0f, 1.0f, 0.0f);
+   f3 tangent = cross(up_dir, outward_normal);
+   if (tangent.length_squared() < 1e-6f)
+      tangent = f3(1.0f, 0.0f, 0.0f); // Degenerate at poles
+   rec.tangent = normalize(tangent);
    return true;
 }
 
@@ -245,6 +257,8 @@ __device__ inline bool hit_rectangle(const f3 &corner, const f3 &u, const f3 &v,
    rec.p = intersection;
    rec.front_face = dot(r.dir, normal) < 0;
    rec.normal = rec.front_face ? normal : f3(-normal.x, -normal.y, -normal.z);
+   // Compute tangent for anisotropic materials (along u edge)
+   rec.tangent = normalize(u);
    return true;
 }
 
@@ -306,6 +320,8 @@ __device__ inline bool hit_triangle(const f3 &v0, const f3 &v1, const f3 &v2,
    }
 
    rec.normal = rec.front_face ? shading_normal : f3(-shading_normal.x, -shading_normal.y, -shading_normal.z);
+   // Compute tangent for anisotropic materials (along edge v0->v1)
+   rec.tangent = normalize(edge1);
    return true;
 }
 
@@ -414,6 +430,14 @@ __device__ __forceinline__ void apply_material(const CudaScene::Material &mat, h
    case MaterialType::SHOW_NORMALS:
       rec.material = SHOW_NORMALS;
       break;
+   case MaterialType::ANISOTROPIC_METAL:
+      rec.material = ANISOTROPIC_METAL;
+      rec.color = mat.albedo;
+      rec.roughness = mat.roughness;
+      rec.anisotropy = mat.anisotropy;
+      rec.eta = mat.eta;
+      rec.k_extinction = mat.k;
+      break;
    case MaterialType::SDF_MATERIAL: // TODO: Implement SDF materials
       rec.material = LAMBERTIAN;
       rec.color = mat.albedo;
@@ -632,6 +656,66 @@ __device__ __forceinline__ bool scatter_material(const hit_record_simple &rec, c
       emitted = 0.5f * (rec.normal + f3(1.0f, 1.0f, 1.0f));
       return false;
    }
+   case ANISOTROPIC_METAL:
+   {
+      // Anisotropic GGX microfacet conductor (PBR Book §9.6)
+
+      // Convert roughness + anisotropy to alpha_x/alpha_y (Disney convention)
+      float aspect = sqrtf(fmaxf(1e-4f, 1.0f - 0.9f * rec.anisotropy));
+      float r2 = rec.roughness * rec.roughness;
+      float alpha_x = fmaxf(1e-4f, r2 / aspect);
+      float alpha_y = fmaxf(1e-4f, r2 * aspect);
+
+      // Effectively smooth: fall back to perfect mirror with Fresnel tint
+      if (fmaxf(alpha_x, alpha_y) < 1e-3f)
+      {
+         f3 refl = reflect(normalize(current_ray.dir), rec.normal);
+         scattered_ray = ray_simple(rec.p + 0.0001f * rec.normal, refl);
+         float cos_i = fmaxf(dot(-normalize(current_ray.dir), rec.normal), 0.0f);
+         attenuation = FrComplex(cos_i, rec.eta, rec.k_extinction);
+         return dot(refl, rec.normal) > 0.0f;
+      }
+
+      // Build TBN frame (tangent, bitangent, normal)
+      f3 N = normalize(rec.normal);
+      f3 T = normalize(rec.tangent - dot(rec.tangent, N) * N); // Re-orthogonalize
+      f3 B = cross(N, T);
+
+      // Transform outgoing direction (toward viewer) to local shading space
+      f3 wo_world = normalize(f3(-current_ray.dir.x, -current_ray.dir.y, -current_ray.dir.z));
+      f3 wo_local(dot(wo_world, T), dot(wo_world, B), dot(wo_world, N));
+
+      // Ensure wo is in upper hemisphere
+      if (wo_local.z <= 0.0f)
+         return false;
+
+      // Sample microfacet normal via VNDF
+      f3 wm = Sample_wm_GGX(wo_local, alpha_x, alpha_y,
+                              rand_float(state), rand_float(state));
+
+      // Reflect wo around wm to get wi
+      f3 wi_local = reflect(f3(-wo_local.x, -wo_local.y, -wo_local.z), wm);
+
+      // Check that reflected direction is in upper hemisphere
+      if (wi_local.z <= 0.0f)
+         return false;
+
+      // Transform wi back to world space
+      f3 wi_world = wi_local.x * T + wi_local.y * B + wi_local.z * N;
+
+      // Compute Fresnel reflectance at microfacet
+      float cos_theta_i = fmaxf(dot(wo_local, wm), 0.0f);
+      f3 F = FrComplex(cos_theta_i, rec.eta, rec.k_extinction);
+
+      // VNDF importance sampling weight: F * G(wo,wi) / G1(wo)
+      float G = G_GGX(wo_local, wi_local, alpha_x, alpha_y);
+      float G1 = G1_GGX(wo_local, alpha_x, alpha_y);
+      f3 weight = F * (G / fmaxf(G1, 1e-6f));
+
+      scattered_ray = ray_simple(rec.p + 0.0001f * rec.normal, wi_world);
+      attenuation = weight;
+      return true;
+   }
    default:
       return false;
    }