From 272141d93324f32c15b7e230b0e37d122a418f54 Mon Sep 17 00:00:00 2001
From: Keuin <keuinx@gmail.com>
Date: Fri, 15 Apr 2022 18:03:14 +0800
Subject: Add fuzzy reflective material.

---
 main_simple_scanner.cpp |  2 +-
 material_reflective.cpp | 16 +++++++++++++++-
 material_reflective.h   | 39 ++++++++++++++++++++++++++++++++++-----
 3 files changed, 50 insertions(+), 7 deletions(-)

diff --git a/main_simple_scanner.cpp b/main_simple_scanner.cpp
index 054597b..72091dd 100644
--- a/main_simple_scanner.cpp
+++ b/main_simple_scanner.cpp
@@ -50,7 +50,7 @@ void generate_image(uint16_t image_width, uint16_t image_height, double viewport
 #ifdef SCENE_REFLECT
     material_diffuse_lambertian m_ground{{0.8, 0.8, 0.0}};
     material_diffuse_lambertian m_ball_center{{0.7, 0.3, 0.3}};
-    material_reflective m_ball_left{{0.8, 0.8, 0.8}};
+    material_fuzzy_reflective m_ball_left{{0.8, 0.8, 0.8}, 1.0};
     material_reflective m_ball_right{{0.8, 0.6, 0.2}};
     // the earth
     world.add_object(std::make_shared<sphere>(vec3d{0.0, -100.5, -1.0}, 100.0, m_ground));
diff --git a/material_reflective.cpp b/material_reflective.cpp
index dc38baf..aa0d361 100644
--- a/material_reflective.cpp
+++ b/material_reflective.cpp
@@ -6,7 +6,9 @@
 #include "material.h"
 #include "material_reflective.h"
 
-bool material_reflective::scatter(ray3d &r, const object &hit_obj, double hit_t, random_uv_gen_3d &ruvg) const {
+// perfectly-smooth reflective
+template<>
+bool material_reflective_<false>::scatter(ray3d &r, const object &hit_obj, double hit_t, random_uv_gen_3d &ruvg) const {
     const auto hit_point = r.at(hit_t);
     const auto nv = hit_obj.normal_vector(hit_point);
     const auto reflected = nv.reflect(r.direction());
@@ -15,3 +17,15 @@ bool material_reflective::scatter(ray3d &r, const object &hit_obj, double hit_t,
     r.decay(albedo);
     return dot(reflected, nv) > 0;
 }
+
+// fuzzy reflective
+template<>
+bool material_reflective_<true>::scatter(ray3d &r, const object &hit_obj, double hit_t, random_uv_gen_3d &ruvg) const {
+    const auto hit_point = r.at(hit_t);
+    const auto nv = hit_obj.normal_vector(hit_point);
+    const auto reflected = nv.reflect(r.direction()) + fuzzy_.f * ruvg.range01();
+    r.source(hit_point);
+    r.direction(reflected.unit_vec());
+    r.decay(albedo);
+    return dot(reflected, nv) > 0;
+}
\ No newline at end of file
diff --git a/material_reflective.h b/material_reflective.h
index 91afa7c..64e6457 100644
--- a/material_reflective.h
+++ b/material_reflective.h
@@ -8,15 +8,44 @@
 #include "vec.h"
 #include "material.h"
 
-// metal
-class material_reflective : public material {
+template<bool cond>
+struct s_fuzzy_ {
+    // non-fuzzy material does not need these variables
+    // we remove them with an empty struct
+};
+
+template<>
+struct s_fuzzy_<true> {
+    double f; // how fuzzy the material is
+    // those are parameters that only fuzzy materials have
+};
+
+// metal with perfectly smooth surface
+template<bool Fuzzy>
+class material_reflective_ : public material {
     vec3d albedo;
+    s_fuzzy_<Fuzzy> fuzzy_;
 public:
-    explicit material_reflective(vec3d &color) : albedo(color) {}
-    explicit material_reflective(vec3d &&color) : albedo(color) {}
-    explicit material_reflective(double color) : albedo{color, color, color} {}
+    // FIXME conditionally enable these constructors by template parameter `Fuzzy`.
+
+    // Non-fuzzy constructors
+    explicit material_reflective_(vec3d &color) : albedo(color), fuzzy_{} {}
+
+    explicit material_reflective_(vec3d &&color) : albedo(color), fuzzy_{} {}
+
+    explicit material_reflective_(double color) : albedo{color, color, color}, fuzzy_{} {}
+
+    // Fuzzy constructors, with special parameters
+    explicit material_reflective_(vec3d &color, double f) : albedo(color), fuzzy_{f} {}
+
+    explicit material_reflective_(vec3d &&color, double f) : albedo(color), fuzzy_{f} {}
+
+    explicit material_reflective_(double color, double f) : albedo{color, color, color}, fuzzy_{f} {}
 
     bool scatter(ray3d &r, const object &hit_obj, double hit_t, random_uv_gen_3d &ruvg) const override;
 };
 
+using material_reflective = material_reflective_<false>;
+using material_fuzzy_reflective = material_reflective_<true>;
+
 #endif //RT_MATERIAL_REFLECTIVE_H
-- 
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