From e46e1c4033b9d96325de3295eb442a5b1fa19f19 Mon Sep 17 00:00:00 2001
From: Keuin <keuinx@gmail.com>
Date: Wed, 13 Apr 2022 23:31:47 +0800
Subject: Global diffuse lighting. (gamma not corrected) Some operations on
 pixel<T>. Make ray3 support copy semantic. Fix vec3 operands does not filter
 out vec3-vec3 as parameters. random_uv_gen generating random unit vectors.

---
 hitlist.h | 85 ++++++++++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 54 insertions(+), 31 deletions(-)

(limited to 'hitlist.h')

diff --git a/hitlist.h b/hitlist.h
index 0c65e1a..9b02819 100644
--- a/hitlist.h
+++ b/hitlist.h
@@ -18,6 +18,9 @@
 #include <iostream>
 #include <cstdint>
 
+//#define T_SIMPLE_COLOR
+//#define T_NORM_VISUAL
+#define T_DIFFUSE
 
 // A world, T is color depth
 template<typename T>
@@ -35,40 +38,60 @@ public:
     }
 
     // Given a ray, compute the color.
-    pixel<T> color(const ray3d &r) const {
-        // Detect hits
-        bool hit = false;
-        double hit_t = std::numeric_limits<double>::infinity();
-        std::shared_ptr<object> hit_obj;
-        // Check the nearest object we hit
-        for (const auto &obj: objects) {
-            double t_;
-            if (obj->hit(r, t_, 0.0) && t_ < hit_t) {
-                hit = true;
-                hit_t = t_;
-                hit_obj = obj;
+    pixel<T> color(ray3d r, random_uv_gen_3d &ruvg, uint_fast32_t max_recursion_depth = 64) const {
+        double decay = 1;
+        while (max_recursion_depth-- > 0) {
+            // Detect hits
+            bool hit = false;
+            double hit_t = std::numeric_limits<double>::infinity();
+            std::shared_ptr<object> hit_obj;
+            // Check the nearest object we hit
+            for (const auto &obj: objects) {
+                double t_;
+                if (obj->hit(r, t_, 0.0) && t_ < hit_t) {
+                    hit = true;
+                    hit_t = t_;
+                    hit_obj = obj;
+                }
+            }
+            if (hit) {
+#ifdef T_SIMPLE_COLOR
+                // simply returns color of the object
+                return hit_obj->color();
+#endif
+#ifdef T_NORM_VISUAL
+                // normal vector on hit point
+                const auto nv = hit_obj->normal_vector(r.at(hit_t));
+                // visualize normal vector at hit point
+                return pixel<T>::from_normalized(nv);
+#endif
+#ifdef T_DIFFUSE
+                const auto hit_point = r.at(hit_t); // hit point, on the surface
+                auto nv = hit_obj->normal_vector(hit_point);
+                if (dot(nv, r.direction()) > 0) return pixel<T>::black(); // discard rays from inner (or invert nv)
+                vec3d diffuse_target = hit_point + nv + ruvg();
+                decay *= 0.5; // lose 50% light when diffused
+                r = ray3d{hit_point, diffuse_target - hit_point}; // the new diffused ray we trace on
+                continue;
+#endif
             }
-        }
-        if (hit) {
-            // normal vector on hit point
-            const auto nv = hit_obj->normal_vector(r.at(hit_t));
-//                return obj->color();
-            // visualize normal vector at hit point
-            return pixel<T>::from_normalized(nv);
-        }
-
 
-        // Does not hit anything. Get background color (infinity)
-        const auto u = (r.direction().y + 1.0) * 0.5;
-        return mix(
-                pixel<T>::from_normalized(1.0, 1.0, 1.0),
-                pixel<T>::from_normalized(0.5, 0.7, 1.0),
-                1.0 - u,
-                u
-        );
+            // Does not hit anything. Get background color (infinity)
+            const auto u = (r.direction().y + 1.0) * 0.5;
+            const auto c = mix(
+                    pixel<T>::from_normalized(1.0, 1.0, 1.0),
+                    pixel<T>::from_normalized(0.5, 0.7, 1.0),
+                    1.0 - u,
+                    u
+            );
+#ifdef T_DIFFUSE
+            return decay * c;
+#else
+            return c;
+#endif
+        }
+        return pixel<T>::black(); // reached recursion time limit, very little light
     }
-
-
 };
 
 using hitlist8b = hitlist<uint8_t>;
-- 
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