From 92329f633db517252c86e54219484ec4c964815b Mon Sep 17 00:00:00 2001
From: K Tyl <me@ktyl.dev>
Date: Sat, 6 Jun 2020 23:01:46 +0100
Subject: [PATCH] diffuse materials

---
 src/colour.h |  8 ++++----
 src/main.cpp | 17 ++++++++++++-----
 src/vec3.h   | 22 ++++++++++++++++++++++
 3 files changed, 38 insertions(+), 9 deletions(-)

diff --git a/src/colour.h b/src/colour.h
index 95d02d5..1347b08 100755
--- a/src/colour.h
+++ b/src/colour.h
@@ -10,11 +10,11 @@ void write_colour(std::ostream &out, colour pixel_colour, int samples_per_pixel)
     auto g = pixel_colour.y();
     auto b = pixel_colour.z();
 
-    // divide the colour total by the number of samples
+    // divide the colour total by the number of samples and gamme-correct for gamma=2.0
     auto scale = 1.0 / samples_per_pixel;
-    r *= scale;
-    g *= scale;
-    b *= scale;
+    r = sqrt(scale * r);
+    g = sqrt(scale * g);
+    b = sqrt(scale * b);
     
     // write the translated [0,255] value of each colour component.
     out << static_cast<int>(256 * clamp(r, 0.0, 0.999)) << ' '
diff --git a/src/main.cpp b/src/main.cpp
index e34542a..f07d189 100755
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -11,20 +11,27 @@ const double ASPECT_RATIO = 16.0 / 9.0;
 const int WIDTH = 384;
 const int HEIGHT = static_cast<int>(WIDTH / ASPECT_RATIO);
 const int SAMPLES_PER_PIXEL = 100;
+const int MAX_DEPTH = 50;
 
-colour ray_colour(const ray& r, const hittable& world)
+colour ray_colour(const ray& r, const hittable& world, int depth)
 {
     hit_record rec;
+    if (depth <= 0)
+    {
+        return colour(0,0,0);
+    }
+
     if (world.hit(r, 0, infinity, rec))
     {
-        return 0.5 * (rec.normal + colour(1,1,1));
+        point3 target = rec.p + rec.normal + random_in_unit_sphere();
+        return 0.5 * ray_colour(ray(rec.p, target - rec.p), world, depth-1);
     }
 
     vec3 unit_direction = unit_vector(r.direction());
     auto t = 0.5 * (unit_direction.y() + 1.0);
 
-    auto a = colour(1.0, 0.5, 0.6);
-    auto b = colour(0.0, 0.0, 0.0);
+    auto a = colour(0.5, 0.6, 0.7);
+    auto b = colour(1.0, 1.0, 1.0);
 
     return lerp(a, b, t);
 }
@@ -60,7 +67,7 @@ int main()
                 auto u = (i + random_double()) / (WIDTH-1);
                 auto v = (j + random_double()) / (HEIGHT-1);
                 ray r = cam.get_ray(u, v);
-                pixel_colour += ray_colour(r, world);
+                pixel_colour += ray_colour(r, world, MAX_DEPTH);
             }
 
             write_colour(std::cout, pixel_colour, SAMPLES_PER_PIXEL);
diff --git a/src/vec3.h b/src/vec3.h
index c0084a7..f562294 100755
--- a/src/vec3.h
+++ b/src/vec3.h
@@ -3,9 +3,21 @@
 #include <cmath>
 #include <iostream>
 
+#include "rtweekend.h"
+
 class vec3
 {
 public:
+    inline static vec3 random()
+    {
+        return vec3(random_double(),random_double(),random_double());
+    }
+
+    inline static vec3 random(double min, double max)
+    {
+        return vec3(random_double(min,max),random_double(min,max),random_double(min,max));
+    }
+
     vec3() : e{0,0,0} {}
     vec3(double e0, double e1, double e2) : e{e0, e1, e2} {}
 
@@ -116,3 +128,13 @@ inline vec3 unit_vector(vec3 v)
 {
     return v / v.length();
 }
+
+vec3 random_in_unit_sphere()
+{
+    while (true)
+    {
+        auto p = vec3::random(-1,1);
+        if (p.length_squared() >= 1) continue;
+        return p;
+    }
+}