Adding a Sphere

1 files changed, 13 insertions, 0 deletions

diff --git a/raytracing/apps/main.cc b/raytracing/apps/main.cc
index d5702cd..4884f6e 100644
--- a/raytracing/apps/main.cc
+++ b/raytracing/apps/main.cc
@@ -20,8 +20,21 @@
 
 #include <iostream>
 
+bool hit_sphere(const point3& center, double radius, const ray& r){
+  vec3 oc = center - r.origin();
+  auto a = dot( r.direction(), r.direction() );
+  auto b = -2.0 * dot( r.direction(), oc );
+  auto c = dot( oc, oc ) - radius * radius;
+  auto discriminant = b * b - 4 * a * c;
+  return ( discriminant >= 0 );
+}
+
 color ray_color( const ray& r )
 {
+  if ( hit_sphere( point3( 0, 0, -1 ), 0.5, r ) )
+    return color( 1, 0, 0 );
+
+    
   vec3 unit_direction = unit_vector( r.direction() );
   auto a = 0.5 * ( unit_direction.y() + 1.0 );
   return ( 1.0 - a ) * color( 1.0, 1.0, 1.0 ) + a * color( 0.5, 0.7, 1.0 );