Shading with Surface NormalsHEADmaster

1 files changed, 13 insertions, 5 deletions

diff --git a/apps/main.cc b/apps/main.cc
index 4884f6e..2a73d94 100644
--- a/apps/main.cc
+++ b/apps/main.cc
@@ -20,21 +20,29 @@
 
 #include <iostream>
 
-bool hit_sphere(const point3& center, double radius, const ray& r){
+double 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 );
+
+  if ( discriminant < 0 ) {
+    return -1.0;
+  } else {
+    return ( -b - std::sqrt( discriminant ) ) / ( 2.0 * a );
+  }
 }
 
 color ray_color( const ray& r )
 {
-  if ( hit_sphere( point3( 0, 0, -1 ), 0.5, r ) )
-    return color( 1, 0, 0 );
+  auto t = hit_sphere( point3( 0, 0, -1 ), 0.5, r );
+  if ( t > 0.0 ) {
+    vec3 N = unit_vector( r.at( t ) - vec3( 0, 0, -1 ) );
+    return 0.5 * color( N.x() + 1, N.y() + 1, N.z() + 1 );
+  }
 
-    
   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 );