reworked Scene::traceRayRecurse() to handle backfaces properly for refraction

git-svn-id: svn://anubis/fart/trunk@378 7f9b0f55-74a9-4bce-be96-3c2cd072584d

scenes/for-test.fart

@@ -3,7 +3,7 @@ scene
 {
     camera
     {
-        position <0, 0, 40>
+        position <0, -40, 40>
         look_at <0, 100, 5>
     }
 
@@ -17,6 +17,12 @@ scene
         color <0, 0.8, 1>
     }
 
+    define material glass
+    {
+        transparency 1
+        refraction 1.5
+    }
+
     plane
     {
         position <0, 0, 1>, 0
@@ -34,7 +40,15 @@ scene
             {
                 radius 10
                 translate <$x, $y, 10>
-                material mat
+                if ($x == 0 && $y == 0)
+                {
+                    material glass
+                    translate <0, 0, 20>
+                }
+                else
+                {
+                    material mat
+                }
             }
         }
     }