From 1d5d0439283916f190218a827a7cd7f1fe6de600 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop+git@gmail.com>
Date: Tue, 12 Oct 2010 16:39:29 +0000
Subject: [PATCH] reworked Scene::traceRayRecurse() to handle backfaces
 properly for refraction

git-svn-id: svn://anubis/fart/trunk@378 7f9b0f55-74a9-4bce-be96-3c2cd072584d
---
 main/Scene.cc        | 106 ++++++++++++++++++++++++-------------------
 scenes/for-test.fart |  18 +++++++-
 2 files changed, 76 insertions(+), 48 deletions(-)

diff --git a/main/Scene.cc b/main/Scene.cc
index 542ccfa..306ae55 100644
--- a/main/Scene.cc
+++ b/main/Scene.cc
@@ -119,8 +119,7 @@ void Scene::renderPixel(int x, int y, unsigned char * pixel)
 
 Color Scene::traceRay(const Ray & ray)
 {
-    static refptr<Material> air = new Material();
-    return traceRayRecurse(ray, m_max_depth, 1.0, air);
+    return traceRayRecurse(ray, m_max_depth, 1.0, NULL);
 }
 
 /**
@@ -129,7 +128,11 @@ Color Scene::traceRay(const Ray & ray)
 Color Scene::traceRayRecurse(const Ray & ray, int depth, double factor,
         refptr<Material> last_material)
 {
-    Color color;
+    static refptr<Material> air = new Material();
+    Color color(0, 0, 0);
+
+    if (last_material.isNull())
+        last_material = air;
 
     Shape::Intersection hit = getRayClosestHit(ray);
 
@@ -139,52 +142,63 @@ Color Scene::traceRayRecurse(const Ray & ray, int depth, double factor,
         refptr<Material> material = hit.shape->getMaterial();
 
         /* check for backfaces */
-        if (ray.getDirection() % hit.normal > 0.0)
+        bool frontface = ray.getDirection() % hit.normal < 0.0;
+
+        if (frontface)
         {
-            /* if dot product is positive, this is a back-face */
-            hit.normal = -hit.normal;
+            color = computePhong(material,
+                                 ray,
+                                 hit.position,
+                                 hit.normal);
+
+            if (depth > 0 && factor > SCENE_FACTOR_THRESHOLD)
+            {
+                double reflectance = material->getReflectance();
+                if (factor * reflectance > SCENE_FACTOR_THRESHOLD)
+                {
+                    color *= (1.0 - reflectance);
+                    Vector reflected_direction =
+                        ray.getDirection().reflect(hit.normal);
+                    Ray newRay(hit.position, reflected_direction);
+                    Vector jitter_surface_point = newRay[0.0001];
+                    Ray jitterNewRay(jitter_surface_point, reflected_direction);
+                    Color c = traceRayRecurse(jitterNewRay,
+                                              depth - 1,
+                                              factor * reflectance,
+                                              material);
+                    color += c * reflectance;
+                }
+
+                double transparency = material->getTransparency();
+                if (factor * transparency > SCENE_FACTOR_THRESHOLD)
+                {
+                    color *= (1.0 - transparency);
+                    Vector jitter_surface_point = hit.position
+                                                  + ray.getDirection() * 0.0001;
+                    Vector refracted_direction =
+                        ray.getDirection().refract(hit.normal,
+                                last_material->getRefraction(),
+                                material->getRefraction());
+                    Ray newRay(jitter_surface_point, refracted_direction);
+                    Color c = traceRayRecurse(newRay,
+                                              depth - 1,
+                                              factor * transparency,
+                                              material);
+                    color += c * transparency;
+                }
+            }
         }
-
-        color = computePhong(material,
-                             ray,
-                             hit.position,
-                             hit.normal);
-
-        if (depth > 0 && factor > SCENE_FACTOR_THRESHOLD)
+        else
         {
-            double reflectance = material->getReflectance();
-            if (factor * reflectance > SCENE_FACTOR_THRESHOLD)
-            {
-                color *= (1.0 - reflectance);
-                Vector reflected_direction =
-                    ray.getDirection().reflect(hit.normal);
-                Ray newRay(hit.position, reflected_direction);
-                Vector jitter_surface_point = newRay[0.0001];
-                Ray jitterNewRay(jitter_surface_point, reflected_direction);
-                Color c = traceRayRecurse(jitterNewRay,
-                                          depth - 1,
-                                          factor * reflectance,
-                                          material);
-                color += c * reflectance;
-            }
-
-            double transparency = material->getTransparency();
-            if (factor * transparency > SCENE_FACTOR_THRESHOLD)
-            {
-                color *= (1.0 - transparency);
-                Vector jitter_surface_point = hit.position
-                                              + ray.getDirection() * 0.0001;
-                Vector refracted_direction =
-                    ray.getDirection().refract(hit.normal,
-                            last_material->getRefraction(),
-                            material->getRefraction());
-                Ray newRay(jitter_surface_point, refracted_direction);
-                Color c = traceRayRecurse(newRay,
-                                          depth - 1,
-                                          factor * transparency,
-                                          material);
-                color += c * transparency;
-            }
+            material = air;
+            Vector jitter_surface_point = hit.position
+                                          + ray.getDirection() * 0.0001;
+            Vector refracted_direction =
+                ray.getDirection().refract(-hit.normal,
+                        last_material->getRefraction(),
+                        material->getRefraction());
+            Ray newRay(jitter_surface_point, refracted_direction);
+            color = traceRayRecurse(newRay, depth, factor, material);
         }
     }
 
diff --git a/scenes/for-test.fart b/scenes/for-test.fart
index fdef550..1288cd5 100644
--- a/scenes/for-test.fart
+++ b/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
+                }
             }
         }
     }