1 files changed, 30 insertions, 4 deletions

diff --git a/libdimension/triangle.c b/libdimension/triangle.c
index f224aa9..a176414 100644
--- a/libdimension/triangle.c
+++ b/libdimension/triangle.c
@@ -26,7 +26,7 @@
 #include "dimension.h"
 
 typedef struct dmnsn_triangle_payload {
-  dmnsn_vector a, ab, ac, normal;
+  dmnsn_vector a, ab, ac, na, nab, nac, normal;
 } dmnsn_triangle_payload;
 
 /** Triangle intersection callback. */
@@ -43,7 +43,13 @@ dmnsn_triangle_intersection_fn(const dmnsn_object *triangle, dmnsn_line l,
   double v = -dmnsn_vector_dot(l.n, dmnsn_vector_cross(payload->ab, ax0))/den;
   if (t >= 0.0 && u >= 0.0 && v >= 0.0 && u + v <= 1.0) {
     intersection->t      = t;
-    intersection->normal = payload->normal;
+    intersection->normal = dmnsn_vector_add(
+      payload->na,
+      dmnsn_vector_add(
+        dmnsn_vector_mul(u, payload->nab),
+        dmnsn_vector_mul(v, payload->nac)
+      )
+    );
     return true;
   }
 
@@ -59,17 +65,24 @@ dmnsn_triangle_inside_fn(const dmnsn_object *triangle, dmnsn_vector point)
 
 /* Allocate a new triangle */
 dmnsn_object *
-dmnsn_new_triangle(dmnsn_vector a, dmnsn_vector b, dmnsn_vector c)
+dmnsn_new_triangle(dmnsn_vector a, dmnsn_vector b, dmnsn_vector c,
+                   dmnsn_vector na, dmnsn_vector nb, dmnsn_vector nc)
 {
-  dmnsn_object *triangle = dmnsn_new_object();
+  na = dmnsn_vector_normalized(na);
+  nb = dmnsn_vector_normalized(nb);
+  nc = dmnsn_vector_normalized(nc);
 
   dmnsn_triangle_payload *payload =
     dmnsn_malloc(sizeof(dmnsn_triangle_payload));
   payload->a      = a;
+  payload->na     = na;
   payload->ab     = dmnsn_vector_sub(b, a);
+  payload->nab    = dmnsn_vector_sub(nb, na);
   payload->ac     = dmnsn_vector_sub(c, a);
+  payload->nac    = dmnsn_vector_sub(nc, na);
   payload->normal = dmnsn_vector_cross(payload->ab, payload->ac);
 
+  dmnsn_object *triangle     = dmnsn_new_object();
   triangle->ptr              = payload;
   triangle->intersection_fn  = dmnsn_triangle_intersection_fn;
   triangle->inside_fn        = dmnsn_triangle_inside_fn;
@@ -78,3 +91,16 @@ dmnsn_new_triangle(dmnsn_vector a, dmnsn_vector b, dmnsn_vector c)
   triangle->bounding_box.max = dmnsn_vector_max(dmnsn_vector_max(a, b), c);
   return triangle;
 }
+
+/* Allocate a new flat triangle */
+dmnsn_object *
+dmnsn_new_flat_triangle(dmnsn_vector a, dmnsn_vector b, dmnsn_vector c)
+{
+  /* Flat triangles are just smooth triangles with identical normals at all
+     verticies */
+  dmnsn_vector normal = dmnsn_vector_cross(
+    dmnsn_vector_sub(b, a),
+    dmnsn_vector_sub(c, a)
+  );
+  return dmnsn_new_triangle(a, b, c, normal, normal, normal);
+}