From 4dde640671a8278ff6c41ef21f03ba351828009c Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@gmail.com>
Date: Sat, 17 Dec 2011 16:43:19 -0500
Subject: Make triangles smooth.

---
 libdimension/dimension/objects.h | 22 ++++++++++++++++++----
 libdimension/tests/render.c      |  2 +-
 libdimension/triangle.c          | 34 ++++++++++++++++++++++++++++++----
 3 files changed, 49 insertions(+), 9 deletions(-)

(limited to 'libdimension')

diff --git a/libdimension/dimension/objects.h b/libdimension/dimension/objects.h
index 001cb3d..9ce9e46 100644
--- a/libdimension/dimension/objects.h
+++ b/libdimension/dimension/objects.h
@@ -26,14 +26,28 @@
 #include <stdbool.h>
 
 /**
- * A triangle.
+ * A triangle, with normals interpolated between the points.
+ * @param[in] a   The first corner of the triangle.
+ * @param[in] b   The second corner of the triangle.
+ * @param[in] c   The third corner of the triangle.
+ * @param[in] na  The normal at \p a.
+ * @param[in] nb  The normal at \p b.
+ * @param[in] nc  The normal at \p c.
+ */
+dmnsn_object *dmnsn_new_triangle(
+  dmnsn_vector a, dmnsn_vector b, dmnsn_vector c,
+  dmnsn_vector na, dmnsn_vector nb, dmnsn_vector nc
+);
+
+/**
+ * A flat triangle, without normal interpolation.
  * @param[in] a  The first corner of the triangle.
  * @param[in] b  The second corner of the triangle.
  * @param[in] c  The third corner of the triangle.
  */
-dmnsn_object *dmnsn_new_triangle(dmnsn_vector a,
-                                 dmnsn_vector b,
-                                 dmnsn_vector c);
+dmnsn_object *dmnsn_new_flat_triangle(
+  dmnsn_vector a, dmnsn_vector b, dmnsn_vector c
+);
 
 /**
  * A plane.
diff --git a/libdimension/tests/render.c b/libdimension/tests/render.c
index 41b19b4..58a7930 100644
--- a/libdimension/tests/render.c
+++ b/libdimension/tests/render.c
@@ -240,7 +240,7 @@ dmnsn_test_scene_add_triangle_strip(dmnsn_scene *scene)
   strip_textures[2]->pigment =
     dmnsn_new_solid_pigment(DMNSN_TCOLOR(dmnsn_yellow));
   for (unsigned int i = 0; i < 128; ++i) {
-    dmnsn_object *triangle = dmnsn_new_triangle(a, b, c);
+    dmnsn_object *triangle = dmnsn_new_flat_triangle(a, b, c);
     triangle->texture = strip_textures[i%3];
     DMNSN_INCREF(triangle->texture);
     dmnsn_array_push(strip_array, &triangle);
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);
+}
-- 
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