1 files changed, 163 insertions, 0 deletions
diff --git a/libdimension/model/objects/triangle.c b/libdimension/model/objects/triangle.c
new file mode 100644
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+++ b/libdimension/model/objects/triangle.c
@@ -0,0 +1,163 @@
+/*************************************************************************
+ * Copyright (C) 2009-2014 Tavian Barnes <tavianator@tavianator.com>     *
+ *                                                                       *
+ * This file is part of The Dimension Library.                           *
+ *                                                                       *
+ * The Dimension Library is free software; you can redistribute it and/  *
+ * or modify it under the terms of the GNU Lesser General Public License *
+ * as published by the Free Software Foundation; either version 3 of the *
+ * License, or (at your option) any later version.                       *
+ *                                                                       *
+ * The Dimension Library is distributed in the hope that it will be      *
+ * useful, but WITHOUT ANY WARRANTY; without even the implied warranty   *
+ * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU  *
+ * Lesser General Public License for more details.                       *
+ *                                                                       *
+ * You should have received a copy of the GNU Lesser General Public      *
+ * License along with this program.  If not, see                         *
+ * <http://www.gnu.org/licenses/>.                                       *
+ *************************************************************************/
+
+/**
+ * @file
+ * Triangles.  See
+ * http://tavianator.com/2014/05/a-beautiful-raytriangle-intersection-method/
+ * for a description of the intersection algorithm.
+ */
+
+#include "internal.h"
+#include "dimension/model.h"
+
+/// Optimized ray/triangle intersection test.
+static inline bool
+dmnsn_ray_triangle_intersection(dmnsn_ray l, double *t, double *u, double *v)
+{
+  // See the change of basis in dmnsn_triangle_basis()
+  *t = -l.x0.z/l.n.z;
+  *u = l.x0.x + (*t)*l.n.x;
+  *v = l.x0.y + (*t)*l.n.y;
+  return *t >= 0.0 && *u >= 0.0 && *v >= 0.0 && *u + *v <= 1.0;
+}
+
+/// Triangle intersection callback.
+DMNSN_HOT static bool
+dmnsn_triangle_intersection_fn(const dmnsn_object *object, dmnsn_ray l,
+                               dmnsn_intersection *intersection)
+{
+  double t, u, v;
+  if (dmnsn_ray_triangle_intersection(l, &t, &u, &v)) {
+    intersection->t = t;
+    intersection->normal = dmnsn_z;
+    return true;
+  }
+
+  return false;
+}
+
+/// Triangle inside callback.
+static bool
+dmnsn_triangle_inside_fn(const dmnsn_object *object, dmnsn_vector point)
+{
+  return false;
+}
+
+/// Triangle bounding callback.
+static dmnsn_aabb
+dmnsn_triangle_bounding_fn(const dmnsn_object *object, dmnsn_matrix trans)
+{
+  dmnsn_vector a = dmnsn_transform_point(trans, dmnsn_zero);
+  dmnsn_vector b = dmnsn_transform_point(trans, dmnsn_x);
+  dmnsn_vector c = dmnsn_transform_point(trans, dmnsn_y);
+
+  dmnsn_aabb box = dmnsn_new_aabb(a, a);
+  box = dmnsn_aabb_swallow(box, b);
+  box = dmnsn_aabb_swallow(box, c);
+  return box;
+}
+
+/// Triangle vtable.
+static const dmnsn_object_vtable dmnsn_triangle_vtable = {
+  .intersection_fn = dmnsn_triangle_intersection_fn,
+  .inside_fn = dmnsn_triangle_inside_fn,
+  .bounding_fn = dmnsn_triangle_bounding_fn,
+};
+
+/// Smooth triangle type.
+typedef struct {
+  dmnsn_object object;
+  dmnsn_vector na, nab, nac;
+} dmnsn_smooth_triangle;
+
+/// Smooth triangle intersection callback.
+DMNSN_HOT static bool
+dmnsn_smooth_triangle_intersection_fn(const dmnsn_object *object, dmnsn_ray l,
+                                      dmnsn_intersection *intersection)
+{
+  const dmnsn_smooth_triangle *triangle = (const dmnsn_smooth_triangle *)object;
+
+  double t, u, v;
+  if (dmnsn_ray_triangle_intersection(l, &t, &u, &v)) {
+    intersection->t = t;
+    intersection->normal = dmnsn_vector_add(
+      triangle->na,
+      dmnsn_vector_add(
+        dmnsn_vector_mul(u, triangle->nab),
+        dmnsn_vector_mul(v, triangle->nac)
+      )
+    );
+    return true;
+  }
+
+  return false;
+}
+
+/// Smooth triangle vtable.
+static const dmnsn_object_vtable dmnsn_smooth_triangle_vtable = {
+  .intersection_fn = dmnsn_smooth_triangle_intersection_fn,
+  .inside_fn = dmnsn_triangle_inside_fn,
+  .bounding_fn = dmnsn_triangle_bounding_fn,
+};
+
+/// Make a change-of-basis matrix.
+static inline dmnsn_matrix
+dmnsn_triangle_basis(dmnsn_vector vertices[3])
+{
+  // The new vector space has corners at <1, 0, 0>, <0, 1, 0>, and 0,
+  // corresponding to the basis (ab, ac, ab X ac).
+  dmnsn_vector ab = dmnsn_vector_sub(vertices[1], vertices[0]);
+  dmnsn_vector ac = dmnsn_vector_sub(vertices[2], vertices[0]);
+  dmnsn_vector normal = dmnsn_vector_cross(ab, ac);
+  return dmnsn_new_matrix4(ab, ac, normal, vertices[0]);
+}
+
+dmnsn_object *
+dmnsn_new_triangle(dmnsn_pool *pool, dmnsn_vector vertices[3])
+{
+  dmnsn_object *object = dmnsn_new_object(pool);
+  object->vtable = &dmnsn_triangle_vtable;
+  object->intrinsic_trans = dmnsn_triangle_basis(vertices);
+  return object;
+}
+
+dmnsn_object *
+dmnsn_new_smooth_triangle(dmnsn_pool *pool, dmnsn_vector vertices[3], dmnsn_vector normals[3])
+{
+  dmnsn_matrix P = dmnsn_triangle_basis(vertices);
+
+  // Transform the given normals.
+  dmnsn_vector na = dmnsn_vector_normalized(dmnsn_transform_normal(P, normals[0]));
+  dmnsn_vector nb = dmnsn_vector_normalized(dmnsn_transform_normal(P, normals[1]));
+  dmnsn_vector nc = dmnsn_vector_normalized(dmnsn_transform_normal(P, normals[2]));
+
+  dmnsn_smooth_triangle *triangle = DMNSN_PALLOC(pool, dmnsn_smooth_triangle);
+  triangle->na  = na;
+  triangle->nab = dmnsn_vector_sub(nb, na);
+  triangle->nac = dmnsn_vector_sub(nc, na);
+
+  dmnsn_object *object = &triangle->object;
+  dmnsn_init_object(object);
+  object->vtable = &dmnsn_smooth_triangle_vtable;
+  object->intrinsic_trans = P;
+
+  return object;
+}