## 2019年6月13日木曜日

### Python - Triangles - Intersecting a Ray with a Triangle - parallel

The Ray Tracer Challenge: A Test-Driven Guide to Your First 3D Renderer (Jamis Buck(著)、Pragmatic Bookshelf)、Chapter 15(Triangles)のTriangles、Test #3 to 7(Intersecting a Ray with a Triangle)、Parallelを取り組んでみる。

コード

triangles_test.py

```#!/usr/bin/env python3
from unittest import TestCase, main
from tuples import Point, Vector
from triangles import Triangle
from rays import Ray

class TriangleTest(TestCase):
def setUp(self):
pass

def tearDown(self):
pass

def test_init(self):
point1 = Point(0, 1, 0)
point2 = Point(-1, 0, 0)
point3 = Point(1, 0, 0)
triangle = Triangle(point1, point2, point3)
self.assertEqual(triangle.point1, point1)
self.assertEqual(triangle.point2, point2)
self.assertEqual(triangle.point3, point3)
self.assertEqual(triangle.edge1, Vector(-1, -1, 0))
self.assertEqual(triangle.edge2, Vector(1, -1, 0))
self.assertEqual(triangle.normal, Vector(0, 0, -1))

def test_finding_normal_vector(self):
triangle = Triangle(Point(0, 1, 0), Point(-1, 0, 0), Point(1, 0, 0))
normal_vector1 = triangle.local_normal_at(Point(0, 0.5, 0))
normal_vector2 = triangle.local_normal_at(Point(-0.5, 0.75, 0))
normal_vector3 = triangle.local_normal_at(Point(0.5, 0.25, 0))
self.assertEqual(normal_vector1, triangle.normal)
self.assertEqual(normal_vector2, triangle.normal)
self.assertEqual(normal_vector3, triangle.normal)

def test_intersecting_ray_parallel(self):
triangle = Triangle(Point(0, 1, 0), Point(-1, 0, 0), Point(1, 0, 0))
ray = Ray(Point(0, -1, -2), Vector(0, 1, 0))
intersections = triangle.intersect(ray)
self.assertEqual(len(intersections), 0)

if __name__ == '__main__':
main()
```

triangles.py

```from tuples import EPSILON
from intersections import Intersections, Intersection

class Triangle:
def __init__(self, point1, point2, point3):
self.point1 = point1
self.point2 = point2
self.point3 = point3
self.edge1 = point2 - point1
self.edge2 = point3 - point1
self.normal = self.edge2.cross(self.edge1).normalize()

def local_normal_at(self, point):
return self.normal

def intersect(self, ray):
dir_cross_edge2 = ray.direction.cross(self.edge2)
det = self.edge1.dot(dir_cross_edge2)
if abs(det) < EPSILON:
return Intersections()
return Intersections(Intersection(1, triangle))
```

```C:\Users\...>py triangles_test.py
...
----------------------------------------------------------------------
Ran 3 tests in 0.000s

OK

C:\Users\...>
```