Add HW3 triangle implementation

Homework3/solution.go

@@ -0,0 +1,93 @@
+package main
+
+import (
+	"github.com/fmi/go-homework/geom"
+)
+
+const Episilon = 1e-7
+
+type Triangle struct {
+	a, b, c geom.Vector
+}
+
+type Quad struct {
+	a, b, c, d geom.Vector
+}
+
+type Sphere struct {
+	origin geom.Vector
+	r      float64
+}
+
+func NewTriangle(a, b, c geom.Vector) Triangle {
+	return Triangle{
+		a: a,
+		b: b,
+		c: c,
+	}
+}
+
+func NewQuad(a, b, c, d geom.Vector) Quad {
+	return Quad{
+		a: a,
+		b: b,
+		c: c,
+		d: d,
+	}
+}
+
+func NewSphere(origin geom.Vector, r float64) Sphere {
+	return Sphere{
+		origin: origin,
+		r:      r,
+	}
+}
+
+func (triangle Triangle) Intersect(ray geom.Ray) bool {
+	// Find vectors for two edges sharing vertex 0
+	edge1 := geom.Sub(triangle.b, triangle.a)
+	edge2 := geom.Sub(triangle.c, triangle.a)
+
+	// Begin calculating determinant
+	h := geom.Cross(ray.Direction, edge2)
+
+	det := geom.Dot(edge1, h)
+	if det > -Episilon && det < Episilon {
+		return false // The ray is parallel to triangle plane, impossible that they intersect
+	}
+
+	f := 1 / det
+
+	// Calculate vector from vertex to the ray origin
+	s := geom.Sub(ray.Origin, triangle.a)
+
+	// Calculating U parameter
+	u := f * geom.Dot(s, h)
+	if u < 0 || u > 1 {
+		return false
+	}
+
+	// Prepare to test V parameter
+	q := geom.Cross(s, edge1)
+
+	v := f * geom.Dot(ray.Direction, q)
+	if v < 0 || u+v > 1 {
+		return false
+	}
+
+	// Calculating t - final check to see if ray intersects triangle
+	t := f * geom.Dot(edge2, q)
+	if t > Episilon {
+		return true
+	}
+
+	return false
+}
+
+func (quad Quad) Intersect(ray geom.Ray) bool {
+	return true
+}
+
+func (sphere Sphere) Intersect(ray geom.Ray) bool {
+	return true
+}

Homework3/solution_test.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/fmi/go-homework/geom"
+)
+
+func TestSampleSimpleOperations(t *testing.T) {
+	var prim geom.Intersectable
+
+	a, b, c := geom.NewVector(-1, -1, 0), geom.NewVector(1, -1, 0), geom.NewVector(0, 1, 0)
+	prim = NewTriangle(a, b, c)
+	ray := geom.NewRay(geom.NewVector(0, 0, -1), geom.NewVector(0, 0, 1))
+
+	if !prim.Intersect(ray) {
+		t.Errorf("Expected ray %#v to intersect triangle %#v but it did not.", ray, prim)
+	}
+}
+
+func TestSampleIntersectableImplementations(t *testing.T) {
+	var prim geom.Intersectable
+
+	a, b, c, d := geom.NewVector(-1, -1, 0),
+		geom.NewVector(1, -1, 0),
+		geom.NewVector(0, 1, 0),
+		geom.NewVector(-1, 1, 0)
+
+	prim = NewTriangle(a, b, c)
+	prim = NewQuad(a, b, c, d)
+	prim = NewSphere(a, 5)
+
+	_ = prim
+}